What is psoriasis?
Psoriasis is a common condition where there is inflammation of the skin. It typically develops as patches (plaques) of red, scaly skin. Once you develop psoriasis it tends to come and go throughout life. A flare-up can occur at any time. The frequency of flare-ups varies. There may be times when psoriasis clears for long spells. However, in some people the flare-ups occur often. Also, the severity of psoriasis varies greatly. In some people it is mild with a few small patches that develop and are barely noticeable. In others, there are many patches of varying size. In many people the severity is somewhere between these two extremes.
There is no once-and-for-all cure for psoriasis. 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 available for psoriasis. There is no best treatment that suits everybody. The treatment advised by your doctor may depend on the severity, location and type of psoriasis that you have. Also, one treatment may work well in one person, but not in another.
What is coal tar?
Coal tar is thick brown or black liquid. It is a by-product when coal is carbonised to make coke or gasified to make coal gas. Coal tar contains many different chemicals. It has been used for many years to treat psoriasis. Now, creams, ointments, lotions, pastes, scalp treatments, bath additives and shampoos that contain coal tar are available.
It is not clear how coal tar works. It may reduce the turnover of skin cells. It also seems to reduce inflammation and have anti-scaling properties.
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, branded creams and other treatments 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.
Tar-based shampoos which have a coal tar content of up to 2.5% are popular for treating scalp psoriasis.
This leaflet is just about coal tar used to treat psoriasis. The following are some general points that aim to complement (not to replace) the instructions that come with the preparation that you are prescribed. There is a separate leaflet, ‘Psoriasis’, that discusses psoriasis in general. See also separate leaflets discussing some other common treatments for psoriasis, called ‘Dithranol & Psoriasis – Short Contact’ and ‘Vitamin D Analogues for Psoriasis’.
How do you use coal tar treatments for psoriasis?
There are many brands and types of coal tar preparations available. Your doctor may prescribe one. Follow the instructions that come with the preparation you are prescribed carefully. Also, do persevere with the treatment, as it often takes several weeks for improvement of your psoriasis. It may take 6 to 12 weeks for improvement in some people.
It is common to start with a mild-strength treatment and to increase to a stronger strength if needed. Often, coal tar creams, ointments or pastes should be applied to psoriasis plaques once or twice daily – but follow the instructions that you are given. Some shampoos or scalp applications should only be used once a week. Your doctor will advise how you should use the preparation that you are given. Coal tar preparations that can be added to bath water may be helpful for widespread psoriasis.
As a rule, do not use coal tar creams or other coal tar treatments on flexures (the skin creases such as the front of elbows, behind knees, groins, armpits, etc). Also, avoid using them on your face, as you need to be careful not to get them into your eyes. However, some of the milder creams can be used on your face and flexures – your doctor will advise. Your doctor will also advise you on whether it is safe for you to use coal tar treatments on your genital areas.
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 bedlinen 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 product is stopped.
You should be careful to avoid exposure to sunlight if you are using a coal tar treatment. This is because it may make your skin react to the sunlight, causing a rash. If you do go out in the sun, cover up with clothing and use a sunblock cream or lotion.
Are coal tar preparations safe?
Coal tar preparations have been used for over a hundred years to treat psoriasis. However, coal tar does contain some substances that are recognised carcinogens (substances that may potentially cause cancer). So, over time, some doubt about the safety of coal tar has been raised, including the possibility that its use may lead to an increased risk of some cancers. Supporting this, some studies have shown an increased risk of cancer in animals exposed to coal tar or in people who work with coal tar.
However, the results of a large study involving over 13,000 people who have used coal tar preparations to treat psoriasis or eczema were published recently. The study did not find any link between the use of preparations containing coal tar and an increased risk of cancer (including skin cancer and other cancers).
Is there anyone who should not use coal tar treatments?
You should not use coal tar to treat psoriasis if:
- Your skin is broken or very inflamed.
- Your skin is infected.
- You have pustular psoriasis.
- Your psoriasis has come on acutely (suddenly).
It is advised that pregnant women should not use coal tar treatments during the first three months of pregnancy. However, they are thought to be safe to use later in your pregnancy. You can use coal tar treatments while you are breast-feeding.
Coal tar is often combined with another treatment for psoriasis, such as a steroid or salicylic acid, so that both can be given together in the same preparation.
Also, 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 ultraviolet B (UVB) light therapy (which is another treatment sometimes used for psoriasis). Another example is that some doctors may recommend a treatment plan for a few weeks where a steroid cream is used in the daytime and a coal tar cream used at bedtime.
Further sources of information
Dick Coles House, 2 Queensbridge, Northampton, NN4 7BF
Tel (helpline): 0845 676 0076
Founded in 1968, the Association has three fundamental aims: to support those who have psoriasis; to raise awareness about psoriasis; to fund research into the causes of and treatments for psoriasis.
PAPAA – The Psoriasis and Psoriatic Arthritis Alliance
PO Box 111, St Albans, Hertfordshire, AL2 3JQ
Tel: 01923 672837
Provides support and information for people with psoriasis and psoriatic arthritis.
References and Disclaimer | Provide feedback
- Psoriasis, Prodigy (May 2010)
- Diagnosis and management of psoriasis and psoriatic arthritis in adults, Scottish Intercollegiate Guidelines Network – SIGN (October 2010)
- Psoriasis – General Management, British Association of Dermatologists (BAD), 2008
- Lui H et al, Plaque Psoriasis, Medscape, Mar 2011
- British National Formulary
- Roelofzen JH, Aben KK, Oldenhof UT, et al; No increased risk of cancer after coal tar treatment in patients with psoriasis J Invest Dermatol. 2010 Apr;130(4):953-61. Epub 2009 Dec 17. [abstract]