Pityriasis versicolor is a rash caused by a yeast-like bug. It is not harmful. Treatment can clear the rash. Some people who are prone to this condition need regular treatment to prevent the rash from recurring.

What is pityriasis versicolor and what causes it?

Pityriasis versicolor is a rash caused by a yeast-like bug called 'pityrosporum'. Small numbers of this bug commonly live on the skin, and do no harm.

However, some people seem prone to this bug multiplying on their skin more than usual, which leads to a rash. Often the bug multiplies and causes the rash for no apparent reason. In some cases, hot, sunny, or humid weather seems to 'trigger' the bug to multiply on the skin.

What are the symptoms?

The rash usually starts as small pale patches. These usually appear on the chest, neck, or upper arms at first. 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.

Is it serious?

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

Is it infectious or contagious?

No. The yeast-like bug 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 bug multiplies more easily to cause a rash on certain people.

What is the treatment for pityriasis versicolor?

Ketoconazole shampoo (2%) is commonly advised. You can buy this at pharmacies, and it is also available on prescription. Ketoconazole kills the bug that causes this rash. Apply the shampoo 'neat' to affected areas, and then wash off after 5 minutes. Repeat each day for 5 days. Some doctors advise that you should then apply the shampoo about once a week for 6 months to try and clear the skin completely of the bug.
Selenium sulphide shampoo is an alternative. It is not strictly licensed for the treatment of this rash, but it works. You can buy it from pharmacies. Apply the shampoo 'neat' to the affected areas. Leave to dry, and wash off in 24 hours. Apply twice a week for four weeks.
An antifungal cream is an alternative. You can buy these at pharmacies, and they are also available on prescription. (Yeasts are similar to fungus bugs, and antifungal creams also kill yeasts.)
Anti-fungal tablets may be prescribed if the rash is over a large area of your skin, or is not cleared by the above treatments.

Note: after treatment, the colour of the affected skin usually takes 3-6 months to return to normal.

How can I prevent the rash from coming back?

Some people seem prone to this yeast-like bug 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 bug away, or prevent the numbers building up, which will prevent the rash from recurring.

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