The immunologic dysfunctions that are a major predisposing factor in psoriasis are believed to be the same in all persons regardless of skin color. The patterns of genetic inheritability for the predisposing factors may vary in different groups.
The pigmentation of skin is controlled by hormonal processes that are unrelated to the immune and inflammatory processes that underlie psoriasis. It is interesting to note that all humans, regardless of skin color, have about the same number of melanocytes (pigment-containing cells) at any given site on the skin. Variations in skin color are due to differences in hormonal regulation of pigment formation within the melanocytes, and transfer of the pigment from melanocytes to keratinocytes (the cells that make up the majority of the outer layer of skin). A principal hormone in the regulation of human skin color is melanocyte-stimulating hormone (MSH).
The incidence of psoriasis is much lower in dark-skinned West Africans and African-Americans than in light-skinned people of European ancestry. Incidence is also low in Japanese and Eskimos, and is extremely low to non-existent in Native Americans in both North and
The treatment of psoriasis in African-Americans is largely the same as treatment in light-skinned patients. An adjustment is therapy is made in the use of photochemotherapy (PUVA) and phototherapy. In PUVA, both the chemical photosensitizer and the ultraviolet dose are adjusted for skin type and pigmentation.