Benzoic Acid

What it is

Benzoic acid is one of the oldest and longest-used preservatives. In water-containing products such as shampoos, conditioners and colour creams it prevents microbes from multiplying. What matters for the effect is pH: only the uncharged, acidic form works against microorganisms. In a neutral or alkaline formulation the substance would be largely ineffective.

Preservation is a protective function. A water-based product that stands in the bathroom for weeks or months and is regularly touched by hands and water is, without preservation, a breeding ground. Doing without a preservative is therefore not a neutral decision but a trade against a different risk.

Why

• The pH determines effectiveness. This is not a detail: the same amount of benzoic acid can preserve reliably in an acidic formulation and achieve practically nothing in a neutral one. The ingredient list alone therefore does not show whether a product is well preserved.
• The protective benefit belongs in the assessment. Preservation prevents microbial growth in a product used over weeks. Avoiding preservatives across the board trades a very small, well-studied risk for one that is harder to control — contaminated cosmetics are a real case of harm, not a theoretical one.
• Why the classification reads “low risk”: because of the small use levels, the long history of use and the external application. Irritation is possible at high concentration and low pH; at the levels usual in cosmetics that is not the typical observation.
• Not transferable: the familiar discussion about intolerance to benzoates comes overwhelmingly from food, where the substance is swallowed. Route of uptake and quantity are different there. Transferring it to external use without a separate examination would be methodologically inadmissible.
• Equally not transferable: the reports of benzene forming in drinks where benzoate and ascorbic acid met. That concerns a particular reaction in a particular setting. For cosmetic formulations the question has not been examined here and is therefore neither claimed nor ruled out.

When the assessment differs

• Documented intolerance to benzoates: the product is then unsuitable for that person. That is a statement about the person, not about the quality of the product.
• Irritated, broken or inflamed scalp skin: an acidic environment can sting there.
• Leave-on compared with rinse-off products: longer contact time.
• Eye contact: irritating with acidic preparations.
• Children and infants: not assessed here; separate standards apply to these groups.

Open questions

• Concentration and pH of the actual product: not available. The pH matters particularly here because it determines whether the preservation works.
• Regulatory status: rules on permitted maximum levels exist for preservatives. They have not been checked here and are deliberately not quoted second-hand.
• Origin in the short field: it reads “natural (plants/vitamins)”. Benzoic acid does occur naturally, but the raw material used in cosmetics is manufactured industrially. The entry is not documented here but remains unchanged by decision of 08.09.2026; it matches the same open point as for ascorbic acid.
• Reaction with ascorbic acid: not evaluated. The note above delimits a transfer from the food domain; it does not replace an examination for cosmetic formulations.

Related substances

Applies to: Preservation and solvents

• Alcohol Denat. — Preservative, solubiliser
• Benzyl Alcohol — Preservative, fragrance component
• Ethylhexylglycerin — Skin-conditioning, preservative booster
• Phenoxyethanol — Preservative

Further substances from the same group for which a long-form assessment already exists.