Coal tar therapy has been used for more than a century in dermatology. It is a topical (applied to the skin) treatment mostly used for acute (short-term) scalp psoriasis. It has anti-inflammatory and anti-scaling properties that are useful in treating chronic plaque psoriasis. Crude coal tar (coal tar BP, a standard formulation) is the most effective form, typically in a concentration of 1% to 10% in a soft paraffin base, although few people with psoriasis can tolerate the smell and mess.
Cleaner extracts of coal tar included in brand-named products are more practicable for home use, but they are less effective and improvement takes longer.
Contact of coal tar products with normal skin is not usually harmful and they can be used for widespread small lesions; however, irritation, contact allergy, and sterile folliculitis (pusfilled spots at the base of the hair) can occur. The milder tar extracts can be used on the face and skin folds. Tar baths and tar shampoos are also helpful and some of these products can be purchased over the counter without a prescription.
Coal tar has also been used in combination with ultraviolet B light in hospitals. It was formulated by American dermatologist William Goeckerman in 1925 and is known as the Goeckerman method. Some hospital day-units still use tar products in the bath prior to treatment.
Tar based products include: