Coal tar dyes are artificial coloring agents made by combining various aromatic hydrocarbons like toluene, xylene, benzene, which are obtained from the distillation of bituminous coal. Coal tars are also made from petroleum distillates. Coal tar is a brown or black liquid of extremely high viscosity. Coal tar is among the by-products when coal is carbonized to make coke or gasified to make coal gas.
These dyes are used in foods, over-the-counter and prescription drugs, textiles, cosmetics, and personal care products like hair dyes, shampoos, and deodorants. Coal tars are also used therapeutically in products said to control dandruff, eczema, psoriasis, seborrheic dermatitis, and other skin disorders, as well as being used to kill and repel head lice. When used as a medication in the U.S., coal tar preparations are considered over-the-counter drug pharmaceuticals and are subject to regulation by the USFDA. Named brands include Denorex, Balnetar, Psoriasin, Tegrin, T/Gel, and Neutar.
Coal tar-derived colours are used extensively in cosmetics, generally identified by a five-digit Colour Index (C.I.) number. The U.S. colour name may also be listed ("FD&C" or "D&C" followed by a colour name and number). P-phenylenediamine is a particular coal tar dye used in many hair dyes. Darker hair dyes tend to contain more phenylenediamine than lighter colours. P-phenylenediamine has been linked to tumours in laboratory tests conducted by the U.S. National Cancer Institute. Hair dye manufacturers must label any product containing coal tar hair dyes with a warning that the product may cause skin reactions in certain allergic individuals. There’s also evidence that artificial colors increase hyperactivity, ADHD and learning difficulties in children. Other studies have implicated coal tars in lung and skin cancers (though a direct relationship remains unproved). According to the International Agency for Research on Cancer, preparations that include more than five percent of crude coal tar are Group 1 carcinogens. California requires OTC coal tar shampoos, lotions and creams that contain more than 0.5 percent coal tar to be labeled with cancer warnings. Coal tar causes increased sensitivity to sunlight, so skin treated with topical coal tar preparations should be protected from sunlight. The residue from the distillation of high-temperature coal tar, primarily a complex mixture of three or more membered condensed ring aromatic hydrocarbons, was listed on 28 October 2008 as a substance of very high concern by the European Chemicals Agency.
Coal tars are also known as naphtha, high solvent naphtha, naphtha distillate, benzin B70, or petroleum benzin.
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