Alternative Names: Coal tar.
Coal tar is a messy and smelly – but effective – topical treatment for various skin conditions. It can also stain clothing and irritate the skin. However, coal tar products that are on the market now are much easier to use than they once were.
Crude coal tar is obtained by the destructive distillation of bituminous coal at very high temperatures. It is believed that over 10,000 different compounds make up coal tar but only a few hundred have been identified. The main groups of compounds making up crude coal tar are 48% hydrocarbons, 42% carbon and 10% water.
In its natural form coal tar is a thick, nearly black, viscous liquid with a characteristic smell. It is most often obtained in solution form (ranging in strength from 0.1 to 20%) and mixed with other ingredients, such as salicylic acid and sulfur, to make lotions, creams, ointments and shampoos.
Crude and refined coal tar preparations should still be available through a pharmacist who will compound any coal tar preparation as prescribed by a doctor.
Exactly how coal tar works to treat various health conditions is not completely understood. It appears to have antimicrobial, antipruritic (reduce itching) and keratoplastic (normalize keratin growth in the skin and reduce scaling) effects.
Coal tar is still used to treat a variety of skin disorders, particularly conditions where the skin is flaky and scaly:
Tips for using coal tar products:
Most patients tolerate coal tar preparations well. It may initially cause mild stinging or skin irritation as your body gets use to the medicine. However, if this continues stop using the preparation and see your doctor.
When used on the scalp, it may temporarily discolor bleached, tinted, light blond or grey hair. Coal tar also stains skin and clothing. The stain on the skin will wear off after you have stopped using the preparation.
Coal tar may cause photosensitivity, hence the need to stay out of direct sunlight when using these preparations. In some instances your doctor may use the Goeckerman regimen, which is a combination of coal tar with UVB phototherapy. This has been found to be particularly successful for treating psoriasis.
There is some controversy over the carcinogenic (cancer-causing) potential of coal tar. In animal studies, it has been shown to increase the chance of skin cancer. However, in human studies using safe doses, an increase in the incidence of cancers has not been found after 75 years of documented use. It's safe to use coal tar if you follow your doctor's instructions.
It has been known for a long time that coal tar (2-5%) helps psoriasis and it is available as crude coal tar coal, tar lotion, and in refined forms incorporated into ready made creams, lotions and shampoos. In general, the more messy and smelly the tar preparation is, the better it is likely to work – so please be prepared to persevere with it.
The use of coal tar is declining as newer compounds effective against the different forms of psoriasis are replacing it. However, it still has the advantages of being low cost and causing less systemic toxicity as compared with more modern therapies.
A chemical similar to those found in tar may be used on its own – known as Dithranol or Anthralin. This must be used cautiously as it can irritate, but a strength and base can usually be found to suit and help the individual person's psoriasis. Tar treatments can lead to steady and effective control. It is usually best to apply a tar or dithranol preparation daily, to be followed later by ultra-violet light treatment.