Photoprotective effect of a psoralen-UVA-induced tan.

To determine whether a tan produced by 8-MOP and UVA protects from subsequent solar light irradiation, volunteers were irradiated with unfiltered Xenon arc light before and 10 days after a 1 week's course of four 8-MOP-UVA treatments. Evaluation of the minimal erythema doses and of histological changes before and after 8-MOP-UVA treatment revealed that the 8-MOP-UVA induced tan protected against the erythemogenic and cell damaging effects of Xenon arc light. Unscheduled repair DNA synthesis, used as a measure for UVB-induced DNA damage and repair, was also investigated in skin irradiated with the Xenon arc before and after 8-MOP-UVA induced tanning. Both the number of grains per sparse labeled cell and the number of sparse labeled cells per 1000 cells, were found to be significantly lower in tanned skin; taking decreased unschedules repair DNA synthesis as a measure for decreased DNA-damage, these findings also demonstrate a photoprotective effect of the 8--MOP-UVA induced tan.