Singlet oxygen reacts with inhibitors of ultraviolet mediated damage to skin: p-aminobenzoic acid and its derivatives

P-Dimethylaminobenzoate, p-aminobenzoate, and ethyl-p-dimethylaminobenzoate react with singlet molecular oxygen, photochemically generated with hematoporphyrin as a sensitizer, to yield spectrally distinguishable products. The reaction is potentiated by D 2O and is competitively inhibited by methionine. p-Aminobenzoic acid and its derivatives are often used topically to prevent actinic damage to skin. They are thought to act solely as physical screens to absorb UV light. Their reactivity toward singlet oxygen, however, may also play an important role in the protective effect.