Zinc Sulfate

Zinc sulfate is an astringent inorganic salt used at low levels in topical products, but it is water-soluble and can sting and irritate compromised or eczematous skin, especially around mucosa or on broken barriers. Clinically, zinc salts are not among the most common allergens, yet they are well-documented to cause dose- and exposure-dependent irritation (burning, dryness, erythema) in sensitive populations. Given real-world cumulative use with other actives and the heightened risk in barrier-impaired patients, a moderate irritancy score is warranted and patch testing is advisable. Safety Notes: In consumer skincare, zinc sulfate is most often used at very low levels (~0.01–0.1%) in leave-on soothing/blemish or anti-redness products as a mild astringent/antimicrobial and to support preservative systems, with some products using trace amounts as a label-claim support ingredient. Higher-strength OTC products (typically targeted acne/spot treatments and some scalp/skin tonics) are observed around 0.5–2.0%, above which irritation and solubility/pH constraints become more limiting for general cosmetic use. Rinse-off cleansers can also sit in the lower-mid portion of this range, but the upper end is more commonly seen in leave-on targeted treatments available to consumers.