Sodium Benzoate and Potassium Sorbate, Explained: What the EU's 0.5 and 2.5 Percent Benzoic Acid Limits and 0.6 Percent Sorbic Acid Limit Mean, and Why pH Matters

Two preservative families in the EU rulebook

The EU Cosmetics Regulation (EC) No 1223/2009 lists permitted preservatives in Annex V. Benzoic acid and its sodium salt are entry 1, and sorbic acid and its salts, including potassium sorbate and calcium sorbate, are entry 4. The UK keeps the same annex. These are positive lists: an ingredient may be used as a preservative only up to the stated limit.

The benzoic acid limits: 0.5 and 2.5 percent

For benzoic acid and sodium benzoate the maximum is 2.5 percent in rinse-off products other than oral care, 1.7 percent in oral care products and 0.5 percent in leave-on products. A serum, moisturizer or sunscreen is leave-on, so the lowest number is the one that applies to most of what you apply and keep on your skin.

The sorbic acid limit: 0.6 percent

Sorbic acid and its salts share a single limit of 0.6 percent in the finished product, whether the product is leave-on or rinse-off. The limit is for all sorbate sources added together, so a formula cannot use sorbic acid and potassium sorbate each up to 0.6 percent.

"Expressed as acid" changes the arithmetic

Both limits are written as the acid, not the salt. Sodium benzoate is heavier than benzoic acid because it carries a sodium atom, so a formula can contain a little more of the salt than the headline number suggests. Using molar masses (benzoic acid about 122.1, sodium benzoate about 144.1), 0.5 percent as acid works out to roughly 0.59 percent sodium benzoate. For sorbic acid (about 112.1) and potassium sorbate (about 150.2), 0.6 percent as acid is roughly 0.80 percent potassium sorbate. These conversions are our own arithmetic, not figures printed in the regulation.

Why pH decides whether they work

These preservatives act mainly in their undissociated acid form, which is why they are used in acidic products. Benzoic acid has a pKa near 4.2 and sorbic acid near 4.8, so in a product with a higher pH most of the preservative is in the salt form that does little. A formula can be within the legal limit and still be poorly preserved, which is why the legal ceiling is not a guarantee of protection and why formulators check a product's pH and test its preservation.

What the label position tells you

Ingredient lists run in descending order of weight only down to 1 percent. Anything at or below 1 percent can appear in any order. Because the benzoate and sorbate limits in leave-on products are 0.5 and 0.6 percent as acid, both normally sit in that unordered tail. Seeing them early or late on a list tells you nothing about how much is in the jar. The same logic applies to phenoxyethanol and its 1 percent EU limit.

In the US, and what this guide does not claim

The US FDA does not require premarket approval of cosmetic ingredients other than color additives, and we did not find a numeric FDA limit for these two preservatives, so the EU numbers are the benchmark used here. This guide does not claim either ingredient treats, prevents or causes any skin condition. Like any ingredient, a preservative can irritate some skin, so try a new product on a small area first with our patch-test method.

Short version

In the EU, benzoic acid and sodium benzoate are capped at 0.5 percent as acid in leave-on products and 2.5 percent in rinse-off, and sorbic acid and its salts at 0.6 percent as acid. They need an acidic formula to work, and label position says nothing about their amount. For other preservative families see parabens. This article is educational, not medical advice: patch-test new products first, and ask a dermatologist about acne, rosacea or any persistent skin problem.