Ingredient Science

Undecylenic Acid, Explained

By the KeraFirm Research Desk · August 16, 2026 · 6 min read

In Short

Undecylenic Acid USP is a long-established topical compound, and the only ingredient in KeraFirm Pro's formula with a stated concentration: 5%.

Worth understanding both what it traditionally does and why a declared percentage matters more than it might seem.

What undecylenic acid is

Undecylenic acid is a fatty acid derived from castor oil, long used in topical formulas for its surface-level antifungal properties. Background is available on WebMD. It works by creating conditions on the treated surface that are less favourable for fungal buildup.

Why the declared percentage matters

The transparency point worth noting: most ingredients in this product category are named without a stated concentration. Undecylenic Acid USP at 5% is a specific, checkable figure — you can compare it directly against other topical products that also declare their active ingredient percentage, which most formulas in this space do not offer.

What 'USP' means

USP refers to United States Pharmacopeia standards, a quality benchmark for ingredient purity and identity. Seeing 'USP' after an ingredient name indicates the compound meets that pharmacopeial standard, which is a meaningful quality marker separate from the concentration figure itself.

What it does not do

Undecylenic acid is a cosmetic-grade topical ingredient in this formula, not an FDA-approved prescription antifungal drug. It is positioned to support the appearance of the treated area over time, not to guarantee elimination of an underlying infection.

Applying this to KeraFirm Pro

Undecylenic Acid USP is the backbone of KeraFirm Pro's nine-ingredient formula, working alongside eight conditioning oils and extracts that are named but not individually quantified.

About this article: written by the KeraFirm Research Desk for general information. It is not medical advice. This is an independent site and earns a commission on purchases through links to the official seller — see our editorial standards.