Review of the mechanism of action of coal tar in psoriasis

Purpose: Crude coal tar and its derivatives have been used in modern medicine for the treatment of psoriasis since at least 1925 as part of the Goeckerman regimen. To this day, coal tar remains a safe and highly effective option for the treatment of psoriasis vulgaris. However, the mechanism by which coal tar has its therapeutic effect is unknown. This review summarizes current knowledge of the mechanism by which coal tar has its therapeutic effect in the treatment of psoriasis vulgaris. Material and methods: A Pubmed search was conducted on March 13, 2017 for relevant English language journal articles on the subject and were relevant journal articles were included in this review. Results: Crude coal tar consists of thousands of ingredients, many of which are unidentified. Of these ingredients, the most research has gone into analyzing polycyclic aryl hydrocarbons. These hydrocarbons are thought to be the most likely component of crude coal tar that leads to its effects in psoriasis. Of the aryl hydrocarbons, carbazole has been the most well studied in psoriasis and is hypothesized as being responsible for the treatment efficacy of crude coal tar. Conclusions: Polycyclic aryl hydrocarbons, and specifically carbazole, are thought to be the mechanism by which crude coal tar has its effect in psoriasis. However, further research is warranted to fully characterize the mechanism of action of crude coal tar, with the potential to create new therapies for psoriasis.