Absence of Psoralen—type Phototoxicity from Usnic Acid, Some Lichens, and Lichen Substances

Abstract

Usnic acid, one of about 90 “lichen substances” which are produced by lichenized fungi, has been reported to cause allergic contact dermatitis (1, 2). In view of a resemblance between the molecular structure of usnic acid (dibenzofuran) Fig. 1(a) and that of psoralen (furocoumaran) Fig. 1(d), which is a photosensitizer of human skin, usnic acid and some lichens and lichen substances were tested for phototoxic activity. The procedure used was that described by Daniels (3).