Coal Tar for Psoriasis

What is psoriasis?

Psoriasis is a common skin condition which commonly develops as patches of red, scaly skin. There is no 'once and for all' cure. Treatment aims to clear the rash as much as possible. However, as psoriasis tends to come and go, you may need courses of treatment on and off throughout your life. There are various treatments. There is no 'best buy' that suits everybody. The treatment advised by your doctor may depend on the severity, location and type of psoriasis. Also, one treatment may work well in one person, but not in another.

This leaflet is just about coal tar in the treatment of psoriasis. There are separate leaflets on psoriasis in general, and on the other common topical treatments for psoriasis - vitamin D analogues, dithranol, steroid creams and tazarotene.

What is coal tar?

Coal tar is thick brown or black liquid. It is a by-product when coal is carbonized to make coke or gasified to make coal gas. Coal tar contains many different chemicals. Creams and ointments that contain coal tar have been used to treat psoriasis for many years. It is not clear how coal tar works. It may reduce the turnover of the skin cells. It also seems to reduce inflammation and have 'antiscaling' properties.

Some notes about coal tar and psoriasis

Follow the instructions carefully that come with the preparation you are prescribed. Also, do persevere with the treatment as it often takes several weeks for improvement to occur in the skin. The following are some general points that aim to complement - not to replace - the instructions that come with the preparation that you are prescribed.

Crude coal tar is the most effective form, typically in a concentration of 1 to 10% in a soft paraffin base. However, it is messy and smelly to use, so few people tolerate it. It was mainly used in hospital skin departments, but is less commonly used these days.

Modern creams that contain coal tar are more pleasant and are suitable for home use. Modern creams typically contain between 0.4% and 2% crude coal tar. There are many brands and types. Your doctor may prescribe one. It is common to start with a mild strength and increase to a stronger strength if needed. It is common to apply twice daily - but follow the instructions that you are given.

As a rule, do not use coal tar creams on flexures (the skin creases such as the front of elbows, behind knees, groins, armpits, etc). Also, avoid using on the face and getting it in the eyes. However, the milder creams can be used on the face and flexures - your doctor will advise. Do not use on broken or inflamed skin.

Some coal tar preparations may stain skin, hair, clothes and fabrics. Therefore, as a precaution you may wish to wear old clothes and use old bed linen when you first start using coal tar to see if this happens with your preparation.

Contact of coal tar products with normal skin is not normally harmful. Therefore, coal tar creams can be used liberally and can be used for both large plaques (patches) of psoriasis, and for widespread small patches. However, in some people coal tar can cause skin irritation, a contact allergy, or an acne-like rash. These are temporary and clear if the cream is stopped. Some coal tar preparations are used to add to bath water which can also be helpful for widespread psoriasis.

Tar based shampoos which have a coal tar content of up to 2.5% are popular for treating scalp psoriasis.

Are coal tar preparations safe?

Coal tar has been used for many years to treat psoriasis and is generally considered a safe treatment. However, some doubt about the safety of coal tar has been raised. It may possibly be a risk factor in the cause of some skin cancers. For example, it is known that occupational exposure to coal tar increases the risk of developing skin cancer. As a precaution, in Germany, cosmetic manufacturers have voluntarily agreed to ban coal tar from their shampoos.

Also, experimental studies have shown that some chemicals in coal tar shampoos that are carcinogenic (polycyclic aromatic hydrocarbons) can get into the body in small quantities. The significance of this is not known.

Despite the above, there is no firm evidence to say that medical tar products used to treat psoriasis cause skin cancer, or any other type of cancer or disease, or have an effect on a growing baby in a pregnant woman. Therefore, they continue to be used to treat psoriasis. However, as a precaution, pregnant women may wish to avoid their use.

Combination treatments

A coal tar preparation is sometimes used in combination with another treatment for psoriasis if either treatment alone is not sufficient. For example, a coal tar preparation can be used together with UVB light therapy (which is another treatment sometimes used for psoriasis). This can be an effective method of clearing mild psoriasis. Another example is that some doctors sometimes recommend a treatment plan for a few weeks when a steroid cream is used in the daytime, with a coal tar cream used at bedtime.

Further sources of information

Psoriasis Association

Dick Coles House, 2 Queensbridge, Bedford Road, Northampton NN4 7BF
Tel (helpline): 0845 6 760 076 Web: www.psoriasis-association.org.uk