Abstract
The most commonly observed hyperpigmen-tation is that caused by exposure to ultraviolet irradiation. The melanin pigment response is said to be of three types; melanin darkening, melanin migration and melanin formation (1). Melanin darkening appears within a few minutes after exposure to irradiations of relatively long wave length (3,000-4,200 A) with a maximally effective action spectrum of 3,400 A. This response is said to be oxygen-dependent as it is abo.ished if the skin is blanched by pressure applied with a quartz plate. Melanin migration is said to occur several days after exposure to an ultraviolet source and consists of an upward migration of melanin granules in the epidermis (Keller (2)). Melanin formation, according to the reflectance studies of Edwards and Duntley (3) begins after two days and reaches a maximum after nineteen days, and ceases after one month. The skin does not return to its initial melanin content until nine and a half months later.
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