Effects of intensive application of retinoic acid on human skin.

The daily application of 0-3% retinoic acid to the back produced an acute irritant dermatitis which resolved to a near-normal clinical appearance within 40 days despite continued daily exposure. Hardened skin was markedly altered physiologically. The responses to DMSO, histamine and the histamine liberator, compound 48/80, were sharply enhanced. This reflected enhanced permeability resulting from reduction of the horny layer to less than one-half its normal thickness. Phototoxic and irritant substances produced exaggerated reactions owing to greater penetration. A paradoxical decrease in delayed sinsitivity to streptodornase-streptokinase was attributed to enhanced clearance of the antigen.