Zinc pyrithione vs Potassium Sorbate: which is worse?

What is Zinc pyrithione?

Zinc pyrithione is an antifungal and antibacterial active in dandruff shampoos.

What is Potassium Sorbate?

Potassium sorbate is the potassium salt of sorbic acid, a naturally occurring short-chain fatty acid originally derived from the mountain ash berry (Sorbus aucuparia). Commercial potassium sorbate is synthetically produced by reacting sorbic acid with potassium hydroxide. It is the most widely used food preservative globally.

Documented risks

Zinc pyrithione: Reclassified as a reproductive toxicant in the EU and banned as a cosmetic preservative in 2022; still a key US OTC dandruff active.

Potassium Sorbate: Potassium sorbate has a generally good safety profile compared to other synthetic preservatives. EFSA's 2015 re-evaluation maintained the ADI at 3 mg/kg body weight, finding no significant carcinogenicity or genotoxicity. However, some human and in vitro studies have documented concerns. A 2010 study in Toxicology in Vitro found potassium sorbate was genotoxic (caused DNA strand breaks) in human blood cells at concentrations achievable in food. The study found it damaged peripheral blood lymphocytes. A 2014 study in Food and Chemical Toxicology found potassium sorbate caused DNA damage in human lymphocytes at food use concentrations. Contact dermatitis and allergic reactions from topical use are documented. At very high doses in animal studies, liver and kidney effects have been observed. The general regulatory consensus is that potassium sorbate is one of the safer food preservatives, but the in vitro genotoxicity findings deserve attention.