Variations in Pigmentation and Ultrastructural Skin Differences Among Ethnic Groups

By: Rupa Pugashetti, MD, Santa Clara Valley Medical Center, and Howard I. Maibach, MD, University of California School of Medicine

Posted: September 1, 2010, from the September 2010 issue of Cosmetics & Toiletries.

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In dark skin keratinocytes, melanosomes were found to be predominantly individual (88.9%), whereas in light Caucasian skin keratinocytes, melanosomes were predominantly clustered (84.5%). Therefore, the melanosome distribution in Asian keratinocytes appeared to be an intermediate between light Caucasian and dark keratinocytes. In addition, the size of melanosomes appeared to vary with ethnicity; melanosomes in dark skin were the largest, followed by melanosomes of Asian and then Caucasian skin. Furthermore, melanosomes that were distributed individually tended to be larger than clustered, smaller melanosomes.

Keratinocyte regulation of melanosomes: Minwalla et al. examined in vitro the role keratinocytes play in regulating the distribution patterns of recipient melanosomes.⁸ Co-cultures of melanocytes and keratinocytes from different racial backgrounds were studied using electron microscopy. When keratinocytes from dark skin were co-cultured with melanocytes from either dark or light skin, the recipient melanosomes were found to be predominantly individual as opposed to clustered. However, when keratinocytes from light skin were co-cultured with melanocytes from dark or light skin, recipient melanosomes were predominantly clustered as opposed to individual. Therefore, recipient melanosomes are predominantly distributed in membrane-bound clusters from light skin keratinocytes and distributed individually by dark skin keratinocytes. Furthermore, melanosome size was not related to distribution. This work suggested that keratinocyte regulatory factors may determine how recipient melanosomes are distributed.

Epidermal melanin: Alaluf et al. examined the melanin content in photoexposed and photoprotected skin of various ethnic types including African, Indian, Mexican, Chinese and European.⁹ Lightly pigmented skin types—i.e., Mexican, Chinese and European—were found to have approximately half as much epidermal melanin as darkly pigmented skin types. Furthermore, the melanin composition among the lighter skin types was more enriched with lightly colored, alkali-soluble melanin pigments such as pheomelanin and eumelanin.

Epidermal melanin content was found to be greater in chronically photoexposed skin than photoprotected skin, regardless of ethnic background. This analysis, like previous studies, also demonstrated that melanosome size varies with ethnicity: African skin exhibited the largest melanosomes, followed by Indian, Mexican, Chinese and finally, European. Therefore, the amount and composition of melanin, and differences in melanosome size may all play roles in determining skin pigmentation.

Gluthathione: Halprin et al. reported that glutathione may play a role in the genetically determined differences in skin color among different races.¹⁰ This sulfydryl-containing epidermal compound plays a role in melanin formation. Halprin described that the tripeptide glutathione (γ-glutamyl-cysteinyl-glycine) is present in the human epidermis in sufficient concentrations to be the inhibitor of melanin formation from tyrosine by tyrosinase. Glutathione in its reduced state (GSH) as well as the enzyme glutathione reductase, which maintains GSH levels, were found in lower concentrations in African skin than in Caucasian skin.

Genetics of Skin Pigmentation