Phototoxicity to a sunscreen ingredient. Padimate A.

Para-aminobenzoic acid and certain of its esters are widely used in sunscreens. We found that one of these, amyl paradimethylaminobenzoate (padimate A) was capable of provoking phototoxic reactions; With ultraviolet A (UV-A) dosages of about 30 joules/sq cm, a reaction grossly resembling sunburn developed in most subjects. The dominant histological feature was vacuolar degeneration of the epidermis without sunburn cells. Proprietary sunscreens containing padimate A were also shown to produce a similar reaction. Our explanation for the paradox of a sunscreen that promotes "sunburn" is that, as affected users have concluded, the product was ineffective. The similarity between sunburn and a phototoxic response has delayed recognition of this adverse effect until now.