Dehydroacetic Acid
Also known as Dehydroacetic acid, DHA, 3-Acetyl-6-methylpyran-2,4(3H)-dione, Methylacetopyranone
“EU CosIng says: restricted.”
Dehydroacetic acid (CAS 520-45-6) is a cyclic diketone preservative with fungicidal and bactericidal activity used in cosmetics at concentrations up to 0.6%. The CIR Expert Panel originally concluded it safe in 1985 (JACT 4(3):123-59) and reaffirmed that conclusion in 2003 and again in 2024 (Cherian et al., IJT 43(4 Suppl):130-134, PMID 38913451). A 2026 percutaneous absorption study confirmed limited skin penetration at permitted cosmetic concentrations (PMID 41666436). Toxicology studies using its sodium salt have identified potential anticoagulant effects via the mTOR/ERK pathway at systemic exposure levels (PMID 38103582), though these are not considered a concern at topical cosmetic use concentrations.
CIR Expert Panel has repeatedly concluded safe as used in cosmetic products (1985, 2003, 2024 re-reviews); no concentration cap imposed by CIR for leave-on or rinse-off applications
Effective antifungal preservative widely used in natural and conventional cosmetics at 0.1–0.6%; commonly paired with benzyl alcohol for broad-spectrum protection
Good stability across pH range typical for cosmetics; compatible with many formulation types including emulsions, shampoos, and leave-on creams
Permitted in organic/natural cosmetic certifications (COSMOS, ECOCERT) at permitted concentrations
- · EU Annex V explicitly prohibits use in aerosol dispensers (sprays) — inhalation risk is the implied rationale; products must not use this preservative in spray formats
- · Limited antibacterial efficacy compared to antifungal potency — works primarily against fungi and yeasts with weaker action against bacteria, often used in combination with other preservatives
Anticoagulant effect mechanism identified for sodium dehydroacetate at systemic exposure levels via mTOR/ERK pathway — not a concern at topical cosmetic concentrations but flagged in precautionary toxicology literature
Regulatory discrepancy: EU Annex V entry number cited as Entry 33 in some references and Entry 13 in others — the entry covers the same chemical family (3-acetyl-6-methylpyran-2,4(3H)-dione and salts)
CIR Quick Reference Table (12/2017, revised 07/2018) — Dehydroacetic Acid row: Finding=S, Citation=JACT 4(3):123-59, 1985 confirmed 11/03…
“Dehydroacetic Acid | S | | JACT 4(3):123-59, 1985 confirmed 11/03 IJT 25(S2), 2006”— QRT-122017revised072018.pdf, p. 42
Regulation (EC) No 1223/2009 Annex V — Entry 33: 3-Acetyl-6-methylpyran-2,4(3H)-dione and its salts; max 0.6% (as acid); not to be used i…
“Reference number 33: 3-Acetyl-6-methylpyran-2,4(3H)-dione and its salts -- 0,6 % (as acid); Not to be used in aerosol dispensers (sprays)”— Regulation (EC) No 1223/2009, Annex V, Entry 33