[2][4] Medicinally it is a topical medication applied to skin to treat psoriasis and seborrheic dermatitis (dandruff).

[6][8] Circa 1850, the discovery that it could be used as the main raw material for the synthesis of dyes engendered an entire industry.

[14][better source needed] Most of the chemical compounds are polycyclic aromatic hydrocarbon:[15][16] Others: benzene, toluene, xylenes, cumenes, coumarone, indene, benzofuran, naphthalene and methyl-naphthalenes, acenaphthene, fluorene, phenol, cresols, pyridine, picolines, phenanthracene, carbazole, quinolines, fluoranthene.

[12] Coal tar is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.

When used in the extemporaneous preparation of topical medications, it is supplied in the form of coal tar topical solution USP, which consists of a 20% w/v solution of coal tar in alcohol, with an additional 5% w/v of polysorbate 80 USP; this must then be diluted in an ointment base, such as petrolatum.

In its original development by Edgar Purnell Hooley, tarmac was tar covered with granite chips.

[citation needed] Coal tar is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement.

[47] Evidence is inconclusive whether medical coal tar, which does not remain on the skin for the long periods seen in occupational exposure, causes cancer, because there is insufficient data to make a judgment.

[20] The PAHs found in coal tar and air pollution induce immunosenescence and cytotoxicity in epidermal cells.

[48] Long-term skin exposure to these compounds can produce "tar warts", which can progress to squamous cell carcinoma.

[13] Coal tar was one of the first chemical substances proven to cause cancer from occupational exposure, during research in 1775 on the cause of chimney sweeps' carcinoma.

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 13 January 2010 as a substance of very high concern by the European Chemicals Agency.

The Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit) to 0.2 mg/m3 benzene-soluble fraction over an 8-hour workday.

The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.1 mg/m3 cyclohexane-extractable fraction over an 8-hour workday.