Sodium Benzoate

What it is

Sodium benzoate is the sodium salt of benzoic acid and appears in nine products in this lexicon. What is effective is not the salt but the free acid that forms from it in an acidic environment. The performance of this preservative therefore depends directly on the pH of the formulation: below about pH 5 it works, in the neutral range hardly at all.

That explains why it almost always appears in company. In this lexicon it is found six times together with phenoxyethanol and four times with potassium sorbate. It also explains why citric acid so often stands at the end of the same list — it creates the acidic range in which the benzoate can work at all.

Why

• Why the classification reads “low risk”: benzoate is applied externally, predominantly in rinse-off products and in small amounts. The substance has been in use for decades in both food and cosmetics and is thus among the longest-observed preservatives there are.
• The actual finding is one about efficacy, not about safety. Only the undissociated acid is active, and its share rises as the pH falls. A formulation close to the neutral range contains the substance according to the list but gets little out of it. The pH cannot be read from the ingredient list.
• An observation from the product range of this lexicon, made with due restraint: in Schwarzkopf IGORA ROYAL Absolutes, sodium benzoate and ascorbic acid appear together in the list. For beverages it is well documented that traces of benzene can form from this pairing — but only under particular conditions: warmth, light and free metal ions over prolonged storage.
• The same list also contains tetrasodium EDTA, that is, precisely the chelating agent that binds free metal ions and thereby suppresses the reaction described. In addition, a hair colour is not a beverage: it is mixed, applied and rinsed out within an hour, not stored warm for months and drunk. Whether the finding has any significance for cosmetics at all is not documented — it therefore sits under the open points and not in the assessment.
• On the stated origin: the short field says “natural”. Benzoic acid does occur in plants, but the sodium salt for food and cosmetics is manufactured. Within this lexicon the entry also contradicts potassium sorbate, which is listed as “synthetic” on a comparable footing. The entry remains unchanged for now, because the same question has already been decided for benzoic acid; it is expressly named here.

When the assessment differs

• Known intolerance to benzoates: it is described and concerns the same substance group as benzoic acid, which has its own record in this lexicon.
• Irritated or broken scalp skin: with a disturbed skin barrier the assumption of low uptake does not simply hold.
• Products that stay on the hair: with mousse and hair colour the contact time does not end with rinsing.
• Very acidic products: this is where the substance is most effective — and at the same time where the highest concentration of the free acid is present.
• Occupational contact: daily use on many heads means a higher total exposure on the hands.

Open questions

• Concentration in the specific product: not available.
• pH of the specific formulation: not documented and not readable from the ingredient list. It determines the effectiveness of this substance.
• Significance of the pairing with ascorbic acid for cosmetics: not documented. The studies on benzene formation come from the beverage sector and concern warmth, light and metal ions over prolonged storage. A transfer to a hair product has not been examined here.
• Stated origin in the short field: reads “natural” and thus differs from potassium sorbate. The question is named in the fourth point above and reserved for a decision.
• Regulatory status: not checked; statements on use and maximum levels are not quoted second-hand.

Sources for this assessment

• Bundesinstitut für Risikobewertung: Indications of the possible formation of benzene from benzoic acid in foods. Stellungnahme mit Auswertung der Untersuchungen von McNeal u. a. zur Benzolbildung aus Benzoat und Ascorbinsäure unter Wärme, UV-Licht und Metallionen. Behördliche wissenschaftliche Stellungnahme, abgerufen am 10.09.2026.

Related substances

Applies to: Preservation and solvents

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

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