New methods for assessing secondary performance attributes of sunscreens suitable for professional outdoor work

BACKGROUND

Outdoor workers (OW) are highly exposed to solar ultraviolet radiation (UVR) and thus at increased risk for developing skin cancer. An essential part of an overall strategy to reduce workplace UVR-exposure to OW's skin is the usage of sunscreens. However, compliance with regular sunscreen usage seems to be low, as products are usually designed for recreational sun exposure and thus do not meet the requirements of physically active OW. To date, no standardized test procedures assess the suitability of sunscreens for professional use. The aim of this pilot study was to develop standardized methods of testing secondary performance attributes (PA) to represent real-life working conditions of outdoor work.

METHODS

Ten sunscreen products, carefully selected after a detailed market survey of all relevant producers available on the German market, were evaluated regarding their suitability for professional outdoor work on 24 healthy volunteers in a newly designed test procedure. In addition to three standardized efficacy characteristics, i.e., sun protection factor, water-resistance, and UVA protection, we evaluated each PA involving parameters typically associated with outdoor workplaces.

RESULTS

We developed standardized methods for objectifying the suitability of sunscreen products for professional outdoor work. The test procedures used are well feasible and appropriate for testing the PA because they represent practical working conditions in detail - although the degree of discriminability of single test methods varied. The claimed sun protection factor (SPF) of the products was confirmed; bio-stability of the SPF after physical activity was achieved in most cases. While most products hardly irritate the eyes and are quickly absorbed, the evaluation of the subjective skin feeling and non-slip grip is inconsistent.

CONCLUSIONS

In this pilot study, for the first time secondary PA are defined and examined. Although further objectification of the PA assessment as well as the establishment of minimum standards should be sought, the new methods could already complement the so far mandatory labels and in this way provide a significant impetus for the current scientific and political focus on the improvement of occupational health in highly UVR-exposed OW.

Preliminary testing for normality: some statistical aspects of a common concept

BACKGROUND

Statistical methodology has become an increasingly important topic in dermatological research. Adequacy of the statistical procedure depends among others on distributional assumptions. In dermatological articles, the choice between parametric and nonparametric methods is often based on preliminary goodness-of-fit tests.

AIM

For the special case of the assumption of normally distributed data, the Kolmogorov-Smirnov test is the most popular choice. We investigated the performance of this test on four types of non-normal data, representing the majority of real data in dermatological research.

METHODS

Simulations were run to assess the performance of the Kolmogorov-Smirnov test, depending on sample size and severity of violations of normality.

RESULTS

The Kolmogorov-Smirnov test performs badly on data with single outliers, 10% outliers and skewed data at sample sizes < 100, whereas normality is rejected to an acceptable degree for Likert-type data.

CONCLUSION

Preliminary testing for normality is not recommended for small-to-moderate sample sizes.

Meso- and Microscale Patterns of Fusarium Head Blight in Spring Wheat Fields in Minnesota

Several techniques were used to study the spatial distribution of Fusarium head blight (FHB) in spring wheat fields in the Red River Valley of Minnesota in 2001 and 2002. Four scales of study were analyzed, ranging from countywide comparisons down to adjacent heads. Agreement to frequency distributions and the departure from randomness, along with the autocorrelation of FHB clusters, were calculated at each scale. Regression analysis also was used to describe any edge affects that might exist. Finally, the optimal number of samples to adequately assess a 32.4-ha (80-acre) field was determined to a precision of ±5% disease incidence (DI). The analysis showed that DI had a random pattern at scales smaller than 32.4-ha fields, including quadrats of 6,561, 729, and 9 m², as well 0.8-m transects involving consecutive heads within drill rows. There was no difference in DI associated with edges of fields compared with the incidence of FHB in transects within fields. Analysis of the spatial distribution at the mesoscale (county and township) showed no association in FHB DI between fields based on proximity. Differences were attributed to previous crop and in-field residue. Disease incidence was most accurately assessed on a field-by-field basis. The optimal sampling size (with <5% error) for surveying for the incidence of FHB in a standard commercial field was seven 20-head samples. Regional disease estimates would improve from including more fields at the expense of fewer samples per field.

Quantitative assessment of primary skin irritants in vitro in a cytotoxicity model: comparison with in vivo human irritation tests

BACKGROUND

While great efforts have been made in recent years to develop in vitro methods for assessing skin irritation potential, there are relatively few data that correlate in vitro data with in vivo data.

OBJECTIVES

To expand our previously reported investigations on in vitro vs. in vivo correlation of a series of homologous N-alkyl sulphates of different alkyl chain length to include primary skin irritants of different chemical classes.

METHODS

Anionic surfactants (three different sodium alkyl sulphonates and sodium lauryl sulphate), cationic surfactants (three alkyl trimethyl ammonium bromides), non-ionic surfactants (polyoxyethylene-20-cetyl ether and Tween 20), benzoic acid, dimethyl sulphoxide and phenol were chosen as model irritants. A spontaneously immortalized human keratinocyte line, HaCaT, was used as an in vitro model to predict the cutaneous irritation. The end-point used to assess toxicity was uptake of the vital dye neutral red (NR) 24 h after dosing. The cytotoxicity data from these assays were compared with the irritant responses (as evaluated by measurement of erythema and transepidermal water loss) obtained after 24-h application of the same compounds (100 microL of 20 mmol L(-1) aqueous solution) to the volar forearm of human volunteers.

RESULTS

All tested irritants had cytotoxic effects as demonstrated by a decreased NR uptake, which showed a clear dose-response relationship. Concentrations resulting in 50% inhibition of NR uptake (IC(50)) ranged from 8 micromol L(-1) (hexadecyl trimethyl ammonium bromide) to 328 mmol L(-1) (dimethyl sulphoxide). We found a good overall correlation between in vitro cytotoxicity (NR uptake IC(50) values) and in vivo irritation potential in humans. Only the high molecular weight compounds Tween 20 and polyoxyethylene-20-cethyl ether were problematic, as their irritation potential was overestimated by the in vitro assay. This non-conformity of these high molecular weight (> 1000) compounds was expected, and can be largely attributed to the epidermal permeability barrier. The epidermal barrier, which greatly limits the percutaneous penetration of xenobiotics in vivo, does not exist in cell culture models.

CONCLUSIONS

The in vitro cytotoxicity model is a useful screening tool, but data should be interpreted critically and require confirmation by appropriate in vivo studies.

Scale-sensitive fractal analysis using the patchwork method for the assessment of skin roughness

BACKGROUND/AIMS

As skin roughness and wrinkles are easily perceived by the consumer, quantifying skin surface structures is a vital parameter for cosmetic product development. As more tools are available for measuring three-dimensional (3-D) surface data, instead of two-dimensional (2-D) profile lines, new algorithms are desirable, to take advantage of the information gathered.

METHODS

The patchwork method tiles topographic data sets virtually and analyzes the change in apparent area as a function of tile scale. The patchwork method and conventional 2-D profilometric analysis were applied to 24 topographic skin data sets. The data sets were derived before and after application of 15% glycerol solution on the skin of eight volunteers.

RESULTS

One hour after application, skin roughness decreased by 20.8%, as measured by conventional analysis, and by 23.3%, as measured by the patchwork method. For both methods, the differences were not significant.

CONCLUSIONS

The patchwork method can be applied to skin data and renders results similar in intensity and direction to conventional 2-D analysis. It is advantageous over conventional 2-D analysis in three ways: it makes use of the full topologic information, it requires no high-pass or low-pass filtering, and it is independent of the anisotropy of the skin.

Role of flavonoids in controlling the phototoxicity of Hypericum perforatum extracts

Hypericum perforatum extracts are used mainly as oral antidepressants. Depending on source the extracts contain various amounts of phenylpropanes, flavonol derivates, biflavones, proathocyanidines, xanthones, phloroglucinoles, some amino acids, naphtodianthrones (hypericines) and essential oil constituents. The therapeutic use of Hypericum perforatum extracts however is limited by their phototoxic potential. It was the aim of the present study to investigate the phototoxic potential of 3 Hypericum perforatum extracts from different sources as well as some of its main constituents. In order to systematically study the phototoxic potential we established a modified neutral red assay utilizing an immortalized human keratinocyte cell line (HaCaT cells) as substrate and UVA irradiation. This modified neutral red assay was found to be a simple and reliable method for detecting phototoxic effects of reference agents and plant extracts. The validity of this method was demonstrated with known phototoxic compounds like chloropromazine and psoralenes like 5-MOP. Hypericum perforatum extracts demonstrated cytotoxicity and photocytotoxicity in a dose and UVA-dose dependent manner. Hypericine itself also evoked severe phototoxic effects and was thus identified as the main phototoxic constituent. Among the tested flavonoids quercitrin was found to be cytotoxic, while rutin unexpectedly demonstrated phototoxicity whereas quercitrin was effective to control the phototoxic activity of Hypericum perforatum extracts.

Comparison of three techniques for evaluating skin erythemal response for determination of sun protection factors of sunscreens: high resolution laser Doppler imaging, colorimetry and visual scoring

BACKGROUND/PURPOSE

Sun protection factor (SPF) measurement is based on the determination of the minimal erythema dose (MED). The ratio of doses required to induce a minimal erythema between product-treated and untreated skin is defined as SPF. The aim of this study was to validate the conventionally used visual scoring with two non-invasive methods: high resolution laser Doppler imaging (HR-LDI) and colorimetry. Another goal was to check whether suberythemal reactions could be detected by means of HR-LDI measurements.

MATERIALS AND METHODS

Four sunscreens were selected. The measurements were made on the back of 10 subjects. A solar simulator SU 5000 (m.u.t., Wedel, Germany) served as radiation source. For the visual assessment, the erythema was defined according to COLIPA as the first perceptible, clearly defined unambiguous redness of the skin. For the colorimetric determination of the erythema, a Chromameter CR 300 (Minolta, Osaka, Japan) was used. The threshold for the colorimetry was chosen according to the COLIPA recommendation as an increase of the redness parameter delta a* = 2.5. For the non-contact perfusion measurements of skin blood flow, a two-dimensional high resolution laser Doppler imager (HR-LDI) (Lisca, Linköping, Sweden) was used. For the HR-LDI measurements, an optimal threshold perfusion needed to be established.

RESULTS

For the HR-LDI measurements basal perfusion +1 standard deviation of all basal measurements was found to be a reliable threshold perfusion corresponding to the minimal erythema. Smaller thresholds, which would be necessary for detection of suberythemal responses, did not provide unambiguous data. All three methods, visual scoring, colorimetry and HR-LDI, produced similar SPFs for the test products with a variability of < 5% between methods. The HR-LDI method showed the lowest variation of the mean SPF. Neither of the instrumental methods, however, resulted in an increase of the sensitivity of SPF determination as compared with visual scoring.

CONCLUSION

Both HR-LDI and colorimetry are suitable, reliable and observer-independent methods for MED determination. However, they do not provide greater sensitivity and thus do not result in lower UV dose requirements for testing.

SLS-irritated human skin shows no correlation between degree of proliferation and TEWL increase

It is well known that cutaneous irritants influence epidermal proliferation but the pathogenesis is poorly understood. Recent investigations have shown that the skin barrier integrity influences the proliferation of the basal keratinocytes. Our question was whether the proliferating activity of keratinocytes is indeed regulated by the degree of skin barrier damage or by a direct toxic action of the irritant on the keratinocytes. Therefore various degrees of skin irritation were induced by the application of 0.1%, 0.5% and 2% sodium lauryl sulphate (SLS) solution to the forearm skin of six healthy volunteers. This experiment was performed to evaluate the relationship between SLS concentration and epidermal proliferation. In a second experiment another 14 volunteers were treated with a single SLS concentration (0.5%) to look for interindividual differences in the patterns of skin reaction and susceptibility to the irritant. Skin barrier function was evaluated by measurements of transepidermal water loss (TEWL) before and after irritation. Punch biopsies were taken after 96 h from exposed areas and from unexposed normal skin. Dividing keratinocytes were identified immunocytochemically using three different monoclonal antibodies: PCNA, MIB 1 and KiS1. Exposure to SLS resulted in concentration-dependent increases in both TEWL and epidermal proliferation. However, no significant correlation could be found between the degree of hyperproliferation and the TEWL changes. The results suggest that epidermal proliferation is modulated by a direct interaction of the surfactant with the keratinocytes and/or by release of mediators rather than the consequence of a barrier disturbance.

Water diffusion characteristics of human stratum corneum at different anatomical sites in vivo

Despite its heterogeneity, stratum corneum (SC) has been described as a homogeneous membrane for water diffusion. We measured water flux across the SC, transepidermal water loss (TEWL), in six women, in vivo. At four anatomical sites--back, abdomen, forearm, and thigh--we took measurements during sequential tape stripping. The inverse of TEWL (1/TEWL) and removed SC thickness yielded a highly linear correlation (Pearson's r ranging between 0.88 and 0.99). Applying Fick's law of diffusion, we calculated SC thickness (H), and SC water diffusion coefficient (D). Comparing the results, SC of all women was significantly thicker (p < 0.05) at the extremities (12.7 +/- 4.2 microm, mean +/- SD, n = 12) than the abdomen (7.7 +/- 1.8 microm, n = 6). The calculated diffusion coefficient approximated 2.16 +/- 1.14x10(-9) cm2/s. Compared with the diffusion constant found for SC depleted of lipids, our value was 100-fold lower. In agreement with previous findings that intercellular lipids are a rate determining component of the SC barrier, we suggest that water diffuses mainly through the intercellular space. The calculation of H and/or D, however, is based on several variables: SC density, the water concentration difference, and the partition coefficient of water between viable epidermis and SC. The literature values vary widely. It is desirable to determine these parameters more precisely, especially if discrete differences, such as between anatomical sites, are to be revealed.

Cumulative irritation in older and younger skin: a comparison

Changes in stratum corneum properties due to sodium lauryl sulfate cumulative irritation were determined as a function of age. We irritated the backs of 7 younger (27.7 +/- 4.6 years, mean +/- standard deviation) and 10 older (69.8 +/- 5.5 years) volunteers on 5 consecutive days with open application of a 7.5% aqueous sodium lauryl sulfate solution. Water- and untreated skin served as controls. Transepidermal water loss, stratum corneum capacitance, Desquamation Index, and skin roughness parameters were evaluated on 5 days of the 1st week, and on 3 days of the 2nd week. All parameters revealed a delayed and decreased reaction of older compared to younger skin and recovery appeared to be prolonged. We conclude that under these test conditions irritancy to repetitive sodium lauryl sulfate exposure of older versus younger skin resembled that previously observed after single occlusive exposure. In neither age group was the recovery effect reduced by repeated irritation, demonstrating sufficient skin barrier and recovery function.

Interlaboratory evaluation of a human patch test for the identification of skin irritation potential/hazard

The human 4 hr patch test provides an opportunity to identify substances with significant skin irritation potential without recourse to the use of animals. To demonstrate the validity of the method it must be relevant and reliable. It is self-evident that the method is relevant to the identification of skin irritation hazards to humans. However, it is essential that the results be reproducible. This paper presents data on a number of substances tested by different laboratories. Eight substances were tested by two or more laboratories and the data compared with a standard positive control, 20% sodium dodecyl sulfate. In almost all cases, the outcome of this comparison was identical. Thus, despite the fact that there is known variability among human subjects in terms of skin reactivity to irritants, this simple method showed good reproducibility for the classification of acute skin irritation potential. Therefore, it is argued that this human 4-hr patch test is a valid alternative to the equivalent rabbit test for the assessment of skin irritation hazard to humans.

Studies on non-immune immediate contact reactions in an unselected population

Non-immune immediate contact reactions (NIICR) arising from skin contact with a wide range of chemicals have been well described. There is evidence that many, if not all, individuals are susceptible to this effect; it may be just a matter of applying a higher dose to the most resistant types of skin. In this work, we chose to evaluate susceptibility to development of NIICR in a large unselected population. Skin tests were made with 3 known urticants (benzoic acid, trans-cinnamic acid and methyl nicotinate), each at 2 concentrations. In a group of 200 volunteers, it was demonstrated that all 3 chemicals induced NIICR in the majority of people. Approximately 10% of the volunteers appeared particularly sensitive, reacting fairly strongly to 2/3 urticants. In contrast, another subset, also about 10%, failed to respond significantly to any of the chemicals at any dose. However, strong reactivity to one urticant was not predictive of the reaction to the other urticants. In a number of cases, individuals reacting strongly to one urticant reacted very little if at all to the other urticants. Also, the type of response, erythema or oedema, was specific to an individual. There was no significant correlation with age or sex on the degree of NIICR. In conclusion, it has been demonstrated that there is a wide interindividual variation in the response to chemical urticants, which cannot be predicted on the basis of age or sex. The prospect of identifying a panel of individuals generally sensitive to non-immune immediate contact reactions seems limited.

Individual, ethnic and seasonal variability in irritant susceptibility of skin: the implications for a predictive human patch test

Since irritants are the major cause of contact dermatitis, it is important to identify those chemicals that possess significant ability to cause skin irritation. This process must then be followed by risk assessment and risk management. Historically, animal tests have played a major rôle in this process, but human volunteer studies are of increasing importance in this field. Where the appropriate safety and ethical controls are in place, human testing can give data that identifies skin irritation hazard. To be of widest value, these human studies must not be flawed due to inter-individual, inter-ethnic or seasonal variation. We conducted a large dose-response study and studied the impact of summer and winter weather on a predictive human assay. Sodium dodecyl sulphate (SDS) was tested at 0.1%-20% in 3 national groups of approximately 100 volunteers, using 25 mm Hill Top chambers loaded with 0.2 ml, solution and applied to the upper outer arm for 4 h. Reactions were scored at 24, 48 and/or 72 h after patch application. The German and Chinese studies were completed in a few weeks under similar winter conditions, whereas the UK work was spread fairly evenly over about a 15-month period. Some relatively minor differences were observed in the dose-response curves obtained, probably due to weather conditions. The effect of the weather on the intensity, but not the pattern, of irritant reactivity was also evident in the smaller specific study that assessed reactions to SDS in summer and in winter. Whereas 45% of the panel reacted to 20% SDS in summer, 91% reacted in the winter. However, in both studies, substantial inter-individual variations in response to SDS dominated the pattern of response. When designing a human patch test to discriminate skin irritant substances from those that are of minimal effect, it is this inter-individual variability, rather than any small inter-ethnic or seasonal variation, which must be taken into account. This can be achieved by the routine inclusion of a suitable positive irritant control, which then calibrates each human volunteer panel.

Skin permeability barrier and occlusion: no delay of repair in irritated human skin

It has been reported that occlusive treatment of irritated skin results in a reduction of barrier repair activities in hairless mice. In contrast, the clinically observed benefit of occlusion in the treatment of hand eczema and other chronic skin diseases with a perturbed barrier function is well-known. While the beneficial effect of occlusion has been proven for the treatment of psoriasis there are no controlled clinical studies of the effect of occlusion on irritated human skin. We have therefore evaluated the effect of various occlusive treatments on repair of the human skin permeability barrier under controlled experimental conditions. Barrier perturbation was induced either by application of sodium lauryl sulfate (SLS) or by repeated tape stripping. This was followed by treatment with different occlusive and semipermeable dressings, partly after pre-treatment with petrolatum. Repair of water barrier function was evaluated by daily measurements of transepidermal water loss (TEWL) for 1 week. SLS irritation and tape stripping led to a 6-fold increase in TEWL as a sign of severe water barrier perturbation, followed by a stepwise decrease over the following days. Occlusion did not significantly delay barrier repair as measured by TEWL. Only in tape-stripped skin did TEWL stay at high levels during treatment with self-adhesive dressings. This may be explained by damage of newly formed stratum corneum caused by changing of these membranes. Our results indicate that, in contrast to earlier observations in hairless mouse skin, permeability barrier repair activities are not significantly delayed by occlusive treatment in human skin.

Guidelines for measurement of skin colour and erythema. A report from the Standardization Group of the European Society of Contact Dermatitis

This report reviews individual-related variables (age, sex, race, anatomical site, skin surface properties), intra- and interindividual variation (temporal, physical and mental activity, orthostatic effect, menstrual cycle/menopause), environment-related variables (light conditions, temperature) and various instrument-related variables that influence skin colour. CIE colorimetry (Minolta Chroma Meter) and spectrophotometric measurement (Derma Spectrometer) are considered. The guidelines give recommendations for measuring conditions and procedures.

Skin surface lipid and skin friction: relation to age, sex and anatomical region

Differences in the skin surface lipid content (SSL) and the dynamic friction coefficient (mu) were investigated with respect to age, sex, and anatomical region in 29 volunteers. The group consisted of (a) 7 young adult females (24.9 +/- 1.1 years old, mean +/- SD), (b) 7 old females (75.3 +/- 2.4 years old), (c) 7 young adult males (28.7 +/- 0.5 years old), and (d) 8 old males (73.8 +/- 1.9 years old). Measurements were obtained on 11 anatomical regions, namely, the forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper and lower back, thigh, and ankle. Skin surface lipid content data were compared with mu measurements to determine the relative contribution of the former to frictional properties of skin. mu and SSL were not statistically different between age groups on all regions except for the ankle, where lipid content was lower in the elderly. Similarly, mu did not vary between sex groups. Skin surface lipid content was statistically lower on the forehead, dorsal forearm and postauricular area in females. Both parameters, however, showed considerable regional variability. A significant linear correlation was established between mu and SSL combining all regions from all volunteers. When mu was plotted against SSL among individual anatomic sites, only the forehead and postauricular area showed significant linear correlations between the two parameters. These data suggest that surface lipid content plays a limited role in frictional properties of skin.

Surfactant-induced skin irritation and skin repair: evaluation of a cumulative human irritation model by noninvasive techniques

BACKGROUND

Although surfactant-induced acute irritant dermatitis has been extensively studied, our understanding about the induction and repair of the clinically more relevant chronic form is limited.

OBJECTIVE

Our purpose was to investigate qualitative and quantitative differences in surfactant-induced irritant skin reactions from cumulative exposure to structurally unrelated surfactants and to compare the maximal irritant responses from this model with corresponding reactions noted in a previously reported acute irritation model.

METHODS

Sodium lauryl sulfate (SLS), dodecyl trimethyl ammonium bromide (DTAB), and potassium soap were the model irritants. Surfactant solutions (7.5%) were applied for 20 minutes daily (for 8 consecutive days excluding the weekend) to the volar aspect of the forearm of 11 volunteers. Irritant reactions were repeatedly assessed until complete healing was indicated by visual assessment and by measurements of transepidermal water loss (TEWL), erythema (skin color reflectance), and stratum corneum hydration (electrical capacitance). Maximum irritant responses were compared with corresponding reactions from an acute irritation model.

RESULTS

TEWL was increased by SLS and DTAB to the same extent, but erythema was significantly higher in DTAB-treated skin. Skin dryness, as demonstrated by decreased capacitance values and increased scores for scaling and fissuring, was significantly more pronounced than in an acute irritation model for SLS and DTAB, although no difference was detected between the two surfactants. Potassium soap led to a slight increase in TEWL, whereas the remaining features were not significantly changed.

CONCLUSION

This chronic irritation model appears to represent the clinical situation of irritant contact dermatitis with pronounced skin dryness more closely than the acute irritation model. The present study confirms that an extended time is needed for complete healing of irritant skin reactions. We also demonstrated that the evaluation of the irritation potential of diverse surfactants depended significantly on the feature evaluated (erythema vs electrical capacitance and TEWL), on the mode of application (acute vs cumulative), and, in the cumulative model, on the point of observation.

Surfactant-induced skin irritation and skin repair. Evaluation of the acute human irritation model by noninvasive techniques

BACKGROUND

Although the induction of irritant dermatitis by surfactants has been extensively studied in recent years, our understanding of the repair phase of irritant dermatitis is limited.

OBJECTIVE

We investigated qualitative and quantitative differences in surfactant-induced irritant skin reactions from short-term exposure to three structurally different surfactants.

METHODS

Sodium lauryl sulfate (SLS), dodecyl trimethyl ammonium bromide (DTAB), and potassium soap were the model irritants. Surfactant solutions (0.5%) were applied for 24 hours to the volar aspect of the forearm of 11 volunteers. Irritant reactions were assessed until complete healing was indicated by visual assessment and by various aspects of skin function, that is, transepidermal water loss (TEWL), erythema (skin color reflectance), and stratum that is, transepidermal water loss (TEWL), erythema (skin color reflectance), and stratum corneum hydration (electrical capacitance).

RESULTS

SLS and DTAB induced similar degrees of erythema, whereas SLS induced significantly higher TEWL increase. Although both erythema and TEWL were highest 1 hour after exposure to surfactants, skin dryness was a symptom with delayed onset, justifying the long observation period in this study. Minimum hydration values were measured as late as 7 days after surfactant exposure. Dryness was significantly more pronounced in areas exposed to SLS than in areas exposed to DTAB. Complete repair of the irritant reaction induced by either SLS or DTAB was achieved 17 days after surfactant exposure. Stratum corneum hydration was the last feature to return to baseline values. Potassium soap did not significantly influence any skin function.

CONCLUSION

We emphasize the importance of extended periods needed before a patient with irritant contact dermatitis can be reexposed to irritant substances. The evaluation of the irritation potential of diverse surfactants depended significantly on the feature (erythema vs hydration and TEWL) measured.

Determination of acitretin in the skin, in the suction blister, and in plasma of human volunteers after multiple oral dosing

Several HPLC methods for quantification of acitretin and its 13-cis isomer in biological fluids have been described. Only limited data are available on determination of this drug in skin samples. Our objective was to improve the sensitivity and selectivity of existing methods to measure drug in small skin samples from humans treated with acitretin. With a new optimized mobile phase [methanol: acetonitrile (7:3, v/v), purified water with 1.5% (v/v) acetic acid, mixed in a 85:15 ratio (v/v)] and a new internal standard (arotinoid ethyl sulfone), a limit of quantification of 1 ng/g tissue was reached. Nine male volunteers were given an oral daily dose of 50 mg acitretin for up to 28 days. Blood and skin samples (punch and shave biopsies, suction blister skin, and fluid) were taken at various time points during and after treatment. Drug concentration and metabolism in plasma and skin samples appeared to be linked in that the trans-isomer concentration was always higher than the cis-isomer concentration during dosing and 3 h after the last dose. However, 7 and 14 days after the last dose in plasma and in all tissue samples (except the shave biopsy), the all-trans-acitretin concentration rapidly decreased and approached the detection limit. In the shave biopsy, the all-trans-acitretin concentration remained higher than the 13-cis-acitretin concentration. Furthermore, the elimination of two isomers from the shave biopsy was delayed.(ABSTRACT TRUNCATED AT 250 WORDS)

[Penicillamine-induced elastosis perforans serpiginosa]

Elastosis perforans serpiginosa is a rare disease with variable etiology. We report on a 33-year-old male patient in whom the disease was induced by long-term treatment with the chelating agent D-penicillamine.

[Hibernoma of the forehead. A rare tumor of brown fatty tissue in an unusual site]

We report a hibernoma located on the forehead in a 52-year-old female patient. The hibernoma is a rare tumour derived from brown adipose tissue. Location on the forehead is unusual and has not been reported before.

Surfactant-induced stratum corneum hydration in vivo: prediction of the irritation potential of anionic surfactants

After repeated contact, many surfactants will cause skin irritation and, especially, dryness and scaliness. Earlier in vitro investigations suggested that the irritation potential of anionic surfactants was related to the induction of hydration of isolated stratum corneum membranes. We have now investigated early surfactant-stratum corneum interaction in vivo. Sodium salts of n-alkyl sulfates with variable carbon chain length (n = 8-14) were tested for the promotion of stratum corneum hydration by measurements of skin surface water loss and electrical capacitance measurements in healthy adult human volunteers. The surfactant-induced increase in water uptake was confirmed in vitro by means of isolated stratum corneum samples and surfactant solutions labeled with tritiated water. In a parallel experiment the irritation potential of these compounds was investigated by 24-h patch testing in human volunteers. The irritant responses were quantified non-invasively by erythema (skin color reflectance measurements) and transepidermal water loss measurements. Hydration of stratum corneum exposed for 5 min to surfactant solutions significantly exceeded that of controls (phosphate-buffered saline). It increased with application time and was concentration dependent, saturable with increasing concentration, and rapidly reversible. Baseline hydration was re-established only 10-15 min after treatment termination. Induction of hydration was closely correlated with the irritation potential of the investigated compounds. It initially increased with increasing carbon chain length. The maximum response was obtained for the C12 analogue (sodium lauryl sulfate). With further increases in molecular size induction of stratum corneum hydration subsequently decreased. We have demonstrated that anionic surfactants increase stratum corneum hydration in vivo. The present results suggest that the mechanisms responsible for the hydration are related to the irritation properties of these compounds.

In vivo skin penetration of acitretin in volunteers using three sampling techniques

Etretinate and acitretin are given orally to treat psoriasis and various keratinization disorders. Acitretin, the main active metabolite of etretinate, has the pharmacokinetic advantage of being rapidly eliminated, but it shares etretinate's toxicologic profile. Thus a topical delivery of acitretin with no or reduced systemic adverse effects is desirable. To characterize the therapeutic potential of topically delivered acitretin, we quantitatively assessed its percutaneous penetration in healthy human volunteers. Additionally, three skin sampling techniques, the punch biopsy, the shave biopsy, and the suction blister technique, were validated to quantitate acitretin in the skin. The results suggest that topical delivery of acitretin renders skin concentrations which exceed those reported after oral administration of etretinate or acitretin. However, because of possible interlaminate drug contamination, drug localization within a particular skin compartment cannot be determined.

In vivo percutaneous absorption of [14C]acitretin in the hairless guinea pig and in the rhesus monkey

The oral administration of retinoids such as etretinate and acitretin (Ro 10-1670, CAS 55079-83-9), provides a successful therapeutic approach in various cutaneous diseases characterized by disturbed keratinization, e.g. psoriasis. Nevertheless oral therapy is often associated with systemic adverse effects. This makes a topical form with no or reduced systemic side effects desirable. Direct application of a topical acitretin formulation to the skin might result in therapeutic skin concentrations while minimizing systemic exposure. In the hairless guinea pig and in the rhesus monkey the percutaneous absorption of [14C]acitretin from an isopropylmyristate formulation (160 micrograms acitretin/2.5 cm2/animal) were investigated in vivo. After a 24 h exposure drug concentration in the skin was higher in the hairless guinea pig (620 ng-eq/g wet tissue) than in the rhesus monkey (380 ng-eq/g wet tissue). A similar observation was made comparing the 24 h absorption data determined as amount of drug excreted. The results are compared with in vitro absorption data using skin from the same species.

In-vitro skin pharmacokinetics of acitretin: percutaneous absorption studies in intact and modified skin from three different species using different receptor solutions

The aromatic synthetic retinoid acid derivative, acitretin, is efficacious in several cutaneous diseases. Its toxicological profile makes a topical form with no or reduced systemic adverse effects desirable. Direct application of a topical acitretin formulation might result in therapeutic skin concentrations at the site of the disease while minimizing systemic exposure. The present studies define the percutaneous absorption characteristics of acitretin from an isopropylmyristate formulation. We investigated, in-vitro, (1) the role of receptor solution variations, (2) the role of skin modifications, (3) the influence of skin from three different species on the absorption of topically applied acitretin and (4) the drug distribution within the skin. Addition of solubilizers (Polyethylenglycol-20 and albumin) to the receptor solutions improved the flux of acitretin through monkey skin, whereas the acitretin concentration in the skin was not affected by the various receptor solutions used. Acitretin flux through tape-stripped monkey skin and dermis was only slightly higher than through intact skin. Acitretin concentration in human skin was significantly higher than in rhesus monkey or guinea-pig skin. Topical application of acitretin can produce dermal concentrations in excess of those achieved by therapeutic oral doses.

Skin aging. Effect on transepidermal water loss, stratum corneum hydration, skin surface pH, and casual sebum content

This study investigates the effect of cutaneous aging on transepidermal water loss, stratum corneum hydration (capacitance), skin surface pH, and causal sebum content. Because the physiologic condition of skin varies considerably with anatomic region and skin aging might demonstrate regional variability, all factors were studied on 11 anatomic locations in 14 young adult (seven female and seven male subjects; 26.7 +/- 2.8 years [mean +/- SD]) and 15 aged human volunteers (seven female and seven male subjects; 70.5 +/- 13.8 years). Significant anatomic variability was noted for all factors in both age groups. However, no significant differences between the two groups were noted for sebum, capacitance, and pH on most anatomic regions. Transepidermal water loss, however, was significantly lower in the aged population on all anatomic regions tested, except for the postauricular region and the palm. Comparing male and female volunteers, none of the four factors showed significant differences. Of all measured factors, only transepidermal water loss showed significant age-related differences on most anatomic regions studied. The additionally observed differences between the age groups on the ankle for pH and sebum might be related to the stasis frequently observed on the lower limbs in aged individuals.

Effect of sodium lauryl sulfate-induced skin irritation on in vivo percutaneous penetration of four drugs

The influence of sodium lauryl sulfate-induced irritant contact dermatitis on in vivo percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment, 450 microliters saturated solutions of HC, IM, IB, or AC in isopropylmyristate were applied to the pretreated skin for 24 h. Systemic absorption was determined by urinary and fecal excretion of compounds. Drug concentrations in stratum corneum (obtained by tape cellophane stripping after decontamination of the application site) and in epidermis/dermis (punch biopsy) were also investigated. Systemic absorption of topically applied drugs (as evaluated by urinary and fecal excretion) in SLS-irritated skin was significantly increased for HC (factor 2.6) followed by IB (1.9 times) and IM (1.6 times) but not increased for AC. However, drug concentrations in the viable epidermis and dermis were 70% lower in SLS-irritated than normal skin for HC, but not different for IB, IM, and AC. Thus, the influence of the state of the skin (irritant dermatitis versus healthy) on percutaneous penetration was different for diverse drugs. The general assumption that percutaneous penetration and drug tissue concentrations were higher in diseased versus healthy skin was not found to be true in our irritated-skin model.

Effect of sodium lauryl sulfate-induced skin irritation on in vitro percutaneous absorption of four drugs

The influence of irritant contact dermatitis on percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated in vivo for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment animals were sacrificed. Percutaneous penetration was then measured using in vitro diffusion cells and the removed (pretreated) skin. The following parameters were determined: cumulative amount of compound penetrated, steady state flux, lag time, and permeability coefficient, skin concentration per unit area, and the relative amount of drug remaining in the skin (as a percentage of the cumulative amount of compound penetrated through the skin). SLS pretreatment resulted in moderate irritant dermatitis in all animals and increased in vivo transepidermal water loss 4.5 times. Flux was increased in SLS-pretreated skin as compared with controls for all four compounds, with the greatest enhancement for hydrocortisone (HC) (5.9 times), followed by indomethacin (IM) (4.6 times), ibuprofen (IB) (3.9 times), and acitretin (AC) (3.4 times). Skin concentrations increased to a smaller degree from 1.6 times (IB) and 2.6 times (HC) to 3.4 times (IM). However, AC skin concentrations were not different between the two groups. Thus, percutaneous penetration parameters were equivocally influenced by SLS-induced irritation. Increased skin concentrations were paralleled by even higher increases in flux.

Optimization of topical therapy: partitioning of drugs into stratum corneum

To optimize a topical formulation for therapeutic effect generally implies that the flux of drug into the skin be maximized. This requirement means that the product of drug concentration in the vehicle (Cv) and drug partition coefficient (PC) between stratum corneum (SC) and vehicle be as large as possible. While Cv is a formulation variable which can be easily manipulated up to the drug's saturation solubility, PC is a parameter that is difficult to predict a priori. However, there is no question that an ability to evaluate PC would greatly facilitate the efficient screening of drugs and formulations. We have measured the SC/water and SC/isopropylmyristate (a model lipophilic vehicle) PCs of seven drugs; acitretin, progesterone, testosterone, diazepam, estradiol, hydrocortisone, and caffeine, SC/water PCs were determined as a function of the following variables: (i) initial drug concentration in the vehicle, (ii) length of equilibrium, (iii) SC source and preparation technique, and (iv) SC delipidization. The data obtained were reproducible and physicochemically consistent, and they show that useful partitioning information from both aqueous and nonaqueous vehicles can be obtained with the biological tissue of greatest relevance. The SC/water PCs of the steroids were in reasonable agreement with previous measurements. A facile approach to an integral determinant of formulation optimization is suggested, therefore, by these observations.

Cutaneous sodium lauryl sulphate irritation potential: age and regional variability

To investigate differences in response to irritation according to age and site seven young-adult and eight elderly females were exposed to 0.25% sodium lauryl sulphate (SLS) under patch-test occlusion for 24 h. Ten anatomical regions were tested: forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper back, thigh, and ankle. The skin responses were evaluated 24 h post-patch removal by visual scoring and by transepidermal water loss measurements (TEWL). Non-treated symmetrical anatomical regions served as controls. SLS induced a mild erythematous reaction on most anatomical regions except the palm and TEWL was significantly increased as compared with controls. The elderly group demonstrated significantly less susceptibility to SLS-induced irritation for most regions of the body as indicated by visual scores and TEWL measurements. In addition, evaluation of the stratum corneum water content following SLS irritation demonstrated lower responses in the old age group for most regions. The thigh had the highest reactivity and the palm the lowest, in both age groups. These data suggest that young adult skin is more sensitive to SLS than old skin and that SLS irritation varies considerably with respect to region. Moreover, objective TEWL measurements seem to be a better indicator of irritant susceptibility, especially in the elderly, than clinical evaluation by visual scoring.

Irritation factors of sodium hypochlorite solutions in human skin

The recommended concentration for patch testing with sodium hypochlorite [NaOCl] (bleach) is 1%, generally obtained by diluting commercial bleach. In doing so, other active (potentially irritant) components of bleach, especially hypochlorous acid [HOCl] and sodium hydroxide [NaOH], are neglected. Magnitudes of potential irritant species other than NaOCl, such as alkalinity, are ordinarily not labeled on the product, though they may vary considerably between brands. Thus, patch testing with 1% hypochlorite obtained by diluting different brand bleaches can potentially elicit non-specific irritant responses, also depending upon the test volume applied. In this study, skin irritation induced by 24-h patch testing with 20 microliters or 100 microliters, with constant NaOCl concentration (1%) and different NaOH concentrations (0.01-1.0%), was studied in adult human volunteers, by means of visual scores and skin color reflectance measurements. No irritation was elicited by application of 20 microliters 1% OCl-, independent of the NaOH concentration. However, all solutions induced significant irritation in a volume of 100 microliters. Skin reactions did not show a straight pH dose response, a maximum reaction being seen to the solution containing 0.1% NaOH. Skin surface pH values had increased when monitored immediately after removal of the patch material. However, 24 h later, baseline values were again reached at most sites, demonstrating an efficient buffering capacity of human skin, even after challenge with alkaline solutions of pH 13.4. We suggest that a non-irritant concentration for diagnostic patch testing for allergic contact dermatitis with an aluminum chamber, using 17 microliters to 20 microliters test volume, could be as high as 1% NaOCl and 1% NaOH.

Frictional properties of human skin: relation to age, sex and anatomical region, stratum corneum hydration and transepidermal water loss

Differences in the dynamic skin friction coefficients (mu) were investigated with respect to age, sex, and anatomical region. A total of 29 volunteers consisting of seven young females, seven old females, seven young males, and eight old males participated in the study. Measurements were obtained from II anatomical regions, namely, the forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper and lower back, thigh, and ankle. The friction data were compared with stratum corneum hydration and transepidermal water loss (TEWL). The dynamic friction coefficient did not vary significantly between age and sex groups but varied considerably among the anatomical regions of the body. The forehead and postauricular had the highest mu (0.34 +/- 0.02) while the abdomen had the lowest (0.12 +/- 0.01); the remaining regions had an average mu value of 0.21 +/- 0.01. Similarly, no sex differences were observed for TEWL and stratum corneum hydration. Capacitance was only significantly lower on the palms of the elderly. Regional differences showed a higher state of hydration on the forehead and postauricular as well as the upper arm, upper and lower back when compared with the volar forearm. TEWL was generally lower in the elderly on all anatomical regions except the postauricular and palm. A significant correlation was established between mu and capacitance for most regions. Between mu and TEWL significant correlation was observed only on the palm and thigh. These findings suggest that frictional properties of skin are dependent on more than water content or non-apparent sweating and the role of sebum secretion is suggested as one possible factor.

Elastic properties of human skin: relation to age, sex, and anatomical region

Using a recently developed noninvasive, in vivo suction device for measuring skin elasticity, we evaluated age, sex, and regional differences in the viscoelastic properties of skin. A total of 33 volunteers participated in the study consisting of (a) 8 young females, (b) 9 old females, (c) 8 young males and (d) 8 old males. Measurements were performed on 11 anatomical regions; three different loads were applied: 100, 200, and 500 mbar. The parameters used were: immediate distension (Ue); delayed distension (Uv); immediate retraction (Ur); and, final deformation (Uf). To compare between subjects and anatomical regions, relative parameters independent of skin thickness were calculated: Uv/Ue, the ratio between the viscoelastic properties of skin and immediate distension, and Ur/Uf, which measures the ability of the skin to regain its initial position after deformation. Generally, Uv/Ue increased while Ur/Uf decreased with aging. Responses were variable with respect to load applied. Variability within anatomical regions was also noted. However, differences between the sexes were not statistically significant for most regions. These findings are in congruence with earlier studies suggesting the differences are mainly attributable to alterations in the elastic fiber network. This procedure provides a simple, quantitative assessment of elastic properties of the skin. Its application may help in future investigations of other connective tissue disorders.

Partitioning of chemicals into human stratum corneum: implications for risk assessment following dermal exposure

Assessment of the health hazard associated with chemical contamination of the skin is a complex problem of occupational and environmental relevance. A particularly important question is to what extent can the skin permeability of a given compound be predicted from simple experiments. The literature on percutaneous absorption identifies two key observations: (i) the stratum corneum (SC), the skin's outermost layer, is the major barrier to chemical transport, and (ii) there are qualitative correlations between penetrant permeability and various oil/water partition coefficients (PCs). To obtain more quantitative predictions of permeation, we have evaluated SC/water and SC/isopropyl myristate (IPM, a model lipophilic vehicle) PCs of (a) para-substituted phenols of diverse physicochemical properties (4-acetamido-, 4-cyano-, 4-iodo-, and 4-pentyloxyphenol), (b) polychlorinated biphenyls (54%), and (c) 1,1,1,-trichloro-2,2-bis(p-chlorophenyl)ethane. Partition coefficients were determined as a function of the following variables: length of equilibration, initial drug concentration in the vehicle, SC delipidization, and SC source and preparation technique. The data demonstrate that reproducible partitioning can be obtained using the biological tissue of greatest relevance, and that the pattern of behavior observed, for the two different vehicles studied, is compatible with physicochemical expectations. We suggest that the PC values measured may be useful predictors of in vitro and in vivo skin transport and valuable assets, therefore, in the evaluation of risk following dermal exposure.

Increased stratum corneum turnover induced by subclinical irritant dermatitis

The chronic effects of the irritant sodium lauryl sulphate (SLS) on stratum corneum (SC) barrier function, determined by transepidermal water loss (TEWL) measurements and on epidermal cell kinetics, estimated by stratum corneum turnover time (SCTT) determination (dansyl chloride staining method), were investigated in 18 healthy female volunteers. SLS (7.5%) was applied without occlusion for 20 min once daily, over a period of 3 weeks (5 days a week) on dansyl chloride-stained skin and on untreated skin. SCTT of untreated skin (19.3 +/- 0.8 days; mean +/- SEM) was not changed by daily treatment with water (control) (19.3 +/- 2.0) but was significantly reduced by SLS (10.9 +/- 0.6; P less than or equal to 0.0001; compared to controls). However, TEWL was increased in SLS-treated sites 1.5-fold after 4 days of treatment (5.3 +/- 0.6 vs. 3.5 +/- 0.3; P less than 0.001). At the end of the second week, TEWL was increased 2.6-fold and after 3 weeks TEWL was 3.3 times higher than in controls 13.0 +/- 1.6 vs. 3.9, P less than or equal to 0.0001). The intensity of SLS-induced irritation as measured by TEWL was significantly correlated with baseline TEWL (r = 0.50; P less than or equal to 0.02) and significantly negatively correlated with SCTT of SLS treated sites (r = -50; P less than or equal to 0.02) but not with SCTT of untreated skin (r = 0.19).

Factors predisposing to cutaneous irritation

In experimental skin toxicology, as well as in clinical practice, considerable interindividual variation in the susceptibility to irritant dermatitis is noted when irritant doses are low. Cutaneous sensitivity and hypersensitivity are not determined by a single known feature but are multifactorial. Previous atopic dermatitis may predispose to irritant dermatitis. Susceptibility to irritation seems to be influenced by age, race, and genetic background, whereas sex-related differences do not seem to exist. Of biophysical skin baseline features, skin-surface pH was correlated with the severity of experimentally induced irritant dermatitis, but baseline transepidermal water loss, water-holding capacity, stratum corneum turnover time, and sebum content were not.

Enhanced in vivo-lipid peroxidation associated with halothane hepatotoxicity in rats

To study the role of lipid peroxidation in halothane-induced hepatic damage, ethane exhalation by rats exposed to 1% halothane for 1 hour was determined under normoxic (21% O2) and hypoxic (6% O2) conditions. The effects of microsomal enzyme induction by phenobarbital and/or glutathione depletion on this parameter of in vivo lipid peroxidation were studied. To assess the degree of liver damage, serum activities of liver specific enzymes (glutamate-pyruvate-transaminase, GPT, and sorbitol dehydrogenase, SDH) were measured 3 hrs after the end of exposure. Besides, liver content of thiobarbituric acid-reactive material was estimated as a further parameter of lipid peroxidation. Enhanced rates of lipid peroxidation over basal levels were only seen under conditions leading to hepatic damage, i.e. phenobarbital induction and hypoxia. The highest rate of lipid peroxidation was observed after depletion of hepatic glutathione in addition to microsomal enzyme induction and hypoxia. Deferrioxamine, diethyldithiocarbamate and (+)-catechin inhibited in vivo lipid peroxidation, but only (+)-catechin suppressed halothane-hepatoxicity. These results indicate that halothane-induced hepatic damage is associated with an enhanced rate of lipid peroxidation, but this might not be the only mechanism of halothane toxicity.

Halothane hepatotoxicity in glutathione depleted rats

Experimental models for halothane hepatotoxicity require microsomal enzyme induction by phenobarbital or triiodo-thyronine pretreatment and hypoxic conditions. The role of GSH in the metabolism of halothane, however, is still unclear. We therefore pretreated male rats with phorone to deplete hepatic GSH, phenobarbital as a microsomal enzyme inducer and exposed them to halothane 1% for 4 h under hypoxia (10% O2). Increases in serum enzyme activities of alanine aminotransferase (GPT) and sorbitol dehydrogenase (SDH) were observed 24 and 48 h later. Histomorphological examinations showed centrilobular hepatic necrosis. In GSH-depleted rats the increments of serum enzyme activities and histomorphological alterations were significantly aggravated as compared with controls. In this model (+)-catechin protected against halothane-induced hepatotoxicity as evidenced by reduced serum enzyme elevations and morphological alterations whereas diethyldithiocarbamate failed to exert any protective effects. Free fluoride concentrations in plasma was used as an index of the non-oxidative defluorination of halothane. Increased plasma fluoride levels were observed under conditions which evoked hepatotoxicity but did not correlate with the protective effect of (+)-catechin. Our experimental data indicate that glutathione might be involved in the non-oxidative metabolic pathways of halothane. Furthermore, (+)-catechin seems capable of protecting against the direct toxic effect of halothane metabolites resulting from the reductive pathways.

Sodium hydroxide-induced subclinical irritation. A test for evaluating stratum corneum barrier function

This report concerns the development of a short, simple, non-invasive test for assessing sensitivity to irritant dermatitis. Application of NaOH (0.005-2.0 mol/l) to human skin resulted in significantly greater skin surface water loss directly after exposure (1-15 min) than of control (water). The increase in skin surface water loss after NaOH application was dose-dependent (0.005-0.1 mol/l) and application time-dependent (1-10 min). Application times exceeding 10 min did not further increase skin surface water loss and doses higher than 0.1 mol/l reversed the effect on skin surface water loss. 15 min after removal of the alkali, skin surface water loss baseline values were almost regained. This procedure did not cause visible reactions or discomfort for the volunteers. In a subsequent experiment, volunteers were exposed to 0.2 mol/l NaOH for 5 min on one forearm and to 1% sodium lauryl sulfate for 24 h contralaterally. Skin surface water loss after 5 min of NaOH application was significantly correlated with transepidermal water loss measurements after 24 h of sodium lauryl sulfate patch application. This is, to our knowledge, the first description of a procedure for quantifying interindividual differences in stratum corneum barrier function without inducing visible changes or causing volunteers discomfort. Use of this model should help to further investigate skin barrier function as well as to test protective devices and barrier creams.