Coal tar slows the rapid skin cell growth that drives psoriasis plaques. In psoriasis, skin cells multiply roughly ten times faster than normal, piling up into thick, scaly patches. Coal tar works against this process in several ways: it suppresses DNA synthesis in skin cells, reduces inflammation, and relieves itching. These combined effects make it one of the oldest and still widely used topical treatments for psoriasis, available over the counter in concentrations between 0.5% and 5%.
How Coal Tar Slows Skin Cell Buildup
The core problem in psoriasis is that skin cells (keratinocytes) divide too quickly and don’t mature properly. Instead of shedding normally, they stack up on the skin’s surface as raised, flaky plaques. Coal tar addresses this in two ways. First, it suppresses DNA synthesis inside these cells, which directly slows their rate of division. Second, it helps correct the abnormal maturation process, pushing keratinocytes toward more normal development so they’re less likely to accumulate.
Coal tar also has anti-inflammatory properties that calm the redness and swelling around plaques, along with antipruritic (itch-relieving) effects. The itching in psoriasis can be one of the most disruptive symptoms, and coal tar’s ability to address it alongside the visible scaling is part of why the treatment has persisted for over a century despite newer alternatives. It also has mild antimicrobial activity, which can help when cracked or broken plaques are vulnerable to infection.
What the Evidence Shows
Coal tar has a strong track record in clinical use. In one contralateral study of 45 patients (where one side of the body received coal tar and the other a topical steroid), a coal tar gel was significantly more effective than the corticosteroid after four weeks of treatment. That result may surprise people who assume steroids are always the stronger option.
The most dramatic evidence comes from the Goeckerman regimen, a treatment protocol first published in 1925 that combines crude coal tar with ultraviolet B (UVB) light therapy. Coal tar makes skin more responsive to UV light, and the two treatments amplify each other’s effects. In a study at the University of California San Francisco, 100% of the 25 patients on this regimen achieved a 75% improvement in their psoriasis severity within three months. A larger study of 300 patients found that every single participant achieved 90% or greater clearing of their baseline plaques. These are remarkable response rates, even compared to modern biologic drugs.
Available Forms and How to Use Them
Coal tar comes in shampoos, creams, ointments, gels, foams, and bath solutions. Over-the-counter products in the United States contain between 0.5% and 5% coal tar, which the FDA considers safe and effective for psoriasis. Prescription formulations can contain higher concentrations, sometimes using crude coal tar rather than the refined versions found in drugstore products.
How long you leave it on matters. For scalp psoriasis, coal tar products are typically massaged into the scalp and left for one to two hours before washing off. Coal tar shampoos require less contact time, usually five to ten minutes before rinsing. For body plaques, creams and ointments are applied directly to affected areas. Some people use coal tar at night, covering treated skin with clothing or wraps to maximize contact time and protect bedding from staining.
Side Effects to Expect
Coal tar is messy. It stains clothing, bedding, and light-colored hair. It has a strong, distinctive smell that many people find unpleasant. These cosmetic drawbacks are the main reason some people abandon the treatment despite its effectiveness.
Beyond the mess, coal tar can cause several skin reactions. The most common is photosensitivity: treated skin becomes more sensitive to sunlight, which increases the risk of sunburn. This is actually the same property that makes it effective in combination with UV therapy, but it means you need to protect treated areas from sun exposure for at least 24 hours after application. Other possible reactions include folliculitis (inflamed hair follicles that look like small red bumps), irritation or burning, allergic contact dermatitis, and temporary darkening of the skin in treated areas.
The Cancer Question
Coal tar contains compounds that are known carcinogens in occupational settings. Workers exposed to coal tar and coal-tar pitch on the job have increased rates of skin, lung, bladder, kidney, and digestive tract cancers. This has understandably raised concerns about therapeutic use, and California requires cancer warning labels on OTC coal tar products containing more than 0.5%.
However, the FDA’s position is that there is no scientific evidence that the coal tar in OTC psoriasis products, at concentrations between 0.5% and 5%, is carcinogenic. The distinction comes down to dose and duration: occupational exposure involves far higher concentrations over much longer periods than applying a cream to a few patches of skin. Long-term studies of psoriasis patients using coal tar therapeutically have not shown a meaningful increase in cancer risk. The National Psoriasis Foundation considers OTC coal tar products safe for regular use.
Who Benefits Most From Coal Tar
Coal tar works best for mild to moderate plaque psoriasis and scalp psoriasis. It’s particularly useful for people who want to avoid long-term steroid use, since coal tar doesn’t cause the skin thinning that comes with prolonged corticosteroid application. It’s also a good option for hard-to-treat areas where other topicals may be impractical.
For moderate to severe psoriasis, coal tar is most effective when combined with UV light therapy rather than used alone. The Goeckerman regimen requires daily clinic visits (typically for several weeks), which limits its practicality, but some dermatology centers still offer it as an alternative to systemic medications for patients who prefer to avoid immunosuppressive drugs. For people with mild disease, an over-the-counter coal tar shampoo or cream applied consistently is often enough to keep plaques manageable.