Creams that contain coal tar have been used to treat psoriasis for many
years. If you use a coal tar preparation, do persevere as it can take
6-12 weeks for an improvement in the skin. A coal tar cream is
sometimes used in combination with other treatments if either treatment
alone is not sufficient. For example, some doctors sometimes recommend
a treatment plan for a few weeks where a steroid cream is used in the
daytime, with coal tar cream used at bedtime.
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
References
© EMIS and PiP 2008 Updated: 21 Feb 2008
