The Health Benefits of Coal Tar

Century-Old Remedy Used for Psoriasis and Seborrheic Dermatitis

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Dermatology consultation woman
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Coal tar is a by-product of coal processing that has been used for more than a century to treat skin problems. Today, it is considered an effective, safe, and inexpensive topical treatment for psoriasis and seborrheic dermatitis (dandruff). Available in different strengths and formulations, coal tar is included on the World Health Organization's List of Essential Medicines and approved for use by the U.S. Food and Drug Administration (FDA) under the classification "generally recognized as safe and effective" (GRASE).

Health Benefits

Coal tar belongs to a class of drugs called keratoplastics that also includes benzoyl peroxide, tretinoin, and salicylic acid. It works by directly interfering with DNA synthesis in skin cells. With psoriasis, a disease characterized by the hyperproduction of skin cells, this action help normalize skin cell production and decrease the size of psoriatic plaques.

Coal tar also promotes the shedding of dead cells from the top layer of skin, called the stratum corneum. This can help reduce dandruff as well as the itchiness and scaling associated with plaque psoriasis. Coal tar is especially useful in treating scalp psoriasis and hard-to-treat palmoplantar psoriasis (psoriasis of the palms and soles).

A 2014 study in Indian Journal of Dermatology reported that a 12-week course coal tar combined with salicylic acid was just as effective in relieving chronic plaque psoriasis as the prescription drugs calcipotriol and betamethasone.

Possible Side Effects

Over-the-counter (OTC) coal tar products are considered safe if used in concentrations of between 0.5% and 5%. With that being said, coal tar can sometimes irritate and dry the skin, particularly at higher strengths. This can often be mitigated by applying a moisturizer before the coal tar preparation.

Coal tar can also make the skin more sensitive to sunlight for up to 24 hours after application. To avoid sunburn, wash your skin thoroughly after using a coal tar product and apply a high-SPF sunscreen if you plan to be out in the sun.

Coal tar can also stain clothes, towels, bed linen, and even light-colored hair. It often helps to apply the preparation in the shower, washing or rinsing off thoroughly to avoid accidentally staining. Any discoloration of the hair is usually temporary and will resolve after a few shampoos. Newer liquor carbonis distillate (LCD) coal tar products are less likely to stain naturally light or color-processed hair.

While there are compounds in coal tar considered carcinogenic (cancer-causing), the level of these in a 0.5% to 5% preparation is considered negligible.

According to the FDA, there was no evidence that "the risk of cancer is greater in consumers who regularly use OTC drug products containing coal tar than in consumers who do not."

There are also no known drug interactions associated with coal tar preparations. Allergic reactions are rare but may occur. If you are prone to allergies, patch test a product on a small area of skin and to wait 24 hours to see if you develop a rash or irritation of any sort.

Dosage and Preparation

Coal tar is found in a plethora of 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.

The dosage varies by the strength of the preparation. To avoid side effects, follow the instructions on the package label or ask your pharmacist or dermatologist for advice. Topical products should be massaged into the skin and allowed to dry. Those intended for baths or foot soaks should be thoroughly mixed and used for 10 to 15 minutes. Take extra care when using coal tar in bathtubs or showers as it can make surfaces extremely slippery.

Coal tar is intended for use on the skin only. Take special care when applying to face, avoiding the eyes, nose, and mouth. The same applies to the rectum and genitals. If you accidentally get coal tar in your eyes or mucosal tissues, rinse thoroughly with cool water for 15 minutes.

Coal tar preparations should never be applied to inflamed, broken, or infected skin. Only use coal tar in children under the direction of a dermatologist.

Coal tar is sometimes used alongside phototherapy as it sensitizes the skin to ultraviolet (UV) radiation. This should only be performed by a dermatologist who is trained to deliver the correct UV dose using specialized equipment that emits narrow-band ultraviolet light B (UVB) radiation.

Never use a tanning bed or lamp to treat psoriasis as this will almost invariably do more harm than good.

What to Look For

There are literally hundreds of different coal tar preparations found on drugstore shelves and in online stores. When choosing a product, opt for those that have undergone testing with an independent certifying body like the U.S. Pharmacopeia (USP), NSF International, or ConsumerLab. In this way, you will know that the product contains the ingredients listed on the label in the declared potency and amounts.

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