Coal Tar Products for Psoriasis

Is it safe to use coal tar products?

Dermatology consultation woman
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Coal tar products for psoriasis have been around for more than a century. Coal tar is the leftover by-product of coal processing and distillation. There are thousands of compounds in coal tar, and only a fraction of these are identified. For this reason, it is unlikely that coal tar would be approved by the U.S. Food and Drug Administration (FDA) is presented for new drug status.

In any case, coal tar is grandfathered in, having been a medication for longer than the FDA has existed.

Before corticosteroids were first recognized or synthesized for use in inflammatory skin diseases, coal tar was there to help ease the itch. Coal tar preparations appear to exert their anti-psoriasis benefits by interfering with DNA and thus slowing down skin cell growth and turnover. The long-term result is thinning of the psoriatic plaques.

How Is Coal Tar Used?

Coal tar is found in dozens of over-the-counter (OTC) psoriasis and dandruff shampoos, as well as creams, gels, and bath additives. Compound pharmacists can mix crude coal tar (a black, thick paste) or coal tar solution (a 20 percent alcohol-based liquid) with all sorts of bases, including steroid creams and ointments. One effective remedy for hand and foot psoriasis is a compound of steroid with 5 percent coal tar solution and 2 percent salicylic acid, which a pharmacist can mix up with a prescription from your doctor.

Coal tar is often used along with phototherapy, as it sensitizes the skin to ultraviolet radiation.

Care should be taken in avoiding excess sun exposure when using coal tar shampoos and other preparations.

Is Coal Tar Dangerous?

With many unknown ingredients, the question is not too easy to answer definitively. However, 5 percent or greater coal tar is classified as a carcinogen (cancer-causing agent) by the World Health Organization's International Agency for Research on Cancer.

In this regard, it is in the same category as methoxsalen (used in PUVA therapy for psoriasis) and solar radiation, two other forms of psoriasis treatment. Alcoholic beverages and tobacco also qualify in this category.

There are not too many over-the-counter products that carry the full 5 percent crude coal tar concentration considered carcinogenic by the WHO. However, California law is much more strict in this regard and considers even 0.5 coal tar dangerous enough to require a warning on a product's label.

The FDA, in contrast, considers 0.5 to 5 percent OTC coal tar preparations safe for psoriasis, and there is really no evidence linking these weaker preparations to an increased risk of cancer. Although coal tar compounds have been found in the urine of users of an experimental tar-based shampoo, the concentration of coal tar used was around 100 times greater than that of common OTC shampoos.

Studies have been done to see whether coal tar raises the risk of cancer. One study found no increased risk of bladder cancer when used for skin disease. Another large study of people with psoriasis and eczema found no increased risk of skin cancer or non-skin malignancies.

Still Useful in Many Regards

For the most part, worries about coal tar are probably overblown.

Coal tar has several merits, including very low cost and absence of steroids (and, therefore, steroid-related side effects). Typically it is left on for about two hours and rinsed off. This short contact type of therapy helps to prevent staining of clothing and fabrics often seen with the use of coal tar.

Sources

Over-the-Counter (OTC) Topicals. National Psoriasis Foundation. https://www.psoriasis.org/about-psoriasis/treatments/topicals/over-the-counter

Roelofzen JH, Aben KK, Kerkhof PCVD, Valk PGVD, Kiemeney LA. Dermatological exposure to coal tar and bladder cancer risk: A case-control study. Urologic Oncology: Seminars and Original Investigations. 2015;33(1). doi:10.1016/j.urolonc.2013.12.006.

Roelofzen JH, Aben KK, Oldenhof UT, et al. No Increased Risk of Cancer after Coal Tar Treatment in Patients with Psoriasis or Eczema. Journal of Investigative Dermatology. 2010;130(4):953-961. doi:10.1038/jid.2009.389.

Zeichner JA. Use of Topical Coal Tar Foam for the Treatment of Psoriasis in Difficult-to-treat Areas. The Journal of Clinical and Aesthetic Dermatology. 2010;3(9):37-40.

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