One percent14C-hydrocortisone acetate in a cream vehicle with and without 10% urea was applied to the ventral forearm of five adult male volunteers in a crossover experiment. Using the urinary recovery of14C as an index of penetration, the addition of urea to the cream increased penetration approximately twofold.
Feldmann RJ, Maibach HI. Percutaneous Penetration of Hydrocortisone With Urea. Arch Dermatol. 1974;109(1):58-59. doi:10.1001/archderm.1974.01630010038008