Melanin content and distribution in the surface corneocyte with skin phototypes

An individual's sensitivity to sunlight is traditionally assessed by the Boston or Fitzpatrick classification of skin type. The ability to tan depends, to some degree, on the melanin content of the epidermis. In the study reported here, surface corneocytes in exposed skin and unexposed skin have been assessed using a surface stripping slide mounting technique and an Optomax V image analyser, with which the percentage of corneocyte area occupied by melanin granules has been taken as the melanin content index (MCI). There was a significantly different MCI between different skin types for both exposed (P < 0.0001) and unexposed (P < 0.0001) areas using the Kruskal-Wallis one-way ANOVA test. There was also a positive significant correlation between MCI and skin types II-VI in both exposed (r = 0.95, P < 0.001) and unexposed areas (r = 0.89, P < 0.005). Image analysis also demonstrated that the number of melanin granules in surface corneocytes was significantly higher in the exposed area compared with the unexposed area, for skin types II, III, IV, V and VI. Melanin cap-like structures were also observed in exposed corneocytes and heavily pigmented skin contained larger melanin particles than fairer skin. The results indicate that an individual's skin phototype and melanin content, assessed by image analysis, have a significant correlation.