Phenylmethylsulfonyl Fluoride

Phenylmethylsulfonyl fluoride (PMSF) is a synthetic protease inhibitor—a compound that blocks the activity of enzymes called proteases. In skincare formulations, it serves a preservative and stabilising function rather than a direct active ingredient. Its primary role is to prevent the degradation of other beneficial ingredients, particularly peptides and protein-derived compounds, which would otherwise break down when exposed to skin enzymes.

This ingredient is particularly useful in formulations containing peptide complexes or bioactive extracts sourced from organisms like amphibians, which naturally produce peptides alongside proteases. By inhibiting protease activity, PMSF helps maintain the integrity and efficacy of these sensitive actives over time and during skin penetration.

Proteases are enzymes naturally present in skin that break down proteins and peptides as part of normal skin metabolism. When peptide-rich ingredients are applied topically, these skin enzymes can degrade them before they have a chance to exert their intended benefits. PMSF works by inhibiting these proteases, essentially slowing or preventing this degradation process.

The mechanism is chemical: PMSF binds to and inactivates specific types of proteases (serine proteases), creating a protective environment for peptides and other protein-derived actives. This allows these ingredients to remain stable both in the product and during their interaction with skin.

PMSF is used as a functional ingredient in formulations—you won't typically see it featured as a star active. It works best in products specifically formulated with peptides or enzyme-sensitive botanical extracts. Look for it in serums, essences, or targeted treatments rather than basic moisturisers, and use these products as directed by the manufacturer.