UROCANIC ACID ISOMERS IN HUMAN SKIN - ANALYSIS OF SITE VARIATION

Urocanic acid (UCA) is found in the stratum corneum as the trans-isome r and, on ultraviolet (UV) irradiation, photoisomerization into cis-UC A takes place. Cis-UCA has been suggested to play a part in UV-induced immunosuppression. In the present study, the concentration of UCA and the percentage as cis-UCA at 10 different body sites of 20 normal vol unteers were analysed. A large interindividual variation in total UCA concentration was found, but the mean UCA concentration in each site w as similar, other than at the sole of the foot. There was little varia tion in the UCA content between sites normally exposed, and not expose d, to light, but the percentage of UCA in the cis form was clearly hig her at exposed areas.