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Coal tar is a brown or black liquid of high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal is carbonized to make coke or gasified to make coal gas. Coal tars are complex and variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds. 
Additional recommended knowledge
Being flammable, coal tar is sometimes used for heating or to fire boilers. Like most heavy oils, it must be heated before it will flow easily.
It can be used in medicated shampoo, soap and ointment, as a treatment for dandruff and psoriasis, 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 an OTC (over-the-counter drug) pharmaceutical and are subject to regulation by the United States Food and Drug Administration. Name brands include Balnetar, Psoriasin, and Tegrin.
The artificial sweetener Saccharin is a derivative of coal tar.
Despite this, the National Psoriasis Foundation claims coal tar is a valuable, safe and inexpensive treatment option for millions of people with psoriasis and other scalp conditions,  the FDA agrees with this and states that coal tar concentrations between 0.5% and 5% are safe and effective for psoriasis and that no scientific evidence suggests that the coal tar in the concentrations seen in non-prescription treatments is carcinogenic. The NPF states that coal tar contains approximately 10,000 different chemicals, of which only about 50% have been identified , and the composition of coal tar varies with its origin and type of coal (eg: lignite, bituminous or anthracite) used to make it, so much further research remains to be done on coal tar and its derivatives.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Coal_tar". A list of authors is available in Wikipedia.