Pyrocatechol

What Is It?

Pyrocatechol, also called catechol, is a chemical coupling agent that occurs as a colorless to white crystalline solid. Pyrocatechol is used in the formulation of permanent hair dyes, colors, and tints.

Why Is It Used?

Pyrocatechol helps to impart a color to hair. The exact color obtained will depend on the other ingredients that are used in the preparation and the starting color of the hair.

Scientific Facts

Pyrocatechol is used in permanent hair coloring systems where color is produced inside the hair fiber. This is accomplished through careful formulation of the product so that the ingredients interact in a highly controlled process.
Safety Information

The safety of Pyrocatechol has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel evaluated the scientific data and concluded that Pyrocatechol was unsafe for use in leave-on products, and that the available data were insufficient to determine whether Pyrocatechol was either safe or unsafe as used in hair dyes.

CIR Safety Review:

When this ingredient was first reviewed by the CIR Expert Panel, it was concluded that Pyrocatechol was safe for use in formulations designed for discontinuous, brief use followed by rinsing from the skin and hair at concentrations of up to 1.0%. This amendment to that report was prepared in order to incorporate the results from several studies, including those reporting immunologic, carcinogenic, and cocarcinogenic effects of Pyrocatechol. In vitro, Pyrocatechol has been shown to affect several immunologic and other properties of bone marrow cells, both alone and when combined with hydroquinone. Pyrocatechol, when produced as a liver metabolite of benzene, has been reported to concentrate in the bone marrow and to adversely affect blood precursor cells. These effects are somewhat species specific. Dermal exposure to Pyrocatechol affects the number and distribution of immune cells in the skin at the site of exposure, but is not associated with a change in contact sensitivity.

Oral exposure to Pyrocatechol did result in an increase in developmental effects. Pyrocatechol was tested in a number of mutagenesis systems. Both negative and positive results were observed. Carcinogenicity studies of Pyrocatechol in the diet were also conducted. While adenomatous hyperplasia was noted, adenocarcinomas were seen in males and females in one study only. In cocarcinogenesis studies there was a similar pattern of hyperplasia and adenomas of the glandular stomach in the groups exposed to Pyrocatechol alone. When administered with several other carcinogens, Pyrocatechol had a cocarcinogenic effect. Pyrocatechol was not a tumor promoter in dermal studies.

Based on these data and the significant potential for skin absorption of Pyrocatechol in leave-on preparations, the CIR Expert Panel concluded that Pyrocatechol is unsafe for use in leave-on cosmetic formulations. Pyrocatechol used in a rinse-off application such as hair dyes may not present a similar concern if Pyrocatechol is completely and rapidly oxidized resulting in limited dermal exposure. Because no data were available, to indicate the extent and rate of oxidation of this ingredient when it is used in hair dyes, it was concluded that there were insufficient data to support the safety of this ingredient.

More information about the safety of hair dyes.

Health Canada does not permit the use of Pyrocatechol (catechol) in cosmetics and personal care products.

http://www.hc-sc.gc.ca/cps-spc/person/cosmet/info-ind-prof/_hot-list-cri…

Pyrocatechol is listed as Catechol in the Cosmetics Directive of the European Union and must not form part of the composition of cosmetics and personal care products (see Annex II).

Link to the EU Cosmetic Regulation: http://europa.eu/legislation_summaries/consumers/product_labelling_and_packaging/co0013_en.htm

More Scientific Information

Hair dyeing formulations belong to three categories – temporary, semi-permanent and permanent coloring of hair. The permanent hair dyeing formulations are often referred to as oxidative hair dyes which are generally marketed as two-component products. One component contains the compounds (precursors) that become the colorants and the other component is a stabilized solution of hydrogen peroxide. The two components are mixed immediately prior to use.

The precursors and peroxide diffuse into the hair shaft, where color formation takes place after the ingredients combine to produce the coloring mixture. The precursors are oxidized by the hydrogen peroxide to form the colorant molecules. These molecules are too large to escape from the hair structure. The hydrogen peroxide in the oxidative hair dye product also serves as bleaching agent for the natural pigment of the hair. The color that is formed depends on the precursors and direct dyes present in the dyeing solution, pH of the dyeing solution and the time of contact of the dyeing solution with the hair. Pyrocatechol is a 2-hydroxy substituted phenol. In cosmetics and personal care products, Pyrocatechol functions as a hair colorant.
Resources

The FDA’s factsheet on Hair Dye Products http://www.fda.gov/Cosmetics/ProductandIngredientSafety/ProductInformati…

Search the FDA Code of Federal Regulations http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm

The International Agency for Research on Cancer’s Summary and Evaluation of Catechol http://www.inchem.org/documents/iarc/vol71/012-catechol.html

EU Cosmetic Ingredients Inventory http://ec.europa.eu/consumers/cosmetics/cosing/