Tar – or coal tar – is a by-product of oil production. It is a nearly black viscous liquid or semi-solid that is FDA approved for use in over-the-counter skin and hair care products at concentrations of between 0.5% and 5%.

Coal tar works by slowing the rapid growth of skin cells, reducing inflammation and itching and scaling, so it is often used to treat psoriasis, dandruff and seborrheic dermatitis. Because products containing tar vary quite a bit, and some products may irritate your skin, or cause it to turn red and become dry, it’s a good idea to test them on a small area of your skin.

The FDA requires that any product containing coal tar for over-the-counter use carries appropriate warnings, as it is increases skin sensitivity to sunlight. The FDA also requires the labels of these products to warn that they should not be used for prolonged periods without consulting a doctor. Because tar increases your skin’s sensitivity to sunlight, and can remain active for up to 24 hours, it is important to protect yourself using sunscreen and appropriate clothing, if you are going out in the sun. Also, tar can stain clothing, bed linen and light-colored hair.

Topical formulations of coal tar are available in a variety of preparations, some of the branded products include Balnetar, Betatar Gel, Coal Tar, Cutar, Denorex, Denorex Dry Scalp, Denorex Extra Strength, Denorex Medicated Shampoo and Conditioner, DHS Tar Shampoo, Doak Tar, Doak Tar Oil, Elta Tar, Fototar, G-TAR, Ionil T, Ionil T Plus, MG 217 Psoriasis, MG217 Medicated Tar, Neutrogena T/Derm, Neutrogena T/Gel, Neutrogena T/Gel Extra Strength, Oxipor VHC, PC Tar, Pentrax, Pentrax Gold, Polytar, Psoriasin, Psorigel, T/Gel Conditioner, Tegrin Medicated, Tegrin Medicated Soap, Therapeutic, Theraplex T, Zeta.