Dehydroacetic Acid

Dehydroacetic acid is a preservative typically used around 0.2–0.6% (often paired with benzyl alcohol) and is generally well tolerated but can sting or cause irritant reactions, especially on compromised barriers. Patch-test and real-world reports indicate occasional irritation and rare allergy, with risk increasing when combined with other potentially irritating preservatives or used on eczema-prone skin. For sensitive populations, I rate it as mild rather than gentle to reflect this non-zero, clinically observed reactivity. Safety Notes: Dehydroacetic acid is used as a preservative (often paired with benzyl alcohol or other co-preservatives) and in many emulsions/toners it appears at low levels around 0.01–0.05% as part of a broader preservative system. In the EU, dehydroacetic acid is permitted up to 0.6% (as acid) in cosmetic products, and a number of consumer-available “preservative-free/alternative preserved” formulas and concentrate-style products formulate close to this cap to ensure robustness, typically in leave-on products where preservation demands are higher; rinse-off products are more commonly toward the lower end.