Immediate pigment darkening: description, kinetic and biological function.

Immediate pigment darkening (IPD) is a transitory darkening of the skin observed after UVA exposure. The melanocytic system is implicated in its development. Indeed, it involves structural changes in melanocytes and keratinocytes and a chemical modification of pre-existing melanin. Darkening intensity is maximum immediately after exposure and decreases rapidly. The maximum efficiency wavelength for induction of IPD is around 340 nm. The phenomenon is inhibited by oxygen deprivation. Dose-response curves are linear for doses above 4 J/cm2. Minimum dose for induction of IPD (MIPDD) varies with the subject according to phototype, melanotype and skin color. The best criterion for predicting MIPDD seems to be chromametrically determined skin color. The biological role of IPD remains poorly understood; several hypotheses are discussed.