Coal tar shampoo is a medicated shampoo that slows the rapid growth of skin cells on your scalp, reducing flaking, itching, and redness caused by conditions like psoriasis, seborrheic dermatitis, and stubborn dandruff. It’s available over the counter in most drugstores and is classified by the FDA as a Category I ingredient, meaning it’s considered both safe and effective for these uses.
How Coal Tar Works on Your Scalp
Coal tar is a thick, dark liquid produced when coal is heated in the absence of air. It contains a complex mixture of thousands of organic compounds, including phenols and polycyclic aromatic hydrocarbons. Over 400 individual compounds have been identified in coal tar, and researchers estimate as many as 10,000 may actually be present.
The therapeutic effect comes down to one key action: coal tar suppresses DNA synthesis in skin cells. In conditions like scalp psoriasis, skin cells multiply far too quickly, piling up into thick, flaky patches. Coal tar slows that turnover rate, giving the scalp time to shed cells at a more normal pace. It also reduces the inflammation, swelling, and redness that accompany these conditions. This combination of slowing cell growth and calming irritation is what makes it effective where regular dandruff shampoos sometimes fall short.
Conditions It Treats
Coal tar shampoo is specifically used for three overlapping scalp conditions:
- Dandruff: the mildest form, with visible white or yellowish flakes and mild itching.
- Seborrheic dermatitis: a more inflammatory version of dandruff with red, greasy, scaly patches that can extend beyond the scalp to the face and ears.
- Scalp psoriasis: thick, silvery-white scales over red, raised plaques, often extending past the hairline.
For dandruff alone, coal tar generally works but may not be the strongest option available. A clinical trial comparing a 4% coal tar shampoo against a 2% ketoconazole (antifungal) shampoo found that coal tar on its own appeared less effective than the antifungal for dandruff and seborrheic dermatitis. However, when coal tar was combined with an antifungal agent, the combination matched or even outperformed ketoconazole alone, producing a greater reduction in the area of seborrheic dermatitis by day 29 of treatment. This suggests coal tar works best for dandruff when paired with other active ingredients, while its real standalone strength is in psoriasis, where slowing cell turnover is the primary goal.
Concentrations and Product Strengths
Over-the-counter coal tar shampoos typically contain coal tar solution at concentrations ranging from about 0.5% to 5%. The FDA has reviewed specific formulations, including shampoos with 1.8% coal tar solution for dandruff control. Some products list higher percentages of “coal tar solution” on the label, but the actual concentration of active coal tar compounds is lower because the solution itself is diluted. A product labeled “5% coal tar solution,” for instance, contains significantly less pure coal tar than that number suggests.
Prescription-strength coal tar preparations exist at higher concentrations and in different formats like creams and ointments, but the FDA’s over-the-counter review has focused specifically on shampoo formulations. If your scalp condition isn’t responding to drugstore-strength products, a dermatologist can guide you toward stronger options.
How to Use It
The basic technique matters more than people realize. Wet your hair thoroughly, then massage the shampoo directly into your scalp, not just your hair. The active ingredients need contact with the skin where the problem is. Lather it up and leave it on your scalp for several minutes before rinsing. Then repeat the process a second time. Most product labels recommend using it at least twice a week, though your doctor may suggest a different frequency depending on the severity of your condition.
One common mistake is treating coal tar shampoo like a regular shampoo and rinsing it off immediately. That contact time is essential. The longer the coal tar sits on affected skin (within reason), the more it can suppress the overactive cell production causing your symptoms.
Side Effects and Practical Downsides
Coal tar shampoo has two well-known drawbacks that aren’t medical concerns but drive many people to stop using it: the smell and the staining. Coal tar has a strong, distinctive odor that some people find tolerable and others find unbearable. It can also stain light-colored or blonde hair, giving it a yellowish or brownish tint. Skin that comes in contact with the product can temporarily darken as well, and it readily stains clothing and towels.
To minimize staining, rinse thoroughly and use the shampoo with older towels you don’t mind discoloring. If you have light hair, pay attention to how your hair responds after the first few uses. Some people alternate coal tar shampoo with their regular shampoo to reduce the cosmetic impact.
Coal tar also increases your skin’s sensitivity to ultraviolet light. After using it, your scalp (and any skin it touched) is more vulnerable to sunburn. Wearing a hat or limiting direct sun exposure on treatment days is a practical precaution, especially in summer.
The Cancer Question
Coal tar contains polycyclic aromatic hydrocarbons, some of which are known carcinogens in industrial settings. This understandably raises concern when you see “coal tar” on a shampoo label. The distinction matters: industrial exposure involves high concentrations, prolonged contact, and inhaled fumes over years, while medicated shampoos use low concentrations applied briefly to the skin.
The FDA classifies coal tar at OTC concentrations as safe and effective. Cancer epidemiology studies of patients who have received coal tar therapy in various forms have failed to link treatment with an increased risk of cancer. The Cosmetic Ingredient Review Expert Panel has echoed the FDA’s position that coal tar as an antidandruff drug ingredient is adequately addressed by existing regulations. That said, the panel has noted that using coal tar at the lowest concentration that still works is the sensible approach, and that using it as directed (rather than more frequently or at higher concentrations than recommended) is important.
How It Compares to Other Options
Coal tar shampoo sits in a lineup of medicated shampoos that each tackle scalp conditions through different mechanisms. Antifungal shampoos containing ketoconazole or zinc pyrithione target the yeast that contributes to dandruff and seborrheic dermatitis. Salicylic acid shampoos help loosen and remove existing flakes. Coal tar’s unique role is slowing cell production itself, which makes it particularly suited to psoriasis where the fundamental problem is cells multiplying too fast.
For straightforward dandruff, an antifungal shampoo is often the more effective first choice. For scalp psoriasis, coal tar has decades of clinical use behind it and remains a go-to treatment. Many people with seborrheic dermatitis or psoriasis rotate between different medicated shampoos, using coal tar some days and an antifungal or salicylic acid shampoo on others, to address the condition from multiple angles.