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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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Sweat glands: Black skin showed more mixed apocrine-eccrine sweat glands and more blood and lymphatic vessels than white skin.
Stratum lucidum: Finally, Montagna and Carlisle2 also observed the stratum lucidum, the layer beneath the stratum corneum composed of 3–5 layers of keratinocytes, and found the stratum lucidum in black skin was unaltered by UV exposure, whereas white skin was usually distorted by UV exposure.
Melanosome size and distribution: Szabo et al.3 observed that overall, the most striking difference between black and white skin appears to be the size of melanosomes and their distribution pattern. When comparing the epidermis of black skin to white skin, black skin demonstrated more and larger singly distributed melanosomes in corneocytes and keratinocytes. In darkly pigmented skin, large melanosomes are surrounded by a membrane, whereas in lighter skin, smaller melanosomes are clustered together in a single membrane.3
Additionally, Toda et al. found that melanosomal packaging is closer to the basal layer in more darkly pigmented skin, compared with Caucasian skin.4 Regarding variations in human skin color, Szabo noted the density of pigment producing melanocytes in the skin, approximately 1,000/mm2, was not found to vary with ethnicity.5 Conversely, the ratio between eumelanin and pheomelanin synthesis was demonstrated by Thody to be higher in black skin than white skin.6
Thong et al. examined the patterns of melanosome distribution in keratinocytes in Asian skin, and compared these to light Caucasian skin and dark African-American skin.7 In this study, the distribution pattern of melanosomes transferred to keratinocytes in photoprotected skin (volar forearm) from normal Asian individuals was examined. Results demonstrated that melanosomes in the keratinocytes of Asian skin were distributed both as individual and clustered melanosomes; 62.6% as individual and 37.4% as clustered.