Further studies of photoaugmentation in humans: phototoxic reactions

The addition of modest amounts of long ultraviolet light (UV-A) to 1/2 minimal erythema dose (MED) of sunburning irradiation (UV-B) produced erythema visible at 24 hr, the prototype of the photoaugmentation phenomenon. The results were the same whether UV-A was given before or after UV-B. Photoaugmentation could be demonstrated after an inverval of 6 hr between doses, but not after 1 day. Photoaugmentation has also been demonstrated clinically and histologically with two topical photosensitizers, coal tar and 8-methoxy-psoralen.