Undecylenic Acid: What It Is and Why It's Used (flagship)

Origin

Undecylenic acid is an unsaturated fatty acid derived from castor oil — specifically from the pyrolysis of ricinoleic acid, the main fatty acid in castor oil. Its antifungal properties were identified in the 1940s, and it was approved by the FDA as an OTC antifungal active for tinea pedis (athlete's foot) and related superficial fungal infections. It entered personal care formulations — particularly foot care products and nail treatments — on this basis.

Why It's Used

It functions as an antifungal by disrupting the cell membrane and metabolic processes of susceptible fungi. In the United States, products containing undecylenic acid and its salts for antifungal claims are regulated as OTC drugs with mandated concentrations and required label language — they are not cosmetics. Products that do not make antifungal claims but contain undecylenic acid as an ingredient may be regulated differently.

Elsewhere

Undecylenic acid has industrial applications in the production of nylon-11, synthetic musks for fragrances, and various specialty chemicals. It is also used as a pharmaceutical starting material.

What the Framework Sees

Question Zero, and a scope-of-approval lesson for a third time in this series.

Get the full analysis in Volume Five →