Phototoxicity and skin damage: A review of adverse effects of some furocoumarins found in natural extracts.

The phototoxicological effects of furocoumarins have been extensively studied. In association with UVA, some of these natural constituents of botanical isolates used in cosmetics, can be photoirritant, photogenotoxic and/or photocarcinogenic. Importantly, not all furocoumarins share the same degree of potency and some are inactive. The more potent furocoumarins, 8-methoxypsoralen and 5-methoxypsoralen, have been subject to extensive mechanistic studies. The formation of adducts with DNA has been widely studied but other contributary mechanisms have also been proposed. The phototoxicological effects, ranging from photoirritation to photocarcinogenicity, are dependent on the dermal dose of furocoumarin and the fluence (dose) of filtered, artificial UVA light. This is particularly evident from photocarcinogenicity studies in animals and from the effect of sequential irradiation sessions in patients receiving Psoralen-UVA (PUVA) therapy. A currently enforced limit of 1 ppm for sun bronzing and sunscreen products for which prolonged intentional exposure to UVA is likely, and 5ppm total furocoumarin concentration in other cosmetic products, e.g., facial cosmetics, that are likely to be only exposed to adventitious and intermittent UVA irradiation, provides a suitably protective threshold when compared to the UV exposure that has been used in studies on animals and in treating PUVA patients.