Over 50 million women in the U.S. use hair dye regularly. Teenagers are particularly vulnerable, and it is believed that the popularity of dyeing hair and the obsession with "youth culture" are to blame . However, hair dyes are some of the most toxic cosmetic products available. The chemicals found in hair dye have been shown to have a variety of harmful effects in scientific experiments. Use of hair dye has been linked to allergic reactions, respiratory disorders and even cancer . About 400 out of the 456 hair colors ranked in the Skin Deep cosmetics database of the Environmental Working Group are considered high hazard, which means they contain toxic ingredients linked to cancer, developmental and reproductive toxicity, neurotoxicity, immunotoxicity, organ toxicity, in addition to the allergic problems already discussed. Of the 169 permanent hair dyes on the market, 159 are mutagenic.

There is also an increased risk of lung, uterine, ovarian, breast, digestive and respiratory cancer among those who use hair dyes. A 2001 USC study identified the highest risk groups for susceptibility for bladder cancer due to hair dyes. These include women who have used permanent dyes once a month or more for a year or longer and those who have worked as hair dressers or barbers for ten years or more. If the dyes were used for 15 years or more, the risk was tripled. The darkness of the dye also increased the risk.” A separate study conducted in 2008 by the National Cancer Institute found similar results. The study discovered a connection between hair dyes, especially dark ones, and the group of cancers that impact blood and lymph nodes, such as non-Hodgkin's lymphoma and multiple myeloma. It was found that women who started using hair dye, particularly darker colors, before 1980 had an increased risk of developing the disease.

The darker dyes are more challenging as they contain greater levels of chemicals. The National Institute for Occupational Safety and Health (NIOSH) stated that skin contact with PPD should be prevented in order to avoid the allergic reactions, and indeed, the FDA has NOT approved its use for direct skin application. This is an oxymoron, though, as it is next to impossible to avoid contact with the skin when applying hair color.

The most problematic hair dye ingredient is a family of chemicals called Arylamines. Arylamines are a known risk factor for bladder cancer and have been found to cause cancer in experimental animals. One of these is p-phenylenediamine (PPD) which is listed on the box of even non-permanent "natural" products.

The most common allergic reactions to hair dye chemicals are dermatitis of the eyes, ears, scalp and face, which may include a rash, extreme swelling and a severe burning sensation on the scalp. More severe reactions include cross-sensitization, when you become sensitive to PPD and all of its chemical cousins, and in rare cases, death. As is the case with many other products that have potentially dangerous chemicals, the European Union has already taken action and banned 22 toxic hair dye substances in 2007 alone. The banned substances include:

6-Methoxy-2,3-Pyridinediamine and its HCl salt

2,3-Naphthalenediol

2,4-Diaminodiphenylamine

2,6-Bis(2-Hydroxyethoxy)-3,5-Pyridinediamine

2-Methoxymethyl-p-Aminophenol

4,5-Diamino-1-Methylpyrazole and its HCl salt

4,5-Diamino-1-((4-Chlorophenyl)Methyl)-1H-Pyrazole Sulfate

4-Chloro-2-Aminophenol

4-Hydroxyindole

4-Methoxytoluene-2,5-Diamine and its HCl salt

5-Amino-4-Fluoro-2-Methylphenol Sulfate

N,N-Diethyl-m-Aminophenol

N,N-Dimethyl-2,6-Pyridinediamine and its HCl salt

N-Cyclopentyl-m-Aminophenol

N-(2-Methoxyethyl)-p-phenylenediamine and its HCl salt

2,4-Diamino-5-methylphenetol and its HCl salt

1,7-Naphthalenediol

3,4-Diaminobenzoic acid

2-Aminomethyl-p-aminophenol and its HCl salt

Solvent Red 1 (CI 12150)

Acid Orange 24 (CI 20170)

Acid Red 73 (CI 27290)