Coal tar is used primarily as a skin treatment for psoriasis, dandruff, and seborrheic dermatitis, but it also has significant industrial applications in roofing, road paving, and electrode manufacturing. It’s a thick, dark liquid produced when coal is heated in the absence of air, and humans have applied it to skin conditions for well over a century. Its medical use was first specifically documented in 1894, though tar-based remedies for skin problems date back nearly 2,000 years.
Treating Psoriasis
Coal tar’s most well-known use is treating plaque psoriasis, the most common form of the disease. It works by slowing down the rapid overgrowth of skin cells that causes the thick, scaly patches characteristic of psoriasis. The exact mechanism isn’t fully understood, but coal tar appears to suppress DNA activity in skin cells, which reduces how fast they multiply. It also helps normalize the way those skin cells mature, correcting a key defect in psoriatic skin. On top of that, it has anti-inflammatory and anti-itch properties, making it useful for both the visible plaques and the discomfort that comes with them.
The American Academy of Dermatology lists coal tar as effective for plaque psoriasis, scalp psoriasis (especially when itching is the main complaint), stubborn psoriasis on the palms and soles, and general scaling. It comes in shampoos, ointments, foams, and bath solutions. For scalp psoriasis, a coal tar shampoo needs to contact the scalp directly, not just sit on the hair.
A more intensive approach called the Goeckerman regimen combines coal tar with ultraviolet B (UVB) light therapy. First published in 1925, this treatment takes advantage of the fact that coal tar makes skin more sensitive to UV light, boosting the effectiveness of phototherapy. The combination works better than UV light alone. Patients typically undergo 20 to 30 sessions, each lasting at least four hours, with coal tar applied under plastic wrap before being washed off with mineral oil and soap. The regimen was originally a round-the-clock inpatient treatment but now runs in outpatient day-care settings, five days a week until the psoriasis clears.
Dandruff and Seborrheic Dermatitis
Coal tar shampoos are also used to manage dandruff and seborrheic dermatitis, a condition that causes flaky, red, irritated skin on the scalp. In a clinical trial of 163 people with seborrheic dermatitis or dandruff, a coal tar shampoo significantly reduced both flaking and redness after 29 days compared to a placebo shampoo. Dandruff scores dropped more sharply with coal tar, and clinician-rated redness improved roughly twice as much as with the placebo. While coal tar shampoos are less commonly used today than newer options like ketoconazole, they remain an effective over-the-counter choice.
OTC Products and Concentrations
In the United States, the FDA allows coal tar at concentrations of 0.5 to 5 percent in over-the-counter products marketed for dandruff, seborrheic dermatitis, or psoriasis. Products must list both the coal tar source used and the final concentration of coal tar in the product. You’ll find coal tar in several forms: medicated shampoos for scalp conditions, ointments and creams for body plaques, foams for hard-to-reach areas, and liquid solutions designed to be added to a bath.
Side Effects and Practical Drawbacks
Coal tar is effective, but it comes with some inconveniences that make many people hesitant to use it. The most noticeable is staining. Coal tar can discolor skin, clothing, bedding, and light-colored or dyed hair. Skin staining fades after you stop using the product, but fabric stains are harder to manage.
Mild stinging is common, particularly with gel and liquid formulations. Skin irritation and rash are possible but rare. The more important concern is sun sensitivity: after applying coal tar, you should protect the treated skin from direct sunlight and avoid tanning beds for at least 72 hours. Coal tar acts as a photosensitizer, meaning it amplifies your skin’s reaction to UV radiation. This is the same property that makes it useful in combination light therapy, but it can cause a severe sunburn-like reaction if you’re not careful.
Cancer Risk
Coal tars are classified as known human carcinogens by the National Toxicology Program, based on extensive evidence from occupational studies. Workers exposed to coal tar and coal tar pitch in industrial settings, including coal-briquette workers, roofers, and electrical trades workers, have elevated rates of skin cancer, lung cancer, bladder cancer, and digestive tract cancers. There have also been case reports of skin cancer among patients using therapeutic coal tar preparations.
That said, the concentrations in medical products (0.5 to 5 percent) are far lower than those encountered in occupational settings, and short-term or intermittent use for skin conditions carries a different risk profile than years of daily workplace exposure. Animal studies have confirmed that coal tar can increase the chance of skin cancer, which is one reason dermatologists typically recommend it for limited periods rather than as a permanent daily treatment.
Industrial and Construction Uses
Outside of medicine, coal tar pitch (the residue left after distilling coal tar) is widely used in construction and manufacturing. In roofing, solid blocks of coal tar pitch are melted and spread in layers with roofing felt to create waterproof flat roofs. Road paving uses coal tar as a binder mixed with stone chips, either in hot-mix applications or chip sealing. Coal tar pitch is also essential in manufacturing the carbon electrodes used in aluminum smelting.
Pavement Sealants and Environmental Concerns
One of coal tar’s most widespread non-medical uses has been in pavement sealcoat, the black liquid sprayed on parking lots and driveways to protect asphalt. Coal tar-based sealants are a major source of polycyclic aromatic hydrocarbons (PAHs), a group of chemicals that contaminate nearby soil, stormwater, and waterways. These sealants are more common east of the Continental Divide in the U.S., while asphalt-based alternatives dominate in the west.
Growing evidence of environmental harm has led several states, counties, and municipalities to ban coal tar sealants. Austin, Texas, was an early mover, prohibiting their use in 2006. Sediment cores collected from Lady Bird Lake, the city’s primary receiving waterway, showed a 58 percent decrease in PAH concentrations after the ban took effect. That measurable improvement has strengthened the case for similar bans elsewhere.