Effects of water temperature on photosensitization in bath-PUVA therapy with 8-methoxypsoralen

The pharmacokinetic aspects of bath-PUVA are not completely clarified. Therefore, we determined the phototoxic response of human skin following psoralen baths at temperatures ranging from 32°C to 42°C (71.6–107.6°F) and UVA doses ranging from 0.5 to 5.5 J/cm². The highest therapeutical photosensitization (i.e., lowest minimal phototoxic dose) was assessed at temperatures of 37°C (98.6°F) and above. Photosensitization was significantly decreased at lower temperatures. These data indicate that a bath temperature of 37°C (98.6°F) should be used to gain optimal therapeutic efficiency in a clinical setting. Furthermore, in order to minimize the risk of adverse phototoxic effects in bath-PUVA, it is important to use a constant temperature during the psoralen bath.