7. Lead and Mercury
Neurotoxic lead may appear in products as a naturally occurring contaminant of hydrated silica, one of the ingredients in toothpaste, and lead acetate is found in some brands of men's hair dye. Brain-damaging mercury, found in the preservative thimerosol, is used in some mascaras.

8. Nanoparticles
Tiny nanoparticles, which may penetrate the skin and damage brain cells, are appearing in an increasing number of cosmetics and sunscreens. Most problematic are zinc oxide and titanium dioxide nanoparticles, used in sunscreens to make them transparent. When possible, look for sunscreens containing particles of these ingredients larger than 100 nanometers. You'll most likely need to call companies to confirm sizes, but a few manufacturers have started advertising their lack of nanoparticle-sized ingredients on labels.

9. Parabens
(methyl-, ethyl-, propyl-, butyl-, isobutyl-) Parabens, which have weak estrogenic effects, are common preservatives that appear in a wide array of toiletries. A study found that butyl paraben damaged sperm formation in the testes of mice, and a relative, sodium methylparaben, is banned in cosmetics by the E.U. Parabens break down in the body into p-hydroxybenzoic acid, which has estrogenic activity in human breast-cancer cell cultures.

10. Petroleum Distillates
Possible human carcinogens, petroleum distillates are prohibited or restricted for use in cosmetics in the E.U. but are found in several U.S. brands of mascara, foot-odor powder and other products. Look out for the terms "petroleum" or "liquid paraffin."

11. P-Phenylenediamine
Commonly found in hair dyes, this chemical can damage the nervous system, cause lung irritation and cause severe allergic reactions. It's also listed as 1,4-Benzenediamine; p-Phenyldiamine and 4-Phenylenediamine.

12. Hydroquinone
Found in skin lighteners and facial moisturizers, hydroquinone is neurotoxic and allergenic, and there's limited evidence that it may cause cancer in lab animals. It may also appear as an impurity not listed on ingredients labels.