Nearly 7 out of every 10 American women color their hair to hide gray roots, explore whether blondes have more fun, or just try something new. But given that the ingredients lists on hair dyes typically read like chemistry textbooks, we have to wonder: Are dyes actually safe to put on our heads?

For the most part, the answer is a qualified yes -- at least as far as cancer is concerned. Dozens of studies have ruled out connections between hair dye and bladder and breast cancer, brain tumors, and non-Hodgkin's lymphoma.

Skin Concerns
Health experts still stop short of giving dyes a clean bill of health, though, partly because of the skin reactions they can cause. Kathleen Davis, M.D., an integrative dermatologist in New York City, says that contact dermatitis from p-Phenylenediamine (PPD), a known allergen, can result in temporarily swollen eyelids or rashes around the hairline. Since PPD is more concentrated in darker shades, it's a particular concern for brunettes.

Would-be blondes have bleach to blame for blisters and burning on sensitive scalps as well as lightheadedness. But the bleaching processes have improved: "The amount of ammonia in dyes and bleaches is very slight now compared with 20 years ago," says Eva Scrivo, a New York City colorist, referring to the potentially skin-irritating chemical used in products to help color penetrate hair. "In the '60s, products contained 20 percent ammonia, but now they're down to 1.5 percent." She says some new bleaches don't contain any ammonia at all -- and still work well if you have light to medium brown hair. If you're worried, try a patch test before subjecting your whole scalp to the dye in question, or take a lighter approach. "With highlights," Scrivo says, "nothing touches the scalp."