ABSTRACT
Melanocytes and melanins are largely responsible for the phototype-related color of the skin. The varied colors of skin depend on the nature, amount, size, and distribution of melanin pigment produced by melanocytes and transferred to keratinocytes. The system is governed by the epidermal melanin unit corresponding to a functional entity composed of one melanocyte and its neighboring keratinocytes into which the melanosomes are transferred. Chronic ultraviolet (UV) radiation provides a positive signal to the exposed epidermal melanin unit. In this instance, the number of active melanocytes increases, and individual melanocytes are stimulated to produce more melanins. In addition, melanosome transfer from melanocytes to the surrounding keratinocytes is enhanced through the intervention of the protease-activated receptor 2 (1).
