Coal tar shampoo does not cause permanent hair loss. There is no clinical evidence linking coal tar, at the concentrations found in over-the-counter shampoos, to follicle damage or lasting thinning. However, coal tar can dry out hair and make it brittle, which may lead to breakage that looks and feels like hair loss. In many cases, the hair loss people notice while using coal tar shampoo is actually caused by the scalp condition they’re treating, not the treatment itself.
Why Hair Might Seem Thinner During Treatment
Coal tar shampoo is most commonly used for scalp psoriasis, seborrheic dermatitis, and stubborn dandruff. All three conditions involve scalp inflammation, and inflammation itself is a well-documented trigger for hair shedding. Psoriasis patients with scalp involvement frequently report hair loss, but the cause in most cases is the inflammatory process combined with physical trauma from scratching itchy lesions. The hair loss from scalp psoriasis is almost always reversible, with complete regrowth once the inflammation resolves.
So if you started a coal tar shampoo and noticed more hair falling out, there’s a good chance the shedding was already underway before you began treatment. The timing creates a false association: you started a new product and your hair thinned, so the product gets the blame.
How Coal Tar Can Affect Hair Quality
Coal tar can cause irritation in some people and may leave hair dry and brittle. Brittle hair snaps more easily, and if breakage is widespread, it can make hair appear thinner overall. This is hair breakage, not hair loss from the root. The difference matters: breakage shortens existing strands, while true hair loss means the follicle stops producing new hair. Breakage reverses once you stop or reduce exposure.
Coal tar also temporarily discolors blond, bleached, or color-treated hair. This cosmetic effect has nothing to do with hair health, but it can make hair look duller or feel rougher, adding to the impression that something is wrong.
Animal studies show that coal tar applied to skin increases epidermal thickness and can cause comedone formation (clogged pores) and shrinkage of oil-producing glands. The hair follicle appears to be a major route through which coal tar penetrates skin. While clogged follicles could theoretically contribute to temporary shedding, this has not been demonstrated as a meaningful cause of hair loss in humans using standard shampoo concentrations.
What Coal Tar Actually Does on Your Scalp
The exact mechanism of coal tar isn’t fully understood, but it appears to slow down the rapid skin cell turnover that causes flaking and scaling. In conditions like psoriasis, skin cells multiply far too quickly. Coal tar suppresses this overproduction, helping the scalp return to a more normal cycle. It also has anti-inflammatory and itch-relieving properties, which is why it remains a go-to treatment for inflamed, flaky scalps despite being one of the oldest topical therapies still in use.
The FDA classifies coal tar as Category I, meaning safe and effective, for treating dandruff, seborrheic dermatitis, and psoriasis. Over-the-counter products are approved at concentrations between 0.5 and 5 percent. Most shampoos fall well within this range and are intended for use about twice per week.
When Coal Tar Could Be a Problem
Some people are more sensitive to coal tar than others. If the product causes persistent redness, burning, or increased irritation on your scalp, that inflammatory response could worsen hair shedding rather than help it. This doesn’t mean coal tar is inherently dangerous for hair. It means the product isn’t right for your scalp. Switching to a lower concentration or a different active ingredient (like salicylic acid or zinc pyrithione) is a reasonable next step.
Overuse can also contribute to problems. Using coal tar shampoo daily when it’s designed for twice-weekly application increases the chance of drying out both your scalp and hair. Sticking to the recommended frequency and leaving the product on your scalp for only the directed amount of time reduces the risk of irritation and brittleness.
Separating Hair Loss From Hair Breakage
If you’re concerned about thinning while using coal tar shampoo, look at where the hair is coming from. Hair that falls out from the root will have a small white bulb at one end. That signals shedding, which is most likely related to your underlying scalp condition. Short, broken pieces without a bulb suggest breakage from dryness or brittleness, which the shampoo could be contributing to.
In either case, the effect is temporary. Hair lost to inflammatory shedding regrows once the scalp condition is controlled. Hair that breaks off from dryness recovers once the drying agent is removed or used less frequently. Neither scenario involves permanent follicle damage at standard over-the-counter concentrations.