Hair Dyes: Fact Sheet
Hair dye products may be divided into three categories, i.e., permanent, semi-permanent and temporary hair colors. Permanent hair colors are the most popular hair dye products. They may be further divided into oxidation hair dyes and progressive hair dyes. Oxidation hair dye products consist of (1) a solution of dye intermediates, e.g., p-phenylenediamine, which form hair dyes on chemical reaction, and preformed dyes, e.g., 2-nitro-p-phenylenediamine, which already are dyes and are added to achieve the intended shades, in an aqueous, ammoniacal vehicle containing soap, detergents and conditioning agents; and, (2) a solution of hydrogen peroxide, usually 6%, in water or a cream lotion.
The ammoniacal dye solution and the hydrogen peroxide solution, often called the developer, are mixed shortly before application to the hair. The applied mixture causes the hair to swell and the dye intermediates (and preformed dyes) penetrate the hair shaft to some extent before they have fully reacted with each other and the hydrogen peroxide and formed the hair dye.
Progressive hair dye products contain lead acetate as the active ingredient. Lead acetate is approved as a color additive for coloring hair on the scalp at concentrations not exceeding 0.6% w/v, calculated as metallic lead (21 CFR 73.2396). Bismuth citrate, the other approved color additive (21 CFR 73.2110), is used to a much lesser extent. Progressive hair dyes change the color of hair gradually from light straw color to almost black by reacting with the sulfur of hair keratin as well as oxidizing on the hair surface.
Semi-permanent and temporary hair coloring products are solutions (on rare occasions dry powders) of various coal-tar, i.e. synthetic organic, dyes which deposit and adhere to the hair shaft to a greater or lesser extent. Temporary hair colors must be reapplied after each shampooing. The vehicle may consist of water, organic solvents, gums, surfactants and conditioning agents. The coal-tar dyes are either listed and certified colors additives or dyes for which approval has not been sought. The dyes may not be non-permitted metallic salts or vegetable substances.
A hair dye product containing a non-approved coal-tar color (but not a non-approved metallic or vegetable dye) which is known to cause adverse reactions under conditions of use cannot be considered adulterated if the label bears the caution statement provided in section 601(a) of the FD&C Act and offers adequate directions for preliminary patch testing by consumers for skin sensitivity. The caution statement reads as follows:
Caution - This product contains ingredients which may cause skin irritation on certain individuals and a preliminary test according to accompanying directions should first be made. This product must not be used for dyeing the eyelashes or eyebrows; to do may cause blindness.
If the label of a coal-tar color-containing hair dye product does not bear the caution statement of section 601(a) and the patch testing directions, it may be subject to regulatory action if it is determined to be harmful under customary conditions of use.
Several coal-tar hair dye ingredients have been found to cause cancer in laboratory animals. In the case of 4-methoxy-m-phenylenediamine (4-MMPD, 2,4-diaminoanisole) which had also been demonstrated in human and animal studies to penetrate the skin, the agency considered the risk associated with its use in hair dyes a "material fact" which should be made known to consumers. The regulation requiring a label warning on hair dye products containing 4-MMPD published in October 1979 was to become effective April 16, 1980. The regulation required that hair dyes containing 4-MMPD bear the following warning:
Warning - Contains an ingredient that can penetrate your skin and has been determined to cause cancer in laboratory animals.
Some hair dyes manufacturers held that the potential risk was too small to be considered "material" and challenged the validity of the regulation in court. The agency decided to reconsider its earlier position, entered into a consent agreement with hair dye manufacturers, and stayed the effectiveness of the regulation until completion of an assessment of the carcinogenic risk of 4-MMPD in accordance with scientifically accepted procedures.
In addition to 4-MMPD, the following other hair dye ingredients have been reported to cause cancer in at least one animal species in lifetime feeding studies: 4-chloro-m-phenylenediamine, 2,4-toluenediamine, 2-nitro-p-phenylenediamine and 4-amino-2-nitrophenol. They were also found to penetrate human and animal skin.