Introduction
Complexion coloration in different ethnic groups varies dramatically from dark to light, as exemplified by the skin of central African and northern Scandinavian individuals, respectively, despite the fact that the density of melanocytes in the skin of these two extreme skin types is identical.[1,2] The biological basis of human skin colour variation has been studied by numerous investigators over the years. The intrinsic complexion coloration is determined by the amount and type of melanin in the skin.[3] However, an equally important determinant of skin coloration is the variation in the quantity, packaging and distribution of epidermal melanin within keratinocytes of different ethnic groups.[4] It is well documented that the melanosomes within keratinocytes of dark skin are distributed individually in the cytosol, predominantly over the nucleus of the keratinocytes, whereas the melanosomes within keratinocytes of light skin are clustered together in membrane-limited groups of two to eight melanosomes, also in the cytosol predominantly over the nucleus. It is also known that there is a progressive variation in melanosome size with ethnicity, African skin having the largest melanosomes, European skin the smallest melanosomes, and the melanosomes in Indian, Mexican and Chinese skin being intermediate in size. However, most of these previous reports describe the distribution patterns of melanosomes among different ethnic groups in a subjective, qualitative nature. The extent to which the distribution patterns of melanosomes in the skin of different ethnic groups differ has never been defined precisely. Therefore, the aim of the current study was to use a quantitative approach to assess the distribution patterns of melanosomes that have been transferred to keratinocytes in skin from Asian individuals and to compare these data with those for light-skinned Caucasian and dark-skinned African/American individuals. We also measured the area of melanosomes with the intention of elaborating the quantitative difference between the size of individual and clustered melanosomes. The quantitative approach used in our study may potentially permit a new interpretation of the position of Asian skin in the model for global pigmentation.
