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).

Sunscreening agent intolerance: contact and photocontact sensitization and contact urticaria

Reports in the literature of sensitization associated with many commonly used sunscreening agents including p-aminobenzoic acid (PABA), PABA derivatives, anthranilates, salicylates, cinnamates, benzophenones, and dibenzoylmethane derivatives are reviewed. Several of these case reports involved subjects with various photodermatoses, implicating enhanced sensitivity of the patient's skin to both light and chemicals. Despite the widespread use of sunscreens, the small number of published reports of contact and photocontact sensitization to these agents suggests that either such sensitization is less than commonly perceived or is underreported. Establishment of a registry for reporting adverse effects associated with sunscreening agents would help to characterize the incidence of sensitization.

Methylchloroisothiazolinone-methylisothiazolinone reactions in patients screened for vehicle and preservative hypersensitivity

More than 1100 patients were tested with methylchloroisothiazolinone-methylisothiazolinone, 100 ppm, in aqueous and petrolatum-based patch test materials from 1985 to 1987 by members of the North American Contact Dermatitis Group. Thirteen reactions to the aqueous materials and 10 to the petrolatum-based materials were observed. Irritant reactions were infrequent, and about half the reactions were deemed relevant. From 1984 to 1985, patch tests with this substance at a concentration of 250 ppm in petrolatum were conducted. Thirteen persons were identified as allergic, but three others were sensitized by the patch test procedure. Sensitization as not observed in tests with aqueous or petrolatum-based substance at a concentration of 100 ppm, and this concentration appears to be the best compromise between safety and sensitive detection of allergy. Use tests are helpful but not infallible as a guide in establishing relevance with methylchloroisothiazolinone-methylisothiazolinone. Wash-off products are frequently well tolerated by patients with positive reactions to this substance.

A functional study of the skin barrier to evaporative water loss by means of repeated cellophane-tape stripping

The functional role of different layers of the horny layer in preventing evaporative water loss was studied by an adhesive cellophane-tape stripping technique. The increase in transepidermal water loss, as described by a mathematical equation based on curve-fitting analysis, was shown to be proportional to the decrease in thickness of the horny layer. In the second half of the curve the experimental data showed slightly higher transepidermal-water-loss values than would be expected on the basis of proportionality with thickness of the stratum corneum. The data suggest that the outer layers of the horny layer are also important in forming a barrier to evaporative water loss.

Adverse dermatologic reactions to transdermal drug delivery systems

Transdermal drug delivery systems are marketed in the United States for four different drugs, and others are in various stages of development. Cutaneous side effects occur frequently with these systems and sometimes necessitate discontinuation of therapy. This article will review these adverse reactions.

In vivo percutaneous absorption of fragrance ingredients in rhesus monkeys and humans

The percutaneous absorption of the fragrance diethyl maleate was measured in vivo in human and monkey studies. With the application sites occluded, 54% of the applied dose of the volatile fragrance penetrated human skin in 24 hr compared with 69% absorption in the monkey skin. It was concluded that the monkey is a good model for human skin with regard to the penetration of this fragrance material since no significant difference in the absorption of diethyl maleate was observed. The percutaneous absorption of the fragrances benzyl acetate and five other benzyl derivatives (benzyl alcohol, benzyl benzoate, benzamide, benzoin and benzophenone) was determined in vivo in monkeys. Absorption through occluded skin was high for all compounds (approximately 70% of the applied dose in 24 hr) and no significant differences between the values for the different compounds were observed. No correlations were seen between skin penetration of these compounds and their octanol-water partition coefficients. Under unoccluded conditions skin penetration of the fragrances was reduced and there was great variability between compounds, presumably because of variations in the rates of evaporation from the site of application. The data suggest that humans may have significant systemic exposure to these fragrance materials.

Mechanical properties of human forearm and vulvar skin

Using a newly developed suction device, the mechanical properties of forearm and vulvar skin were studied in 22 healthy women, 12 before and 10 after the menopause. The ratio between viscous deformation (Uv) and elastic deformation (Ue) and the biological elasticity, i.e. the ratio between immediate recovery (Ur) and total deformation (Uf), were both significantly lower in vulvar than in forearm skin. Ur/Uf decreased significantly with load in vulvar, but not in forearm skin, whereas Uv/Ue was not load-dependent in either site. Uv/Ue remained constant with age in both test sites, whereas Ur/Uf was significantly lower in post-menopausal women in both forearm and vulvar skin. In vulvar, but not in forearm skin, Uv/Ue was significantly correlated with body height which may be an indicator of mechanical connective tissue properties. Viscous deformation plays a lesser role and biological elasticity is decreased in vulvar compared to forearm skin. Despite differences in mechanical parameters at both sites, age-related changes seem to be similar.

Dermal absorption of the phenoxy herbicides 2,4-D, 2,4-D amine, 2,4-D isooctyl, and 2,4,5-T in rabbits, rats, rhesus monkeys, and humans: a cross-species comparison

Dermal absorption of the 14C-ring-labeled phenoxy herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4-D amine (2,4-dichlorophenoxyacetic acid dimethylamine), 2,4-D isooctyl (2,4-dichlorophenoxyacetic acid isooctyl ester), and 2,4,5-T amine (2,4,5-trichlorophenoxyacetic acid trimethylamine) was examined following topical applications of the herbicides to the back of rabbits, the back and tail of rats, the forearm and forehead of rhesus monkeys, and the forehead of human volunteers. The effect of three pesticide vehicles (water, acetone, and Esteron LV96) was also investigated. The total percent dermal absorption was calculated from the mean percent urinary recoveries from the animal tests and corrected for nonurinary excretion of the radiolabel using data from intramuscular (im) injections. The human data are reported without im correction. The reliability of animal data for modelling human dermal absorption of pesticides is highlighted.

Monitoring the water-holding capacity in visually non-irritated skin by plastic occlusion stress test (POST)

Skin-surface water loss (SSWL) and transepidermal water loss (TEWL) were studied after a plastic occlusion stress test (POST) in visually non-damaged skin treated with 7% sodium lauryl sulphate for 3 days (open application). After removal of the 24-h plastic occlusion, SSWL and TEWL were recorded continuously for 25 min. SSWL decay curves show significant differences between control and treated areas. The total amount of water trapped within the stratum corneum and released after 1 min is significantly reduced (P less than 0.01) in the treated site. Higher TEWL (P less than 0.02) in visually non-irritated skin is noticeable in the terminal part of the curve reflecting the damage of the water barrier in irritated skin. The data suggest that clinically normal skin exposed to subliminal irritant stimuli is less capable of storing water within the stratum corneum resulting in decreased hydration. The POST appears to be a simple and reliable tool to investigate non-visible but biologically relevant changes in stratum corneum function.

Transepidermal water loss and skin surface hydration in the non invasive assessment of stratum corneum function

Transepidermal water loss (TEWL) and water content of the stratum corneum, when measured simultaneously, provide important information regarding skin function. On the basis of the model presented, it is possible to differentiate dry senile skin from dry pathological skin (such as psoriasis, atopic dermatitis, irritant reaction), clinically involved or uninvolved. Pathological dry skin, because of the impaired barrier function is associated with increased TEWL and low corneum water content. Senile skin, on the other hand, shows both, decreased TEWL and stratum corneum water content. It is suggested that with this model it may be possible to differentiate uninvolved pathologic from healthy skin.

Pharmacodynamic measurements of methyl nicotinate percutaneous absorption: the effect of aging on microcirculation

The penetration of drugs through aged skin is important both in terms of transdermal delivery to elicit systemic pharmacological effects, and for topical treatment. Cutaneous microcirculation efficiency, an integral parameter in the overall process of percutaneous absorption, was studied in young (20-34 years) and old (64-86 years) individuals. Cutaneous erythema as induced by topical administration of methyl nicotinate to the ventral forearm, was monitored non-invasively using laser-Doppler flowmetry. Dose-response behaviour was characterized by five parameters: (i) the time of onset of action; (ii) the time to reach maximum response; (iii) the magnitude of the maximum response; (iv) the area under the response-time curve; and (v) the time to decay to 75% of the maximum response. Additionally, the sensitivity and efficiency of the cutaneous microcirculation in both age groups was evaluated using a pharmacokinetic-pharmacodynamic model. Statistical analysis of all data showed no significant differences between the age groups for the same concentrations. The results indicate that microvessel reactivity to the applied stimulus is comparable in the ventral forearm of both young and old populations.

In vivo percutaneous absorption of chemicals: a multiple dose study in rhesus monkeys

The effect of daily topical application on the in vivo percutaneous absorption of benzoic acid, parathion and salicylic acid in rhesus monkeys has been investigated. The study was designed to test further the hypothesis that topical bioavailability, or body burden, of a chemical following chronic exposure may be accurately predicted from the result of a single acute-dose experiment. No significant change in percutaneous absorption from that following the initial dose was observed following the eighth daily dose of a 14-day multidose regimen for each of the three penetrants considered. The results are consistent with those of recent experiments in humans with malathion and steroids, but not entirely consistent with the results of other animal studies.

Transepidermal potassium ion, chloride ion, and water flux across delipidized and cellophane tape-stripped skin

The skin barrier was evaluated as a function of transepidermal water loss (TEWL) and electrolyte loss. Combination electrodes for chloride and pH determinations and a potassium ion electrode were utilized. Delipidization of the skin did not impair the electrolyte barrier, but did damage the epidermal water barrier. Cellophane tape stripping of normal stratum corneum resulted in an increase in outward transepidermal potassium and chloride ion flux, an increase in skin surface pH, and an increase in TEWL. It appears that damage to the epidermal water barrier does not necessarily result in damage to the epidermal electrolyte barrier. We found the potassium electrode facile to use and believe that a combination potassium electrode would be useful for investigating and assessing the epidermal electrolyte barrier.

Idiopathic recalcitrant facial flushing syndrome

This report neologizes a new syndrome name, idiopathic recalcitrant facial flushing syndrome, to describe all cases of persistent facial flushing with unknown etiology. Three cases of recalcitrant flushing are described. Therapy with a variety of modalities, monitored objectively with laser Doppler velocimetry, proved unsuccessful. Some investigational and management aspects of difficult cases of idiopathic flushing are reviewed.

Frictional properties of human forearm and vulvar skin: influence of age and correlation with transepidermal water loss and capacitance

The dynamic friction coefficient between skin and a Teflon probe and its correlation with age, body weight, height, transepidermal water loss and skin capacitance was studied in vulvar and forearm skin of 44 healthy female volunteers. The friction coefficient of vulvar skin was 0.66 +/- 0.03 (mean +/- SEM) compared to that of forearm skin of 0.48 +/- 0.01. The difference was highly significant (p less than 0.001). Multiple-regression analysis showed that the vulvar skin friction coefficient was significantly correlated with capacitance as an indicator of stratum corneum hydration (p less than 0.01) but not with age, weight, height or transepidermal water loss. It is concluded that the high friction coefficient of vulvar skin may be due to the increased hydration of vulvar skin. Age-related differences seem to exist for transepidermal water loss and friction coefficient in forearm but not in vulvar skin.

Diseased skin models in the hairless guinea pig: in vivo percutaneous absorption

We observed hydrocortisone and benzoic acid absorption in relation to experimentally induced in vivo damaged skin models in the hairless guinea pig. Radioactivity of the drugs in urine was calculated as absorbed dose. Both drugs have different patterns of excretion in urine. Damaging the skin abolished some barrier function and increased the absorption of both model drugs. With cellophane-tape-stripped skin, the absorption was increased 3 times and 2 times for each drug, respectively. Irritation with 2% sodium lauryl sulfate increased absorption by a ratio of 2-4 times. Defatting with chloroform/methanol (2:1) mixture increased absorption to the greatest extent (5- and 2.7-fold). The possible mechanism of a delipidization effect was considered in view of a visible skin lesion and inflammatory reaction. Precautions are proposed for those with damaged/diseased skin in dealing with topical medications or handling solvents.

Human cutaneous response to a mixed surfactant system: role of solution phenomena in controlling surfactant irritation

Exposure of the skin to surfactant-based products can result in irritation. To control this effect researchers are probing mechanisms of surfactant action. In vitro studies show that mixing surfactants often results in less denaturation (swelling) of stratum corneum. We have explored the in vivo human irritation response (using a 21-day cumulative irritation test) to two of these surfactants-sodium lauryl sulfate (SLS) and (C12-C14) alkyl, 7-ethoxy sulfate (AEOS-7EO). Results demonstrate that addition of AEOS-7EO to a constant dose of SLS results in a significant reduction in erythema, hence producing a milder system. The reason for the synergism is unclear, but may related to experimentally determined alterations in the micellar solution properties of the SLS upon addition of AEOS-7EO.

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.

Potential for irritation increases from the wrist to the cubital fossa

The effect of site on the irritant dermatitis potential was studied in 10 subjects using the volar surface of the forearm. Erythema scoring and transepidermal water loss (TEWL) measurements were used to assess irritation at different levels on the forearm. A sodium lauryl sulphate (SLS 2 g/v%) solution was used as a standard irritant in a patch test procedure and on open tests. Both the erythema scores and measurements of the TEWL of exposed skin showed significant localization differences, and demonstrated that the same sites on the forearm should be used for irritancy tests and possibly physiological studies.

Differences in the biochemical activity in hairless mouse skin and other organs after systemic and topical methotrexate treatment

DNA synthesis in epidermis, spleen, small intestine, and muscle of the hairless mouse was measured after systemic and topical methotrexate dosing. Mice intraperitoneally injected with methotrexate (5 mg/Kg) incorporated 3H-UdR in epidermis at 90% of baseline at 3 hrs, and the incorporation was not suppressed at 24 hrs. Muscle DNA synthesis was not suppressed. In the spleen and small intestine, incorporation was greatly suppressed to 10% at 3 hrs. On the other hand, after topically applied methotrexate (25 mg/Kg) treatment, epidermis and muscle were 60-90% of baseline at 3-24 hrs and spleen and small intestine were 5-10% at 3-6 hrs. In a prolonged time schedule study (4 days), epidermal incorporation after intraperitoneally applied methotrexate (5 mg/Kg) showed no suppression, but was instead stimulated to 180% at 2 days. 5-Fluorouracil, a thymidine kinase inhibitor in antitumor agents, was topically applied (25 mg/Kg) and compared for DNA synthesis. The incorporation of 3H-UdR was drastically suppressed at 3 hrs. The results suggest that methotrexate is percutaneously absorbed, but does not extensively suppress epidermal DNA synthesis in hairless mice, although it does suppress spleen and intestinal DNA synthesis.

The effect of aging on percutaneous absorption in man

Despite much research into the mechanisms of cutaneous aging and the identification of significant age-associated biological and biophysical changes within the skin, the question "How does aging affect percutaneous absorption (PA) in vivo?" remains unanswered. We have made in vivo measurements of PA in young (18-40 years) and old (greater than 65 years) subjects. Standard radiotracer methodology was employed and PA was quantified from the urinary excretion profiles of 14C radiolabel (corrected for incomplete renal elimination). Testosterone (TST), estradiol (EST), hydrocortisone (HC), benzoic acid (BA), acetylsalicylic acid (ASA), and caffeine (CAFF) have been studied. Permeation of HC, BA, ASA, and CAFF was significantly (p less than 0.01, 0.01, 0.01, and 0.05, respectively) lower in aged subjects, whereas the absorption of TST and EST was similar in the two groups. Thus it appears that aging can affect PA in vivo and that relatively hydrophilic compounds are particularly sensitive. The diminished surface lipid content of "old" skin implies a diminished dissolution medium for compounds administered topically. It is reasonable to speculate that this physiologic change will impact most severely upon those permeants whose lipid solubility is lowest (that is, HC, BA, ASA, CAFF). Furthermore, the typically reduced hydration of aged stratum corneum will compound this effect for these chemicals. Conversely, highly lipid-soluble chemicals (TST and EST) may still be able to dissolve readily into the stratum corneum even when the available lipid medium is reduced.

Post-application occlusion substantially increases the irritant response of the skin to repeated short-term sodium lauryl sulfate (SLS) exposure

Occlusion often, but not always, enhances percutaneous absorption and thus may facilitate skin irritation. Quantitative data about the impact occlusivity may have on minimal irritant stimuli to which the skin is exposed in daily life, and which may lead to chronic irritant contact dermatitis, are however lacking. Irritant stimuli were administered by repeated application of sodium lauryl sulfate (SLS) in an open application procedure. After the open exposure, the skin was either left open or occluded with plastic. Skin irritancy was assessed by means of visual grading and by transepidermal water loss (TEWL) measurements. Post-exposure occlusive treatment markedly enhanced the irritant response. 5 consecutive daily applications produced more irritation, with or without occlusion, than alternate day application. Occlusion may be a relevant factor in the development of irritant contact dermatitis from certain chemicals.