Selenium Sulfide

Selenium sulfide is an FDA-approved anti-fungal for dandruff, seborrheic dermatitis, and tinea versicolor, and its verdict is conditional because the same compound carries a carcinogen listing by a route your shampoo does not use. The US National Toxicology Program lists selenium sulfide as reasonably anticipated to be a human carcinogen, and that listing rests on liver tumors in rodents that were fed it by stomach tube; the program notes that applying it to skin did not produce tumors. That distinction is the whole point: on an intact scalp, rinsed off, a one percent lotion is not measurably absorbed, so the swallowing hazard does not attach to normal use. Europe treats it the same conditional way rather than banning it: while selenium compounds are generally kept out of cosmetics, selenium disulfide is specifically permitted up to one percent in anti-dandruff shampoo, and the product must carry the warning "Contains selenium disulphide. Avoid contact with eyes or damaged skin." That enforced cap and label are the consumer-facing signal, and they line up with the drug label's own caution that absorption rises on inflamed or broken skin, along with its advice against use in pregnancy for lack of data. So it is fine used as directed, as a rinse-off treatment on unbroken skin at the capped strength, and the times to set it aside are pregnancy, damaged skin, and anything that would put it in the mouth.