Skin phototoxicity variations during repeated bath PUVA exposures to 8-methoxypsoralen and trimethylpsoralen

When applying psoralens topically to the skin by a 15-min bathing procedure, a dilute trioxsalen solution (0.2 mg/l) produced a ten- to fifteen-fold stronger skin photosensitization than a two-fold more concentrated methoxsalen solution. There were both inter- and intra-individual variations in psoralen-induced photosensitivity when the treatments were repeated five times in each of five test subjects. In particular, the skin UV-A sensitivity increased progressively at each subsequent psoralen bathing, but this did not seem to be due to an accumulation of the psoralen in the skin.