One hundred and five people with fungal toenail infection were randomly assigned to daily application of either 40% urea ointment under a plastic dressing, or a bifonazole-and-urea ointment, for up to three weeks. Both groups then used an antifungal cream for eight weeks. Assessors who did not know which treatment anyone had received judged whether the diseased nail plate had been fully removed at three weeks: 61% for the 40% urea group against 39% for the comparison. This is worth understanding correctly. Urea is not killing the fungus. It softens the keratin so the diseased nail can be lifted away without cutting, which then lets an antifungal reach what is underneath.
Lahfa M, Bulai-Livideanu C, Baran R, et al. Efficacy, safety and tolerability of an optimized avulsion technique with Onyster (40% urea ointment with plastic dressing) compared to bifonazole-urea ointment for removal of the clinically infected nail in toenail onychomycosis: a randomized evaluator-blinded controlled study. Dermatology. 2013;226(1):5-12.