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Objective measurements of human skin colour were made with a tristimulus (L*a*b*) chromameter in a range of different ethnic skin types. These were compared with biochemical measurements of melanin content, melanin composition and melanosome size in skin biopsies obtained from the same sites. L*, a* and b* values were found to vary significantly with ethnicity. In general, constitutively dark skin types have lower L* values, higher a* values and higher b* values than constitutively light skin types. Total epidermal melanin content appears to be the primary determinant of L* values in human skin (r = -0.88; P < 0.00001), whilst melanosome size also has a significant but more subtle influence on L* values (r = -0.73; P < 0.00001). There is also a strong positive contribution to a* values from epidermal melanin (r = 0.66, P < 0.00001), which accounts for the ethnic variation in a* values observed in this study. Melanin is also a major contributor to b* values in lighter skin types (r = 0.71, P < 0.00001). However, this relationship breaks down in darker skin types where b* values actually reach a maximum and then decrease as the concentration of melanin in the skin increases. This appears to be because of optical masking of yellow light by high concentrations of melanin in the epidermis. Analysis of the relationships between L*, a* and b* values in human skin indicate that they are very closely interrelated, and suggest that the optical properties of melanin in the epidermis are very similar to those of a dye on a fabric substrate.

We have examined the quantity and composition of melanin in both photoprotected (volar upper arm) and chronically photoexposed (dorsal forearm) skin from a range of different ethnic skin types including African, Indian, Mexican, Chinese and European. The most lightly pigmented (European, Chinese and Mexican) skin types have approximately half as much epidermal melanin as the most darkly pigmented (African and Indian) skin types. However, the composition of melanin in these lighter skin types is comparatively more enriched with lightly coloured, alkali-soluble melanin components (up to three-fold). Regardless of ethnicity, epidermal melanin content is significantly greater in chronically photoexposed skin than it is in corresponding photoprotected skin (up to two-fold). However, by comparison there is only a modest enrichment of lightly coloured, alkali soluble melanin components in photoprotected skin (up to 1.3-fold). Analysis of melanosomes extracted from the epidermis in these subjects indicates that the proportion of spheroidal melanosomes is low in all skin types examined (<10%). This suggests that in human skin, pheomelanin is a very minor component of epidermal melanin, even in the lightest (European) skin types. Analysis of melanosome size revealed a significant and progressive variation in size with ethnicity: African skin having the largest melanosomes followed in turn by Indian, Mexican, Chinese and European. On the basis of these findings, we propose that variation in skin pigmentation is strongly influenced by both the amount and the composition (or colour) of the melanin in the epidermis. Variation in melanosome size may also play a significant role. However, the data also suggest that in human skin there are subtle differences in the mechanisms associated with the maintenance of constitutive pigmentation and facultative hyperpigmentation, respectively.

Explores the effect of chronic photoexposure on epidermal melanin content and composition in highly pigmented human skin in vivo. Techniques applied in the analysis of melanin content and composition in highly pigmented skin; Description of melanin; Analysis of melanosome morphology; Information on the determinant of human skin color and melanin production in normal human melanocytes.