Skin whitening effect of linoleic acid is enhanced by liposomal formulations

Linoleic acid (LA) is known to have a whitening effect on hyperpigmented skin, and is encapsulated in liposomes for topical application because of its low solubility in aqueous solution, although the effect of liposomalization of LA on the whitening activity has not been evaluated. In the present study, we evaluated the effect of liposomalization on the whitening activity of LA by using LA in ethanol, hydrogel containing LA, and hydrogel containing liposomal LA towards the UV-stimulated hyperpigmented dorsal skin of brownish guinea pigs. The whitening effect was far greater for hydrogel containing liposomal LA (0.1% w/w as a final concentration of LA) than for free LA in ethanol or hydrogel containing LA. Next, the whitening effect of LA was examined with UV-stimulated hyperpigmented human upper arm skin by using a hydrogel containing liposomal LA (0.1% LA) and non-liposomal LA (3.0, 10.0% LA). Liposomal LA (0.1%) showed a whitening effect comparable to 10.0% non-liposomal LA and was far more effective than 3.0% non-liposomal LA. These results indicate that liposomal formulations are favorable for the transdermal application of LA.

Tacrolimus ointment promotes repigmentation of vitiligo in children: A review of 57 cases

BACKGROUND

Vitiligo is an autoimmune disorder characterized by loss of pigmentation. Phototherapy and application of topical corticosteroids are most commonly prescribed. However, these therapies are often not effective and use of corticosteroids on the face may lead to cutaneous atrophy, telangiectasia, and ocular complications.

OBJECTIVE

We sought to assess the efficacy of topical tacrolimus ointment in the treatment of pediatric vitiligo.

METHODS

A retrospective review was performed of 57 pediatric patients with vitiligo at two clinical sites. Patients were treated with tacrolimus ointment for at least 3 months. Clinical responses were documented during clinic visits, and by pretacrolimus and posttacrolimus photography.

RESULTS

At least partial response was noted to tacrolimus ointment on the head and neck in 89%, and on the trunk and extremities in 63% of patients. Facial vitiligo of the segmental type showed the best response rate. Two patients initially experienced burning on application.

CONCLUSIONS

Topical tacrolimus ointment is an effective alternative therapy for childhood vitiligo, particularly involving the head and neck.

Topical tacrolimus for treatment of childhood vitiligo in Asians

Childhood vitiligo is a common disorder of pigmentation in India. Considering the lack of uniformly effective and safe treatment modalities for children with vitiligo, search for newer therapeutic agents continues. This study was designed to evaluate the role of topical tacrolimus in the treatment of childhood vitiligo. Twenty-five children with vitiligo were treated with topical 0.03% tacrolimus ointment applied twice daily for 12 weeks. Response was noted as marked to complete (> 75% repigmentation), moderate (50-75% repigmentation) and mild (< 50% repigmentation). Twenty-two children (9 boys and 13 girls) of mean age 7.2 +/- 1.4 years completed the study. Twelve (54.5%) children had vitiligo vulgaris, nine (40.9%) had focal vitiligo and one (4.5%) had segmental vitiligo. The mean duration of disease was 8 +/- 3 months. Nineteen (86.4%) children showed some repigmentation at the end of 3 months and other three had no response. Of these 19 children, repigmentation was marked to complete in 11 (57.9%), moderate in five (26.3%) and mild in three (15.7%) children. Side effects were minimal, such as the pruritus and burning noted in only three patients. Topical tacrolimus is an effective and well-tolerated treatment modality in Asian children with vitiligo.

The Combined Effects of Extracts Containing Carotenoids and Vitamins E and C on Growth and Pigmentation of Cultured Human Melanocytes

In the present study, we investigated the effects of tomato extract (TE) containing lycopene and palm fruit extract (PE) rich in carotenoids on the growth and pigmentation of melanocyte cultures of Caucasian origin. The extracts were tested at different concentrations and in combination with vitamins E and C. Melanocytes with basic and increased (tyrosine-induced) pigmentation were treated in short-term and long-term experiments. Prevention of UVA-induced DNA damage was studied by using the comet assay. Melanocytes with stimulated melanin production showed reduced growth. Incubation of the cells with TE/PE (20/4 microg/ml) in combination with 35 microM vitamin E and 100 microM vitamin C (COMB 20/4) reduced this growth inhibition, especially in the long-term cultures. Increased production of melanin pigment was obtained when the cells were treated with 2.5 x and 10 x higher concentrations of the TE/PE and the same concentration of vitamins E and C (COMB 50/10 and 200/40). Reduced DNA damage was found after UVA irradiation in cells preincubated with COMB 50/10. The results indicate that the presence of carotenoids from TE and PE in combination with vitamins E and C may influence growth and pigmentation in melanocyte monocultures. Depending on the concentration of the carotenoid mixtures, their presence may provide some protection against the melanogenic intermediates and/or exogenous DNA damage.

[Diagnostic image (207). A woman with orange hands]

A 45-year-old woman was diagnosed with carotenaemia due to excessive intake of beta-carotene in a vitamin drink.

[Suicidal monointoxication with flunitrazepam. Further comment on coloration phenomena of the upper gastrointestinal tract]

Fatal monointoxications with benzodiazepines, for instance with a suicidal intention, are exceptional findings. We report the autopsy case of an 82-year-old woman who died due to a suicidal monointoxication with Rohypnol 1 mg film tablets (therapeutical agent: flunitrazepam). 0.065 mg/L flunitrazepam and 0.34 mg/L 7-aminoflunitrazepam were detected in a postmortem heart blood sample and toxicological analysis revealed the metabolite 7-aminoflunitrazepam in gastric contents, too. At external examination, a bluish-turquoise coloration was seen around the woman's right nostril and within the oral cavity. At autopsy, similar coloration phenomena were seen on the mucosa of the distal esophagus and the stomach. Formerly, bluish stains on mouth and nostrils were considered indicative of intoxications with organophosphates such as parathion (E 605). More recently, case reports accumulate where an intoxication with Rohypnol 1 film tablets (containing the coloring agent indigocarmine in its core) have to be considered as a potential differential diagnosis of such coloration phenomena.

Effects of a Superpotent Melanotropic Peptide in Combination With Solar UV Radiation on Tanning of the Skin in Human Volunteers

OBJECTIVE

Three phase 1 clinical trials of a superpotent melanotropic peptide, melanotan-1 (MT-1, or [Nle(4)-D-Phe(7)]alpha-melanocyte-stimulating hormone) were performed to demonstrate safety for MT-1 therapy combined with UV-B light or sunlight.

DESIGN

Open-label studies at 2 dose levels of MT-1 combined with small doses of UV-B to the neck or buttock or full sunlight to half of the back.

SETTING

Dermatology clinics at the Arizona Health Sciences Center, Tucson.

INTERVENTIONS

The first study randomized 4 subjects to MT-1 (0.08 mg/kg per day subcutaneously) and 4 subjects to injections of isotonic sodium chloride (9%) solution for 10 days, followed by neck irradiation with 3 times the minimal erythema dose (MED) of UV-B light. In the next study (n = 12), the MT-1 dosage was increased to 0.16 mg/kg per day for 10 days, with UV-B radiation (0.25-0.75 MED) given to a buttock site for 5 days during (n = 7) or after (n = 5) MT-1 administration. A final study randomized 8 subjects to 3 to 5 days of sunlight to half of the back or to sunlight plus 0.16 mg/kg of MT-1 for 5 days per week for 4 weeks.

RESULTS

Tanning in the first study was achieved in 3 of 4 subjects receiving MT-1, and these subjects also had 47% fewer sunburn cells at the irradiated neck site. More skin sites darkened with the higher dose of MT-1 in the second study. In the third study, there was significantly enhanced tanning of the back in the MT-1 group, and this was maintained at least 3 weeks longer than the tanning in the sunlight-only controls, who required 50% more sun-exposure time for equivalent tanning.

MAIN OUTCOME MEASURE

There were no pathologic findings at any UV-B or sun-exposed sites in any subject. Toxic effects due to MT-1 were minor, consisting of nausea and transient facial flushing.

CONCLUSION

Melanotan-1 can be safely combined with UV-B light or sunlight and appears to act synergistically in the tanning response to light.

Nutritional factors and susceptibility to arsenic-caused skin lesions in West Bengal, India

There has been widespread speculation about whether nutritional deficiencies increase the susceptibility to arsenic health effects. This is the first study to investigate whether dietary micronutrient and macronutrient intake modulates the well-established human risk of arsenic-induced skin lesions, including alterations in skin pigmentation and keratoses. The study was conducted in West Bengal, India, which along with Bangladesh constitutes the largest population in the world exposed to arsenic from drinking water. In this case-control study design, cases were patients with arsenic-induced skin lesions and had < 500 microg/L arsenic in their drinking water. For each case, an age- and sex-matched control was selected from participants of a 1995-1996 cross-sectional survey, whose drinking water at that time also contained < 500 microg/L arsenic. Nutritional assessment was based on a 24-hr recall for major dietary constituents and a 1-week recall for less common constituents. Modest increases in risk were related to being in the lowest quintiles of intake of animal protein [odds ratio (OR) = 1.94; 95% confidence interval (CI), 1.05-3.59], calcium (OR = 1.89; 95% CI, 1.04-3.43), fiber (OR = 2.20; 95% CI, 1.15-4.21), and folate (OR = 1.67; 95% CI, 0.87-3.2). Conditional logistic regression suggested that the strongest associations were with low calcium, low animal protein, low folate, and low fiber intake. Nutrient intake was not related to arsenic exposure. We conclude that low intake of calcium, animal protein, folate, and fiber may increase susceptibility to arsenic-caused skin lesions. However, in light of the small magnitude of increased risks related to these dietary deficiencies, prevention should focus on reducing exposure to arsenic.

Depigmentation ? a rare side effect to intra-articular glucocorticoid treatment

Intra-articular glucocorticoid injections are often used in patients with rheumatoid arthritis, either as bridging therapy or in periods with increased disease activity. We present a case of local skin depigmentation that occurred at the site of injection in a dark-skinned patient. Depigmentation is a rare complication of such therapy but may have important implications for dark-skinned patients.

Expression and function of peroxisome proliferator-activated receptors in human melanocytes

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) belong to the superfamily of nuclear receptors that heterodimerize with the retinoic X receptor. Agonists of PPAR have been known to play an important role in cellular responses including proliferation and differentiation. The expression and function of PPARs have not been investigated in human melanocytes, although they have been widely demonstrated in keratinocytes of the skin.

OBJECTIVES

To investigate the expression of PPARs in human melanocytes and the effects of PPAR activators on melanocyte growth and melanogenesis.

METHODS

We used immunocytochemistry and Western blot analysis to determine whether PPARs are expressed in melanocytes. To investigate further expression of PPAR subtypes, reverse transcriptase-polymerase chain reaction analysis was performed using PPAR subtype-specific oligonucleotides. The cell proliferation was measured using the Coulter counter. The effects on pigmentation were investigated with measurement of melanin contents, tyrosinase activity and its expression.

RESULTS

The mRNA of all three PPAR subtypes, PPAR-alpha, PPAR-beta/delta and PPAR-gamma, were expressed in melanocytes. Activators for PPAR-alpha (WY-14643) and PPAR-gamma (ciglitazone) inhibited proliferation of melanocytes in a dose-dependent manner, whereas bezafibrate, a preferential activator for PPAR-beta/delta, had no effect. This growth inhibition was accompanied by the morphological change of the melanocytes to an activated form with an increased number of dendrites and enlarged cell area compared with the control. The WY-14643 and ciglitazone also appeared to stimulate the melanin synthesis of melanocytes. This increase in pigmentation was due to stimulation of the tyrosinase activity without an increase in the expression of tyrosinase.

CONCLUSIONS

PPARs are expressed in human melanocytes and PPAR-alpha and PPAR-gamma activators inhibit melanocyte growth and stimulate melanogenesis.

Livide Verf�rbung der Hand als unerw�nschtes Ereignis bei axill�rer Plexusan�sthesie

During axillary brachial plexus block for hand surgery, the axillary artery was accidentally punctured. After skin disinfection of the operation site a livid discoloration of the hand appeared. The initial intention of stopping surgery and performing an angiography for clarification of the suspicion of a vessel lesion was dismissed after recording the pulse at the wrist and all fingertips employing a pulsoximeter. Further investigation showed that the livid discoloration of the hand was a product of the interaction of the octenidin solution used for pre-operative hand disinfection with the polyvidone-iodine solution used for surgical skin disinfection. This case report shows that interactions of topically administered pharmaceuticals have to be taken into consideration. Lack of knowledge might lead to unnecessary and unjustified diagnostic procedures which imply additional costs and dangers for the patient.

Depigmentation and Rejuvenation Effects of Kinetin on the Aged Skin of Hairless Descendants of Mexican Hairless Dogs

The depigmenting and anti-aging effects of kinetin (KN) solutions on the aged skin of hairless dogs were clinically and histologically investigated. Grossly, all KN-treated sites became mildly depigmented. At 50 days of topical treatment with KN solutions, apparent improvement was observed in the skin texture, wrinkling, and pigmentation. At 100 days of KN treatment, both the skin rejuvenation and depigmentation effects became more prominent. Throughout the experimental period of KN treatment, no adverse effects were found in any sites treated with KN solutions. In the colorimetric system, at 100 days of topical treatment with KN solutions, the L* and b* values in the sites treated with KN solutions significantly increased. Histologically, at 50 days of topical treatment with KN solutions, the KN-treated sites showed a decrease in the thickness of the corneal layers. Melanin granules decreased throughout all epidermal layers. In the dermis, the large number of fine collagen and elastic fibers were densely aligned. At the end of the treatment, this agent was equally effective against pigmented lesions irrespective of the concentration of KN solution. The distribution of melanin granules returned to normal in the skin of adult hairless dogs. Throughout the present study, there were no histologic abnormalities in the epidermis and the dermis. These results revealed that topical treatment with lower concentrations of KN solutions normalized hyperpigmentation and improved the aged skin structure of hairless dogs. In addition, it was clarified that KN solutions had no adverse effects on the skin of hairless dogs and that this agent was a safe chemical for long-term application.

Involvement of photooxidation of melanogenic precursors in prolonged pigmentation induced by ultraviolet A

Melanin is usually produced in melanocytes; however, our histologic research indicates that brownish black persistent pigmentation occurs at the basal layer and, partially, at the suprabasal layer of the epidermis, outside of melanocytes, in skin exposed to high doses of ultraviolet (UV) A radiation. This pigmentation remains for several weeks. We examined whether colorless melanogenic precursors participate in this UVA-induced persistent pigmentation. Among them, 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and its O-methyl metabolite, 6-hydroxy-5-methoxyindole-2-carboxylic acid (6H5MICA), can change into dark-colored pigment upon exposure to UVA, but not UVB, radiation, producing irreversible brownish black pigmentation. These hydroxyindole derivatives readily changed into dark-colored pigment upon UVA irradiation in the presence of hydrogen peroxide in vitro. Histochemical and biochemical studies demonstrated that 6H5MICA accumulates in excised skin specimens and supernatant of cultured human melanocytes. These results suggest that dark-colored pigment is generated directly, outside of melanocytes, in response to UVA exposure, by photooxidation of O-methyl metabolites of DHICA, such as 6H5MICA, at least. We propose that the pigmentation derived from this compound at the basal and suprabasal layers of the epidermis is involved in the mechanism of skin persistent pigmentation without reddening, observed after exposure to sunlight.

Deoxypodophyllotoxin reduces skin pigmentation of brown Guinea pigs

In this report, we have demonstrated that deoxypodophyllotoxin from Anthriscus sylvestris (L.) Hoffm decreases UV-induced skin pigmentation of brown guinea pigs. Deoxypodophyllotoxin (0.05 % in propylene glycol: ethanol: water = 5 : 3:2) was topically applied twice daily for two weeks to dorsal skin of brown guinea pigs that were exposed to UV irradiation using a solar simulator. Visual inspection and Fontana-Masson staining both demonstrated that deoxypodophyllotoxin reduced skin pigmentation and total epidermal melanin when compared to that of vehicle-treated areas, suggesting that deoxypodophyllotoxin maybe applicable to treat hyperpigmentation.

Focal Trichloroacetic Acid Peel Method for Benign Pigmented Lesions in Dark-Skinned Patients

BACKGROUND

Benign pigmented lesions, including seborrheic keratosis, solar lentigines, melasma, and freckles, are common disorders, and various treatment modalities have been tried. We suggest a technique consisting of focal trichloroacetic acid (TCA) peel applied by pressing firmly onto the focal lesions.

OBJECTIVE

To evaluate the clinical effects of focal TCA peel on pigmented lesions in dark-skinned patients.

METHODS

An analysis was conducted of 106 patients with benign pigmented lesions who were treated using focal TCA peel. Seborrheic keratosis was treated with 65% focal TCA peel, solar lentigines, and freckles with 50% to 65% focal TCA peel, and melasmas with 10% to 50% focal TCA peel. Patients had Fitzpatrick skin types IV-V.

RESULTS

Patient treatment data indicated that 19 of 23 (83%) patients with seborrheic keratosis, 42 of 49 (86%) patients with solar lentigines, 8 of 14 (58%) patients with freckles, and 11 of 20 (55%) patients with melasma experienced a good clinical response. Good satisfaction rates in the seborrheic keratosis, solar lentigines, freckles, and melasma groups were recorded. No significant complications were observed.

CONCLUSION

The focal TCA peel method presented in this study is a safe and effective modality for the treatment of benign pigmented lesions with no significant complications.

Cutaneous hypopigmentation following a posterior sub-tenon triamcinolone injection

PURPOSE

To report a case of cutaneous skin hypopigmentation following a posterior sub-Tenon triamcinolone acetonide injection for uveitis.

DESIGN

Observational case report.

METHODS

A 28-year-old African American female with Adamantiades-Behcet disease and panuveitis was administered a posterior sub-Tenon injection of triamcinolone acetonide and developed cutaneous hypopigmentation.

RESULTS

The patient developed skin hypopigmentation of the upper eyelid adjacent to the site of the sub-Tenon injection.

CONCLUSION

Injection of corticosteroids into the sub-Tenon space can cause hypopigmentation of the adjacent tissues, especially in heavily pigmented individuals.

Benzylamide derivative compound attenuates the ultraviolet B-induced hyperpigmentation in the brownish guinea pig skin

This study evaluated the effects of synthetic benzylamide compound I (2,6-dimethoxy-N-phenylbenzamide) on the ultraviolet B (UV B)-induced hyperpigmentation of the skin. UV B-induced hyperpigmentation was elicited on brownish guinea pig skin according to the method reported by Hideya et al. [Arch Dermatol Res 290 (1998) 375] with minor modifications. A lightening effect was observed following the topical application of compound I on UV-stimulated hyperpigmentation. The skin returned to its original color after treatment with compound I. Fontana-Masson staining indicated that melanin level in the hyperpigmented area was significantly decreased in the compound I-treated animals. However, the number of melanocytes were not changed in the compound I-treated groups using the S-100 stain, which is an immunohistochemical method. In vitro experiments using the cultured melanoma cells showed a 31.7% inhibition of melanin production by compound I at 100 microM. In addition, this compound had no effect on the tyrosinase enzyme function. However, it exhibited a catalyzing effect on the dopachrome transformation into 5,6-dihydroxyindole-2-carboxylic acid. Overall, the pigment-lightening effects of the compound I may due to the dopachrome tautomerase stimulation.

Evidence and utility of melanin degrading enzymes

The biochemical synthesis of human melanin is understood in some detail. However, little is known about melanin degradation and catabolism of melanin. We hypothesize that human skin contains enzymes that degrade melanin and these enzymes can be used to reduce skin color. To test this hypothesis, HaCaT keratinocytes and normal human keratinocytes in culture were pulse labeled for one hour with radiolabeled synthetic melanin. This melanin was synthesized in vitro using tyrosinase enzyme from mushrooms and using radiolabeled [14C]3,4-dihydroxyphenylalanine (DOPA) as a substrate. After the initial pulse labeling, samples of both the cells and media were taken at 2, 4, 6 and 18 hours. Over these time periods the counts remaining in the media and cell fraction were significantly decreased. This data suggests the need for new protein synthesis and the lysosome organelle function for the degradation. Melanin degrading extracts isolated from Aspergillus fumigatus and Saccharomyces cerevisiae were applied to human skin. These extracts cause significant reduction in UVB induced pigmentation. These extracts may be useful in developing new whitening products to even skin color and tone.

Topical Application of a Protein Kinase C Inhibitor Reduces Skin and Hair Pigmentation

To determine whether inhibition of PKC-beta activity decreases pigmentation, paired cultures of primary human melanocytes were first pretreated with bisindolylmaleimide (Bis), a selective PKC inhibitor, or vehicle alone for 30 min, and then treated with TPA for an additional 90 min to activate PKC in the presence of Bis. Bis blocked the expected induction of tyrosinase activity by activation of PKC. Addition of a peptide corresponding to amino acids 501-511 of tyrosinase containing its PKC-beta phosphorylation site, a presumptive PKC-beta pseudosubstrate, gave similar results. To determine whether Bis reduces pigmentation in vivo, the backs of four shaved and depilated pigmented guinea pigs were UV irradiated with a solar simulator for 2 wk excluding weekends. Compared to vehicle alone, Bis (300 microM), applied twice daily to paired sites for various periods encompassing the irradiation period, decreased tanning. Bis also, although less strikingly, reduced basal epidermal melanin when topically applied twice daily, 5 d per wk, for 3 wk to shaved and depilated unirradiated skin. Moreover, topical application of Bis (100 microM) once daily for 9 d to the freshly depilated backs of 8-wk-old mice markedly lightened the color of regrowing hair. These results demonstrate that inhibiting PKC activity in vivo selectively blocks tanning and reduces basal pigmentation in the epidermis and in anagen hair shafts.

A Comparative Study of Punch Grafting Followed by Topical Corticosteroid Versus Punch Grafting Followed by PUVA Therapy in Stable Vitiligo

BACKGROUND

Punch grafting followed by PUVA is an established therapy for stable vitiligo, but punch grafting followed by topical corticosteroid has never been evaluated.

OBJECTIVE

The aim of this study was to evaluate the efficacy of topical corticosteroid in perigraft pigmentation and to compare it with perigraft pigmentation after PUVA in patients with stable vitiligo.

METHODS

Fifty patients with stable vitiligo of various clinical types were subjected to punch grafting. In a randomized case study, these patients were divided into two groups: One group received post punch-grafting PUVA (group I) and the other group post punch-grafting topical application of fluocinolone acetonide 0.1% (group II). During the follow-up period of 6 months, six patients were lost to follow-up, and two patients were excluded from the study; 42 patients were evaluated for pigment spread and side effects.

RESULTS

In group I, the average pigment spread was 6.38 mm, whereas in group II, it was 6.94 mm, showing a slightly higher pigment spread in group II, which was statistically not significant (P=0.301). There was no difference in response to therapy in patients having segmental vitiligo as compared with nonsegmental vitiligo. Cobblestoning, depigmentation of the grafts, infection, and graft displacement were the important side effects seen in some patients in both the groups.

CONCLUSION

The study shows that the pigment spread with topical corticosteroid is comparable to that with PUVA. However, the studies with long-term follow-up are required to establish this. The advantages of topical corticosteroid are that its use is easy, less cumbersome, cheaper, and more cost effective than PUVA.

Sunless skin tanning with dihydroxyacetone delays broad-spectrum ultraviolet photocarcinogenesis in hairless mice

Sunless tanning with dihydroxyacetone (DHA) is not considered to be a sunscreen although it does absorb parts of the ultraviolet (UV) spectrum. We investigated the protection with topical application of DHA against solar UV-induced skin carcinogenesis in lightly pigmented hairless hr/hr C3H/Tif mice. Broad-spectrum UV radiation, simulating the UV part of the solar spectrum was obtained from one Philips TL12 and five Bellarium-S SA-1-12 tubes. Three groups of mice were UV-exposed four times a week to a dose-equivalent of four times the standard erythema dose (SED), without or with application of 5 or 20% DHA only twice a week. Similarly, three groups of mice were treated with DHA and irradiated with a high UV dose (8 SED), simulating a skin burn. Two groups (controls) were not irradiated, but either left untreated or treated with 20% DHA alone. The UV-induced skin pigmentation by melanogenesis could easily be distinguished from DHA-induced browning and was measured by a non-invasive, semi-quantitative method. Application of 20% DHA reduced by 63% the pigmentation produced by 4 SED, however, only by 28% the pigmentation produced by 8 SED. Furthermore, topical application of 20% DHA significantly delayed the time to appearance of the first tumor >or=1mm (P=0.0012) and the time to appearance of the third tumor (P=2 x 10(-6)) in mice irradiated with 4 SED. However, 20% DHA did not delay tumor development in mice irradiated with 8 SED. Application of 5% DHA did not influence pigmentation or photocarcinogenesis. In conclusion, this is the first study to show that the superficial skin coloring generated by frequent topical application of DHA in high concentrations may delay skin cancer development in hairless mice irradiated with moderate UV doses.