Undecylenic Acid

10-Undecenoic acid · Undecenoic acid

Snapshot

Indications	Contraindications
Tinea pedis^1–3 Fungal infections of the foot skin^{4, 5} Recurrent herpes labialis⁶	Pregnancy⁷ Nursing⁷

Undecylenic acid (10-undecenoic acid) is a fatty acid derived from castor oil⁸. It is used topically as an antifungal, chiefly for tinea pedis, and for recurrent herpes labialis. Oral capsules are taken by patients seeking yeast control, a use no trial has tested.

Human research is limited to about eight small trials, mostly in tinea pedis, with others in herpes labialis, infected dermatoses, and onychomycosis. In placebo-controlled trials, undecenoic acid was efficacious for fungal infections of the foot skin, and in one trial it performed comparably to tolnaftate in tinea pedis. A 1997 multicenter placebo-controlled trial found a topical cream reduced viral shedding in recurrent herpes labialis, with minimal clinical benefit outside the prodrome⁶. Products listing undecylenic acid come as capsules, softgels, and tablets, often in multi-ingredient formulas; see Form comparison.

For patients on medications, product labeling asks for a healthcare professional's advice before use⁷.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

30 sources, 17 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources