ABSTRACT
Human skin pigmentation is facilitated by melanocytes that synthesize the pigment melanin. The melanocytes reside in the basal layer of epidermis. Melanin is produced by specialized organelles within the melanocytes, called melanosomes. In healthy skin, melanocytes are distributed in a characteristic regularly dispersed pattern. Sun tanning results from a UV-induced increase in the production and release of melanin to the neighbouring keratinocytes, as well as a redistribution of melanin among these cells. The regulatory mechanisms of pigmentation and the tanning
response encompass cell self-organization, UV-sensing, auto-and paracrine signalling, melanocyte dendrite formation, as well as melanogenesis and melanosome transfer.In this chapter, we give a detailed presentation of the biological process of the skin pigmentation. Further, we review the mathematical models that have been deployed up until now in the field. We also present one of our own models more deeply. This is an ODE model describing the distribution of melanin in the layers of epidermis in response to UV irradiation. 3.1 BackgroundAround 1 million years ago, a tanningresponse evolved in our hominid ancestors in which the accumulationof melanin granules in skin cells provided physical protectionagainst the DNA-damaging effects of sunlight [1]. Today, the tanning response is exploited by millions of people each year for cosmetic reasons. Because of the increased risks for melanoma and squamous cell carcinoma following overexposure to sunlight [2], the molecular biology of the tanning response has been given substantial biomedical attention over the last decades from dermatologists and oncologists (reviewed by [3-7]), as well as from those seeking ways to achieve tanning independent of sunlight [8].
