The potential hazards of repeated topical application of salicylic acid under occlusion to large areas of the body was evaluated by measuring the percutaneous absorption and serum salicylate concentrations in four patients with active psoriasis.
Serum salicylate concentrations never exceeded 5 mg/100 ml in any of the patients, and although greater than 60% of the salicylic acid applied was absorbed, no evidence of accumulation or toxicity was observed. This form of treatment appears to present little potential hazard even in patients with extensive skin disease. Therapy could be hazardous for patients with impaired hepatic or renal function or for smaller children.
The urinary excretory products of salicylate metabolism were compared following topical and intravenous salicylate administration to determine if the skin plays any part in the biotransformation of salicylate during percutaneous absorption. Our data are too limited and inconclusive to answer this question.
Taylor JR, Halprin KM. Percutaneous Absorption of Salicylic Acid. Arch Dermatol. 1975;111(6):740-743. doi:10.1001/archderm.1975.01630180068008