The validity and practicality of sun-reactive skin types I through VI

The concept of sun-reactive "skin typing" was created in 1975¹for a specific need: to be able to classify persons<i>with white skin</i>in order to select the correct initial doses of ultraviolet A (UVA) (in joules per cubic centimeter) in the application of the then newly developed technique for the treatment of psoriasis—oral methoxsalen photochemotherapy (PUVA).²The need arose as a result of experience with several patients who were a "dark" phenotype (brown or even black hair, and some with brown eyes) but, to our surprise, developed severe phototoxic reactions following oral ingestion of 0.6 mg/kg of methoxsalen and then, two hours later, were exposed to 4 to 6 J/cm². These initial doses were obviously too high, and it was then understood that the estimation of the white-skinned person's tolerance level to oral PUVA could not be based solely on the phenotype (hair and eye color).