Dehydroacetic Acid

Overview

Dehydroacetic acid (DHA) is a synthetic organic acid used as a broad-spectrum preservative in cosmetics. It comes as a fine white to off-white crystalline powder with a faint acidic odour. It is effective against bacteria, yeast, and mould — one of the few single preservative ingredients that covers all three classes of spoilage organisms.

The combination of dehydroacetic acid + benzyl alcohol has become one of the most widely used paraben-free preservation systems in the cosmetics industry. You will find this pairing in hundreds of commercial products, from luxury serums to drugstore moisturisers. The two complement each other well: benzyl alcohol acts as a solvent that helps dissolve the otherwise poorly soluble DHA, while DHA provides the heavy antimicrobial lifting. Many suppliers sell them pre-blended as a ready-to-use liquid.

There are two forms to know about. The acid form (dehydroacetic acid) is oil-soluble and goes into the oil phase. The sodium salt form (sodium dehydroacetate) is water-soluble and goes into the water phase. Both do the same job — the salt is simply the water-friendly version. Most hobbyist suppliers sell the pre-blended liquid (DHA + benzyl alcohol), which simplifies things considerably.

What it does in a formula

Primary role: broad-spectrum preservation. DHA inhibits the growth of gram-positive bacteria, gram-negative bacteria, yeast, and mould. It works by interfering with microbial enzyme systems, particularly those involved in energy metabolism.

It is notably effective against Aspergillus niger (a common mould contaminant) and Candida albicans (a common yeast), which are the organisms that many other preservatives struggle with.

When paired with benzyl alcohol, the system is synergistic — the combination is more effective than either ingredient alone at the same total concentration. Benzyl alcohol also serves as a co-solvent, improving DHA’s distribution throughout the formula.

How to use

Acid form (dehydroacetic acid): Use at 0.1-0.6%. It is oil-soluble — dissolve in the oil phase during heating. It needs warmth to dissolve fully; below about 50°C it tends to precipitate.

Sodium salt form (sodium dehydroacetate): Use at 0.1-0.5%. It is water-soluble — add to the water phase. Much easier to work with if you are making a water-heavy formula without much oil phase.

Pre-blended with benzyl alcohol: Follow the supplier’s recommended use rate, typically 0.5-1.2% of the total formula. Add at the cool-down phase (below 40°C). This is the easiest option for hobbyists.

pH matters: DHA works best between pH 3-6. Above pH 6, efficacy starts declining. Above pH 7, it is significantly weakened. Always check your finished pH.

Heat stability: DHA is reasonably heat-stable, but best practice is to add it at cool-down to preserve maximum activity.

Best for / Worst for

Best for: lotions, creams, serums, toners, shampoos, conditioners, body washes — essentially any water-containing formula at pH 6 or below. Particularly strong where mould and yeast are a concern (botanical-heavy formulas, hydrosol-based toners).

Worst for: formulas above pH 6.5 (efficacy drops sharply). Anhydrous products (no water, no preservation needed). Leave-on baby products in some jurisdictions (check local regulations). Formulas where you need a certified-natural preservative system — DHA is synthetic.

Common pitfalls

Ignoring pH. DHA is pH-dependent. A cream at pH 7 will not be adequately preserved by DHA alone, even at maximum use rate. Keep formulas at pH 6 or below for reliable protection.

Not dissolving the acid form properly. Pure DHA powder is poorly soluble. If you add it to a lukewarm oil phase, it will not dissolve and you will get crystalline specks in your product. Heat the oil phase to at least 60°C, or use the pre-blended liquid form.

Confusing the acid and salt forms. They have different solubilities, different use rates, and go into different phases. Using the oil-soluble acid form in a water phase will result in poor distribution and weak preservation.

Overdosing the pre-blend. If you are using a DHA + benzyl alcohol blend, the maximum benzyl alcohol in a finished product is 1% (EU regulation). Going heavy on the blend to “be safe” can push you over the limit.

Substitutes

• Phenoxyethanol + ethylhexylglycerin — another popular paraben-free broad-spectrum system. Slightly wider pH tolerance.
• Phenoxyethanol + caprylyl glycol — similar broad coverage, different co-preservative pairing.
• Sodium benzoate + potassium sorbate — natural-origin alternative, but strictly pH-dependent (below 5.5) and narrower spectrum.
• Geogard ECT — COSMOS-certified option for natural formulas. Different active chemistry but fills the same broad-spectrum role.