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Hair dying traces its roots to antiquity with evidence of use in ancient Egypt and the Roman Empire. Today, hair dying is an estimated $7 billion industry worldwide. Altering the natural color of hair is popular with both men and women but does have some health risks.
Hair has two major parts - the hair follicle and the hair shaft. The hair follicle is located at the root of the hair and attaches each hair to the scalp. The hair shaft sticks out of the follicle. Hair follicles contain living cells, but hair shafts do not. Hair color comes from the pigment melanin, which is made by cells in the hair follicle. Hair turns gray when the production of melanin decreases or stops.
Hair dyes remove the natural color and/or add new color to the hair shaft. They can be natural or synthetic. Natural dyes like henna are obtained from plants. Synthetic dyes can be divided into two general categories: temporary/semi-permanent and permanent. Temporary dyes only penetrate the outermost layer of the hair shaft and are easily removed with one shampooing. Semi-permanent and permanent dyes reach deeper into the hair shaft. While semi-permanent dyes are removed with 4-12 shampoos, permanent dyes are resistant to shampooing. Permanent dyes cause chemical changes that increase the penetration of the product into the hair, bleach the natural melanin, and create color molecules that get trapped inside the shaft. These chemical changes can damage the hair. Semi-permanent dyes also contain chemicals that can remove melanin from the hair shaft, but they are not as strong and cause less damage.
Permanent hair dyes are those most frequently associated with health risks. These products typically include an alkalizing agent like ammonia, an oxidizing agent like hydrogen peroxide, a primary intermediate such as paraphenylenediamine (PPD), and coupler molecules like resorcinol. The alkalizing agent helps the product penetrate the outer layer of the hair shaft, and the other ingredients cause the chemical reactions that create color molecules inside the hair shaft.
Even when hair dyes are used as directed, harmful health effects are possible. Up to 25 different ingredients in hair dyes can cause harmful skin effects. One of the main culprits is the primary intermediate PPD. Contact with skin can cause irritation including redness, sores, itching, and burning. Occasionally, allergic reactions occur and involve swelling of the face and neck that causes difficulty breathing. These toxic effects can occur immediately or up to a day after contact with the skin.
Gloves should be worn to limit the skin toxicity of hair dye. Many research studies have evaluated the use of gloves to reduce skin reactions from hair dyes, especially from dyes that contain PPD. One study found that nitrile gloves clearly outperform natural rubber latex, polyethylene, and vinyl gloves. Disposable gloves should never be re-used. Wearing gloves does not protect the scalp, neck, forehead, ears, and eyelids.
Some of the ingredients in hair dyes have been suspected of causing cancer, but there are currently no well-done, human studies that show a definite, increased cancer risk.
Unintentional ingestions of dyes by children usually involve small amounts. Temporary hair dyes, like the kind used at Halloween, should only cause minor irritation to the mouth, some nausea, and maybe some vomiting. Toxicity is increased with semi-permanent and permanent dyes because of their alkalizing and oxidizing agents. More severe irritation of the mouth, throat, and stomach would be expected, and more severe vomiting is also likely. Depending on the product, a chemical burn is possible. Even small amounts of products with primary intermediates like PPD can cause life-threatening allergic reactions including swelling of the tongue and throat and difficulty breathing.
If a temporary dye product gets into the eyes, it would be expected to cause minor irritation. Greater injury is possible with semi-permanent and permanent dyes. The FDA reports eye injuries, including blindness, from permanent hair dye. These products should never be used to color eyebrows or eyelashes.
If you suspect someone has swallowed hair dye, immediately check the webPOISONCONTROL® online tool for guidance or call Poison Control at 1-800-222-1222. If the hair dye is in the eye or on the skin, rinse first with room temperature water for 15 minutes then call Poison Control for guidance.
Karen Dominguez, PharmD
Certified Specialist in Poison Information
Antelmi A, Young E, Svedman C, et al. Are gloves sufficiently protective when hairdressers are exposed to permanent hair dyes? An in vivo study. Contact Dermatitis 2015;72:229-36.
Kim KH, Kabir E, Jahan SA. The use of personal hair dye and its implications for human health. Environ Int 2016;89-90:222-7.
Nohynek GJ, Fautzb R, Benech-Kiefferc F, Toutaina H. Toxicity and human health risk of hair dyes. Food Chem Toxicol 2004;42:517-43.