Quaternium-15
1-(3-Chloroallyl)-3,5,7-Triaza-1-Azoniaadamantane Chloride
What it is
An antimicrobial preservative (CAS 4080-31-3 / 51229-78-8) that slowly releases formaldehyde in water-containing formulas to inhibit microbial growth.
In this product: Formaldehyde-releasing antimicrobial preservative.
Dose & route, what actually matters
Eye-area leave-on (mascara). Formaldehyde released from Quaternium-15 is in direct contact with conjunctival mucosa and periorbital skin, a high-sensitivity anatomical site with greater permeability than body skin.
EUROPEAN UNION
Permitted at maximum 0.2% (as free formaldehyde); mandatory 'contains formaldehyde' warning label if concentration exceeds 0.05% free formaldehyde. Directly in the EU's formaldehyde-releaser labeling regime.
UNITED STATES
No national ban as of 2026. Washington State Toxic-Free Cosmetics Act (TFCA, 2023) banned formaldehyde releasers effective January 1, 2025. US federal proposed rule (G/TBT/N/USA/2187, February 2025) would ban it nationally effective January 1, 2027. No mandatory warning label required nationally.
The evidence
Formaldehyde is classified as IARC Group 1 (carcinogenic to humans) based on nasopharyngeal cancer evidence in occupationally exposed workers (IARC Monograph Vol. 100F, 2012).
regulatory · 2012 · source
US proposed federal rule G/TBT/N/USA/2187 (Feb 2025) would ban cosmetics containing formaldehyde and formaldehyde releasers including Quaternium-15 nationally effective January 1, 2027. Washington State TFCA banned them effective January 1, 2025.
regulatory · 2025 · source
California Prop 65: Formaldehyde, the substance released by Quaternium-15, is listed on California Prop 65 as a known carcinogen.
How to avoid it
Look for mascaras labeled 'formaldehyde-free' and check the INCI list for Quaternium-15, DMDM Hydantoin, Diazolidinyl Urea, Imidazolidinyl Urea, and Bronopol, all formaldehyde releasers.
Where it hides
Editorial analysis of publicly available regulatory and peer-reviewed sources. Not medical advice. We name our evidence and link it, including when an ingredient is fine.