What it does
The EU's CosIng database describes potassium sorbate as an organic salt, chemically potassium (E,E)-hexa-2,4-dienoate, and lists two functions: preservative and fragrance.1 A preservative, in CosIng's definition, is exclusively or mainly intended to inhibit the development of microorganisms in the cosmetic product itself.2 It protects the product, not the skin.
A review of cosmetic preservation groups sorbic acid with the organic acid preservatives, and names pH as a major factor in how well organic acids work, because it determines how much of the acid is present in its undissociated form.3 An ingredient list does not state a product's pH, so the list alone cannot show how effective the preservative is in that formula.
The EU limit
Potassium sorbate falls under Annex V, entry 4, the entry for hexa-2,4-dienoic acid and its salts. The entry names four ingredients, Sorbic Acid, Calcium Sorbate, Sodium Sorbate and Potassium Sorbate, and sets a single maximum of 0.6% in the ready-for-use product, counted as the acid. It sets no restriction by product type and requires no warning on the label.4
A cosmetic may only be preserved with substances listed in Annex V, used within their conditions, and a listed substance must keep to those conditions even when it is used for another purpose (Article 14(1)(d)).4 The cosmetic preservatives guide sets entry 4 beside the other common preservatives and their limits.
Also a food additive: E 202
The EU's list of permitted food additives includes potassium sorbate as E 202, after sorbic acid, E 200.5 Food and cosmetics are regulated separately, so the E number has no bearing on the cosmetic limit above.
Skin reactions
Contact urticaria, hives where a substance touches the skin, is uncommon: a German study found it in 0.28% of nearly 160,000 patients in a network of dermatology departments and in 0.34% of patients at one university allergy unit. Among the 16 cases at that unit, the most frequent causes were natural rubber latex and sorbic acid, the acid form of this preservative.6 These were patients referred to dermatology and allergy clinics, not the general population.
How it appears on a label
As Potassium Sorbate. Sorbic Acid and Sodium Sorbate appear under their own names and share the same entry and limit.4 The list gives no concentration, so it cannot show how close a product is to 0.6%. To see which names on a list are preservatives, paste it into the ingredient checker, or compare two products with the ingredient list comparison tool.