What is pityriasis versicolor and what causes it?

Pityriasis versicolor is a rash caused by a yeast-like germ called malassezia (also called pityrosporum). Small numbers of this germ commonly live on the skin, and do no harm. However, some people are prone to this germ multiplying on their skin more than usual, which then leads to a rash developing. Often the germ multiplies and causes the rash for no apparent reason. In some cases, hot, sunny or humid weather seems to trigger the germ to multiply on the skin.

Pityriasis versicolor is fairly common. It affects around one in twenty adults at some point in their life. Pityriasis versicolor is sometimes called tinea versicolor.

What are the symptoms?

The rash usually starts as small pale patches. At first these usually appear on the chest, neck, or upper arms. The rash sometimes spreads to the abdomen, thighs, and back. More patches may appear, and patches next to each other may join together. The affected skin may become slightly scaly.

The rash is usually pale, and is barely noticeable if you are fair-skinned. You may not notice it until after you sunbathe. Affected areas do not tan, and therefore the rash becomes more obvious on tanned skin. The pale patches are more obvious if you have dark skin. (Sometimes the rash is darker than the skin in fair-skinned people, and it looks like brown marks.)

There are usually no other symptoms. Sometimes it is slightly itchy.

Pictures of pityriasis versicolor can be found here: www.dermis.net/dermisroot/en/15962/diagnose.htm

Is it serious?

No. If you wanted an even suntan, then this rash is a nuisance as pale patches on tanned skin may look unsightly.

Is it infectious or contagious?

No. The yeast-like germ that causes the rash is commonly found on the skin, and usually does no harm. For reasons that are not clear, it seems that the germ multiplies more easily to cause a rash on certain people.

What is the treatment for pityriasis versicolor?

The type of treatment varies between cases and may depend on the location of the rash and also if you have had this condition before. The following are treatment options:

• Ketoconazole shampoo (2%) is commonly advised. You can buy this at pharmacies and it is also available on prescription. Ketoconazole kills the germ that causes this rash. Apply the shampoo neat to affected areas, and then wash off after five minutes. Repeat each day for five days. Some doctors advise that you should then apply the shampoo about once a week for six months to try to clear the skin completely of the germ.
• Selenium sulphide shampoo is an alternative treatment. It is not strictly licensed for the treatment of this rash, but it works. You can buy it from pharmacies or it is also available on prescription. Dilute the shampoo with water 50:50 (half water, half shampoo). Then apply the diluted shampoo to the affected areas and leave to dry for at least 30 minutes or overnight. This should be applied 2-7 times over a fortnight and the course repeated if necessary.
• An antifungal cream is an alternative. You can buy this at pharmacies and they are also available on prescription. (Yeasts are similar to fungal germs and antifungal creams also kill yeasts.) However, these are less commonly recommended if a large area of your skin is affected.
• Antifungal tablets may be prescribed if the rash is over a large area of your skin, or is not cleared by the above treatments.

How can I prevent the rash from coming back?

Some people seem prone to this yeast-like germ multiplying on their skin and the rash may recur after treatment. One option is to apply one of the above shampoos to your skin every 2-4 weeks. This may keep the germ away, or prevent the numbers building up, which will prevent the rash from recurring.

References

• Burkhart CG, Gottwald L, Burkhart CN; Pityriasis versicolor, eMedicine, April 2010.