Anti-dandruff shampoos may contain selenium; other toiletries and cosmetics, such as hair colouring products, may contain toxic substances; disposable batteries contain mercury or cadmium; household cleaners and drugs often contains cocktails of poisons; even simple vitamins and foodstuffs may be toxic in sufficient doses, particularly to children. Soaps and detergents are toxic if ingested.
Contrary to some earlier studies, 1994 analysis of data from 573,369 women in the USA found that the only link of hair dye to fatal cancer came in 0.6 percent of the women who used black hair dye for 20 years or more. These women had about a four times greater risk of developing non-Hodgkin's lymphoma or multiple melanoma that women who did not use the dye.