Potassium Sorbate

Potassium sorbate is an antifungal preservative typically used around ~0.1–0.3% (sometimes up to ~0.5%) and is generally well tolerated, but it has a documented history of stinging/irritation in leave-on products, especially at lower pH where sorbic acid is more active. Patch test data and real-world use show occasional irritant reactions (and rarer allergic contact dermatitis), with higher risk in eczema-prone or barrier-impaired skin. Given those vulnerable populations and the frequency of use across routines, I rate it as mild rather than “gentle.” Safety Notes: In commercial cosmetics, potassium sorbate is most often used as a supplemental preservative in water-based, low-pH systems (effective mainly below ~pH 6), with many leave-on lotions/serums and rinse-off cleansers using ~0.05–0.30% when paired with other preservatives or multifunctionals. The lowest market observations are around 0.05% in “mild/natural” or multi-hurdle preserved formulas, while the highest OTC consumer products (including some natural/organic-style creams, toners, and masks) reach about 0.8–1.0% to compensate for limited preservative options and higher microbial risk, constrained by solubility/irritation and pH requirements.