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Coal tar

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Coal tar
Clinical data
Trade namesBalnetar, Cutar, others
Other namesliquor carbonis detergens (LCD)
liquor picis carbonis (LPC)[1]
AHFS/Drugs.comMultum Consumer Information
Routes of
administration		Topical
ATC code
Legal status
Legal status
  • US: OTC / Rx-only
Identifiers
CAS Number
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ECHA InfoCard100.029.417 Edit this at Wikidata

Coal tar is a viscous dark liquid that is a by-product of deriving coke and coal gas from coal.[2][3] Coal tar has long been a source of useful chemicals as well as a general wood preservative. It has some useful medicinal properties.

History

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Coal tar has been produced since about 1665.[4] Much later, in the production of coke and illumination gases ("town gas"), it was an undesirable byproduct. Soon it was found to be a source of solvents.[5] Around 1850, it was discovered that it could be used as a source of many organic compounds. Its use as a precursor to dyes engendered an entire industry.[6] In 1854 Frederick Crace Calvert, "an eminent English chemist," made the extraordinary statement before the Society of Arts that "ere long, some valuable dyeing substances would be prepared from coal."[7] Coal tar was used for medical purposes as early as the 1800s.[8] Coal tar was a component of the first sealed roads. In its original development by Edgar Purnell Hooley, tarmac was tar covered with granite chips. Later the filler used was industrial slag.

Economics

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The value of the trade in coal tar is around US$20 billion per year (2023).[9] As of 2011, 30M tons of coal tar were obtained per year, half of which was processed as a source of chemicals.

Some British companies included:[10][11]

Production

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Coal tar is produced through thermal destruction (pyrolysis or carbonization) of coal, usually with the objective of obtaining coke, which is heavily used in the production of iron and steel. The composition of coal tar varies with the process and type of coal used – lignite, bituminous or anthracite. Most commonly, bituminous coal is used. The tar is further processed, generating fractions of various applications.[12] Coal tar is a black or dark brown liquid or a high-viscosity semi-solid.[13]

Uses

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Coal tars have the following major uses:

  • production of carbon-based electrodes for aluminium processing
  • source of valuable organic compounds including naphthalene, phenanthrene, acenaphthene, pyrene, carbazole, quinoline, phenols
  • Wood preservatives
  • resins for paints and coatings.[5]

Chemical products

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Coal tar is a major source of organic compounds. This application complements the petrochemical industry, which mainly produces alkanes and alkenes. It is a source of polycyclic aromatic hydrocarbons:

Many of these chemicals are precursors to dyes (notably tartrazine/Yellow #5), and photographic materials.[18]

Specialty carbons

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  • As a source of carbon black.[19]
  • As a binder in manufacturing graphite; a considerable portion of the materials in "green blocks" is coke oven volatiles (COV). During the baking process of the green blocks as a part of commercial graphite production, most of the coal tar binders are vaporised and are generally burned in an incinerator to prevent release into the atmosphere, as COV and coal tar can be injurious to health.[20][21]
  • As a main component of the electrode paste used in electric arc furnaces. Coal tar pitch act as the binder for solid filler that can be either coke or calcined anthracite, forming electrode paste, also widely known as Söderberg electrode paste.[22]
  • As a feed stock for higher-value fractions, such as naphtha, creosote and pitch. In the coal gas era, companies distilled coal tar to separate these out, leading to the discovery of many industrial chemicals.

Construction and combustion

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Only half of the coal tar is used for chemical production. The remaining ca. 15M tons are used for bulk applications. For example coal tar is incorporated into some parking-lot sealcoat products used to protect the structural integrity of the underlying pavement.[23] Sealcoat products that are coal-tar based typically contain 20 to 35 percent coal-tar pitch.[23] Research[24] shows that it is used throughout the United States of America, but several areas have banned its use in sealcoat products,[25][26][27] including the District of Columbia; Austin, Texas; Dane County, Wisconsin; the state of Washington; and several municipalities in Minnesota and others.[28][29] From 2025, Canada has also banned its use in sealants.[30]

Coal tar is also used in roofing.

Some coal tar is used as fuel for heating or to fire boilers. Like most heavy oils, it must be heated before it will flow easily.[13]

Medicinal

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Drug precursor

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Coal tar has two minor applications with overlap with medicine. First, some phenolic coal tar derivatives have analgesic (pain-killer) properties. These included acetanilide, phenacetin, and paracetamol aka acetaminophen.[31] Paracetamol may be the only coal-tar derived analgesic still in use today.[32] Industrial phenol is now usually synthesized from crude oil rather than coal tar.[33]

Topical treatments

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Coal tar is used to treat psoriasis and other skin disorders. For this application, coal tar is listed as on the WHO Model List of Essential Medicines.[2][34][35] Medicinally, it is a topical medication applied to skin to treat psoriasis and seborrheic dermatitis (dandruff).[34][35][36] Coal tar is generally available as a generic medication over the counter for topical use, typically as a shampoo.[34][35]

Coal tar may be used in two forms: crude coal tar (Latin: pix carbonis) or a coal tar solution (Latin: liquor picis carbonis, LPC) also known as liquor carbonis detergens.[37][38][39] When used as a topical medication, it is supplied in the form of coal tar 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.

Coal tar is also used as a soap and ointment. It may be applied topically as a treatment for dandruff and psoriasis, and to kill and repel head lice.[34][35][36][40] It may be used in combination with ultraviolet light therapy called Goeckerman therapy.[36][41]

Although coal tar topical products have been used to treat childhood psoriasis, this is an uncommon clinical practice, with risk of cancer development existing from long-term treatment.[41] Coal tar as a monotherapy for childhood psoriasis has not been adequately studied.[41] Other possible adverse effects of using topical coal tar to treat psoriasis include folliculitis, skin irritation, contact dermatitis, phototoxicity, and changes in skin pigmentation and odor.[34]

Safety

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Coal tar derivatives are contra-indicated for people with the inherited red cell blood disorder glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), as they can cause oxidative stress leading to red blood cell breakdown.[42]

Coal tar is a skin irritant.[16]

Side effects include skin irritation, sun sensitivity, allergic reactions, and skin discoloration.[36] It is unclear if use during pregnancy is safe for the baby and its use during breastfeeding is not typically recommended.[43] The exact mechanism of action is unknown.[37] It is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.[2] It exhibits antifungal, anti-inflammatory, anti-itch, and antiparasitic properties.[37]

Cancer

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Many of constituents of coal tar are polycyclic aromatic hydrocarbon, which can be carcinogenic.[44][45][46][47] Long-term, consistent exposure to coal tar likely increases the risk of non-melanoma skin cancers.[48] Evidence is inconclusive as to 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.[49] While coal tar consistently causes cancer in cohorts of workers with chronic occupational exposure, animal models, and mechanistic studies,[14] the data on short-term use as medicine in humans has so far failed to show any consistently significant increase in rates of cancer.[49]

Coal tar contains many polycyclic aromatic hydrocarbons, and it is believed that their metabolites bind to DNA, damaging it.[47] The PAHs found in coal tar and air pollution induce immunosenescence and cytotoxicity in epidermal cells.[50][51] It is possible that the skin can repair itself from this damage after short-term exposure to PAHs but not after long-term exposure.[49] Long-term skin exposure to these compounds can produce "tar warts", which can progress to squamous cell carcinoma.[16]

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.[16] Modern studies have shown that working with coal tar pitch, such as during the paving of roads or when working on roofs, increases the risk of cancer.[14]

The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens, meaning they directly cause cancer.[14][52][53] The U.S. Department of Health and Human Services lists coal tars as known human carcinogens.[54]

In response to public health concerns regarding the carcinogenicity of PAHs some municipalities, such as the city of Milwaukee, have banned the use of common coal tar-based road and driveway sealants, citing concerns of elevated PAH content in groundwater.[55]

Other

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Coal tar causes increased sensitivity to sunlight,[56] 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 13 January 2010 as a substance of very high concern by the European Chemicals Agency.[57]

Regulation

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The U.S. 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 U.S. 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. At levels of 80 mg/m3, coal tar pitch volatiles are immediately dangerous to life and health.[58]

See also

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Additional reading

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References

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  1. ↑ Berenblum I (September 1948). "Liquor picis carbonis; a carcinogenic agent". British Medical Journal. 2 (4577): 601. doi:10.1136/bmj.2.4577.601. PMC 2091540. PMID 18882998.
  2. 1 2 3 "ToxFAQs for Creosote". US Centers for Disease Control and Prevention. 8 July 2024. Retrieved 21 September 2025.
  3. ↑ Vallee Y (1998). Gas Phase Reactions in Organic Synthesis. CRC Press. p. 107. ISBN 978-90-5699-081-7.
  4. ↑ Hornbostel C (1991). Construction Materials: Types, Uses and Applications. John Wiley & Sons. p. 864. ISBN 978-0-471-85145-5. Archived from the original on 18 September 2017.
  5. 1 2 Blümer GP, Collin G, Höke H (2011). "Tar and Pitch". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a26_091.pub2. ISBN 978-3-527-30673-2.
  6. ↑ "History The Early Years (1863–1881)". Bayer AG. Retrieved 4 February 2021.
  7. ↑ "Dyes from Coal Tar Products". Scientific American. 20 February 2024. Retrieved 9 July 2025.
  8. ↑ Sneader W (2005). Drug Discovery: A History. John Wiley & Sons. p. 356. ISBN 978-0-471-89979-2. Archived from the original on 18 September 2017.
  9. ↑ "Coal Tar Oil | OEC".
  10. ↑ Ronalds BF (2019). "Bonnington Chemical Works (1822-1878): Pioneer Coal Tar Company". International Journal for the History of Engineering & Technology. 89 (1–2): 73–91. doi:10.1080/17581206.2020.1787807. S2CID 221115202.
  11. ↑ Smith M. "GANSG – Coal Tar Distillers". Igg.org.uk. Archived from the original on 19 June 2013. Retrieved 8 March 2013.
  12. ↑ Granda M, Blanco C, Alvarez P, Patrick JW, Menéndez R (2014). "Chemicals from Coal Coking". Chemical Reviews. 114 (3): 1608–1636. Bibcode:2014ChRv..114.1608G. doi:10.1021/cr400256y. hdl:10261/202957. PMID 24080106.
  13. 1 2 Speight JG (2015). "Coal gasification processes for synthetic liquid fuel production". In Luque R, Speight JG (eds.). Gasification for Synthetic Fuel Production. Woodhead Publishing Series in Energy. Woodhead. pp. 201–220 (212). doi:10.1016/B978-0-85709-802-3.00009-6. ISBN 978-0-85709-802-3.
  14. 1 2 3 4 Coal-tar pitch (PDF). IARC. Archived (PDF) from the original on 21 May 2016. Retrieved 10 June 2017. it was concluded that there is sufficient evidence in humans for the carcinogenicity of occupational exposures during paving and roofing with coal tar pitch. ... Six coal-tar pitches and three extracts of coal-tar pitches all produced skin tumours, including carcinomas, when applied to the skin of mice
  15. ↑ Betts WD (1997). "Tar and pitch". In John Wiley & Sons, Inc (ed.). Kirk-Othmer Encyclopedia of Chemical Technology (5th ed.). New York: John Wiley & Sons, Inc. doi:10.1002/0471238961. ISBN 978-0-471-23896-6.
  16. 1 2 3 4 5 Roberts L (2014). "Coal Tar". In Wexler P (ed.). Encyclopedia of Toxicology (Third ed.). Oxford: Academic Press. pp. 993–995. doi:10.1016/b978-0-12-386454-3.00012-9. ISBN 978-0-12-386455-0. composition of coal tar will be influenced by the process used for pyrolytic distillation as well as by the original composition of the coal ... He then demonstrated excess cancers occurring in laboratory animals when coal tar is applied to the ears and skin ... [therapeutic effect] is thought to involve decreased epidermal proliferation ... Coal tar is classified as a human carcinogen ... Both inhalation and dermal routes of exposure are considered hazardous.
  17. ↑ Granda M, Blanco C, Alvarez P, Patrick JW, Menéndez R (2014). "Chemicals from Coal Coking". Chemical Reviews. 114 (3): 1608–1636. Bibcode:2014ChRv..114.1608G. doi:10.1021/cr400256y. hdl:10261/202957. PMID 24080106.
  18. ↑ Hathaway AW (2011). Remediation of Former Manufactured Gas Plants and Other Coal-Tar Sites. Taylor & Francis Group.
  19. ↑ "Market Study: Carbon Black". Ceresana. Retrieved 26 April 2013.
  20. ↑ "CDC - Immediately Dangerous to Life or Health Concentrations (IDLH): Coal tar pitch volatiles - NIOSH Publications and Products". www.cdc.gov. 2 November 2018. Retrieved 5 October 2021.
  21. ↑ Speight JG (2015). Asphalt materials science and technology. Amsterdam: Elsevier Science. p. 60. ISBN 978-0-12-800501-9. OCLC 922698102.
  22. ↑ Beukes JP, Roos H, Shoko L, Van Zyl PG, Neomagus HW, Strydom CA, et al. (June 2013). "The use of thermomechanical analysis to characterise Söderberg electrode paste raw materials". Minerals Engineering. 46–47: 167–176. Bibcode:2013MiEng..46..167B. doi:10.1016/j.mineng.2013.04.016. ISSN 0892-6875.
  23. 1 2 Mahler BJ, Van Metre PC (2 February 2011). "Coal-Tar-Based Pavement Sealcoat, Polycyclic Aromatic Hydrocarbons (PAHs), and Environmental Health". U.S. Geological Survey Fact Sheet. Archived from the original on 28 March 2013. Retrieved 8 March 2013.
  24. ↑ Van Metre PC, Mahler BJ (December 2010). "Contribution of PAHs from coal-tar pavement sealcoat and other sources to 40 U.S. lakes". The Science of the Total Environment. 409 (2): 334–344. Bibcode:2010ScTEn.409..334V. doi:10.1016/j.scitotenv.2010.08.014. PMID 21112613.
  25. ↑ "City of Austin Ordinance 20051117-070" (PDF). 17 November 2005. Archived (PDF) from the original on 31 May 2013. Retrieved 8 March 2013.
  26. ↑ "District Bans Coal-Tar Pavement Products". 26 June 2009. Archived from the original on 26 December 2012. Retrieved 8 March 2013.
  27. ↑ "Ordinance 80 : Establishing Regulations on Coal Tar Sealcoat Products Application and Sale" (PDF). Dane County Office of Lakes and Watersheds. 1 July 2007. Archived (PDF) from the original on 24 August 2011. Retrieved 8 March 2013.
  28. ↑ "Coal Tar Free America – Bans". Archived from the original on 6 October 2014. Retrieved 8 March 2013.
  29. ↑ Mahler BJ (14 April 2011). Causes of Increasing Concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) in U.S. Lakes (PDF). PAHs Increasing in Urban U.S. Lakes. Environmental and Energy Study Institute. Archived from the original (PDF) on 5 October 2011. Retrieved 8 March 2013.
  30. ↑ "Compliance guide for the Certain Products Containing Toxic Substances Regulations". Government of Canada. 25 November 2025.
  31. ↑ Dronsfield A (1 July 2005). "Pain relief: from coal tar to paracetamol". Education in Chemistry. Vol. 42, no. 4. Royal Society of Chemistry. pp. 102–105. Archived from the original on 13 October 2017. Retrieved 14 June 2018.
  32. ↑ Brown T, Dronsfield A, Ellis P (1 July 2005). "Pain relief: from coal tar to paracetamol". Royal Society of Chemistry.
  33. ↑ Jones AW (June 2011). "Early drug discovery and the rise of pharmaceutical chemistry". Drug Testing and Analysis. 3 (6): 337–344. doi:10.1002/dta.301. PMID 21698778.
  34. 1 2 3 4 5 "Psoriasis treatment: Coal tar". American Association of Dermatology. 2025. Retrieved 21 September 2025.
  35. 1 2 3 4 Chat VS, Kearns DG, Uppal SK, Han G, Wu JJ (August 2022). "Management of Psoriasis With Topicals: Applying the 2020 AAD-NPF Guidelines of Care to Clinical Practice". Cutis. 110 (2 Suppl): 8–14. doi:10.12788/cutis.0573. PMID 36219602.
  36. 1 2 3 4 Stuart MC, Kouimtzi M, Hill SR, eds. (2009). WHO Model Formulary 2008 (PDF). World Health Organization. pp. 306–308. hdl:10665/44053. ISBN 978-92-4-154765-9.
  37. 1 2 3 Maibach HI (2011). Evidence Based Dermatology. PMPH-USA. pp. 935–936. ISBN 978-1-60795-039-4. Archived from the original on 18 September 2017.
  38. ↑ Hughes J, Donnelly R, James-Chatgilaou G (2001). Clinical pharmacy : a practical approach - Society of Hospital Pharmacists of Australia. South Yarra: Macmillan Publishers Australia. p. 114. ISBN 978-0-7329-8029-0.
  39. ↑ Paghdal KV, Schwartz RA (August 2009). "Topical tar: back to the future". Journal of the American Academy of Dermatology. 61 (2): 294–302. doi:10.1016/j.jaad.2008.11.024. PMID 19185953.
  40. ↑ "Scalp psoriasis". National Psoriasis Foundation. 2025. Retrieved 21 September 2025.
  41. 1 2 3 Lie E, Choi M, Wang SP, Eichenfield LF (January 2024). "Topical Management of Pediatric Psoriasis: A Review of New Developments and Existing Therapies". Paediatric Drugs. 26 (1): 9–18. doi:10.1007/s40272-023-00592-9. PMC 10769900. PMID 37847480.
  42. ↑ US EPA National Center for Environmental Assessment (15 March 2009). "Hematologic Disorders". hero.epa.gov. Retrieved 21 April 2020.
  43. ↑ "Coal Tar use while Breastfeeding | Drugs.com". www.drugs.com. Archived from the original on 18 January 2017. Retrieved 13 January 2017.
  44. ↑ Creosote. US: Agency for Toxic Substances Disease Registry, Division of Toxicology, Dept. of Health and Human Services, Public Health Service. 2002. OCLC 816079578.
  45. ↑ "Public Health Statement for Creosote". Agency for Toxic Substances and Disease Registry. September 2002.
  46. ↑ "EUR-Lex - 32013R1272 - EN - EUR-Lex". eur-lex.europa.eu. Archived from the original on 19 October 2015. Retrieved 10 June 2017. ...are classified as carcinogens of category 1B in accordance with Annex VI to Regulation (EC) No 1272/2008 of the European Parliament
  47. 1 2 "COAL TAR - National Library of Medicine HSDB Database". toxnet.nlm.nih.gov. Archived from the original on 28 May 2017. Retrieved 10 June 2017.
  48. ↑ Moustafa GA, Xanthopoulou E, Riza E, Linos A (August 2015). "Skin disease after occupational dermal exposure to coal tar: a review of the scientific literature". International Journal of Dermatology. 54 (8): 868–879. doi:10.1111/ijd.12903. PMID 26183242. S2CID 205189697.
  49. 1 2 3 Roelofzen JH, Aben KK, Oldenhof UT, Coenraads PJ, Alkemade HA, van de Kerkhof PC, et al. (April 2010). "No increased risk of cancer after coal tar treatment in patients with psoriasis or eczema". The Journal of Investigative Dermatology. 130 (4): 953–961. doi:10.1038/jid.2009.389. hdl:11370/94bb85e0-0bc8-4648-86a2-3f9c8e264886. PMID 20016499.
  50. ↑ Pan TL, Wang PW, Aljuffali IA, Huang CT, Lee CW, Fang JY (April 2015). "The impact of urban particulate pollution on skin barrier function and the subsequent drug absorption". Journal of Dermatological Science. 78 (1): 51–60. doi:10.1016/j.jdermsci.2015.01.011. PMID 25680853.
  51. ↑ Qiao Y, Li Q, Du HY, Wang QW, Huang Y, Liu W (July 2017). "Airborne polycyclic aromatic hydrocarbons trigger human skin cells aging through aryl hydrocarbon receptor". Biochemical and Biophysical Research Communications. 488 (3): 445–452. Bibcode:2017BBRC..488..445Q. doi:10.1016/j.bbrc.2017.04.160. PMID 28526404.
  52. ↑ IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. (2012). "Chemical Agents and Related Occupations.". Coal-Tar Pitch. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Lyon (FR): International Agency for Research on Cancer.
  53. ↑ "COAL-TARS (Group I)" (PDF). IARC MONOGRAPHS SUPPLEMENT 7. IARC. 1987. p. 175. ISBN 978-92-832-1411-3. Archived (PDF) from the original on 15 March 2016. Evidence for carcinogenicity to humans (sufficient)
  54. ↑ "Report on Carcinogens, Fourteenth Edition: Coal Tars and Coal-Tar Pitches" (PDF). National Toxicology Program, Department of Health and Human Services. Archived (PDF) from the original on 1 February 2017. Retrieved 10 June 2017.
  55. ↑ Quirmbach C (7 February 2017). "Milwaukee Common Council Bans Coal Tar Sealants". Wisconsin Public Radio.
  56. ↑ "Sun-Sensitive Drugs (Photosensitivity to Drugs)". MedicineNet. WebMD. 22 August 2008. p. 5. Archived from the original on 17 March 2013. Retrieved 8 March 2013.
  57. ↑ "Candidate List of substances of very high concern for Authorisation". echa.europa.eu/home. nd. Retrieved 27 October 2021.
  58. ↑ "CDC – NIOSH Pocket Guide to Chemical Hazards – Coal tar pitch volatiles". cdc.gov. Archived from the original on 8 December 2015. Retrieved 27 November 2015.
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