Acute toxicity of Zinc pyrithione to human skin cells in vitro.

Zinc pyrithione introduced into cultures of rapidly proliferating NCTC 2544 human skin epithelial cells and normal human skin fibroblasts had a rapid cytotoxic effect even at very low concentrations (0.1-0.5 microgram/ml); there was no dose-dependent suppression of cell proliferation and no apparent interference with mitosis. Sodium pyrithione had a similar effect. Zinc oxide and zinc sulphate were at least 100 times better tolerated than zinc pyrithione, but no stimulatory effect on cell growth was detected with low concentrations of either compound. These results suggest that zinc pyrithione's action against dandruff is more likely to arise from a non-specific toxicity for epidermal cells than by an anti-mitotic effect or by remedying a local zinc deficiency.