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Pityriasis versicolor

What are the aims of this leaflet?

This leaflet has been written to help you understand more about pityriasis versicolor.  It tells you what it is, what causes it, what can be done about it, and where you can find out more about it.

What is pityriasis versicolor?

This rather awkward name gives some idea of what pityriasis versicolor looks like and how it behaves (pityriasis means a type of fine skin scaling, and versicolor means changing colour).  It is a common and harmless rash due to the overgrowth of yeasts that live on everyone’s skin.  These yeasts are not related to yeasts in food or to those that cause thrush.

What causes it?

Large numbers of tiny harmless organisms are present on the surface of everyone’s skin.  They are known as ‘the resident flora’.  They live there, doing no harm. Some of them are yeasts. When the conditions are right, these yeasts can multiply out of control and cause the rash known as pityriasis versicolor. This happens most often in warm moist climates.

Once the rash has come up, its main feature is the way it varies in colour – hence the name versicolor.  It looks fawn or pinkish on an untanned white skin; but sunlight causes the yeasts to make chemicals that upset the pigment cells (melanocytes) in the skin.   As a result the rash fails to tan and so stays paler than the surrounding skin.

The condition is most common in people in their early 20s, and in those who sweat a lot.  It is not catching because we all have these yeasts on our skin even if we do not have the rash of pityriasis versicolor.  It is not clear why some people tend to get it and others do not.

Is it hereditary?

No.

What are its symptoms?

The rash can be mildly itchy but usually causes no trouble apart from its appearance. It often goes unnoticed if only a few patches are present.

What does it look like?

The rash comes up more often on the trunk than on the limbs.  Flat slightly scaly areas of altered colour show up against a background of normal skin.  The colour of the patches ranges from being darker than the surrounding skin (reddish-fawn or brown) in areas that have never seen the sun, to areas that have become pale or whitish after being in the sun.  The darker the skin, the easier it is to see these pale areas.

How will it be diagnosed?

Usually the diagnosis is easy for your doctor to make just by looking at the rash.  The main problem lies in telling a treated, but still pale, area of pityriasis versicolor from vitiligo (which has larger, whiter areas, crops up more often on the face and limbs, and is often permanent).  A dermatologist may shine an ultra-violet (Wood’s) light on the skin to check for the typical yellow fluorescence of pityriasis versicolor.  If there is any doubt, skin scrapings can be looked at under the microscope to see if yeasts are present.

Can it be cured?

Yes: the rash clears with treatment though the pale areas will take a few months to get back to their normal colour.  Pityriasis versicolor does not leave scars.  Sometimes the rash does come back, mainly in the summer, as the yeasts that cause it live on normal skin and never go away completely. 

How can it be treated?

Treatments applied to the skin

Most patients are treated only with applications to the skin. Treatments that destroy the yeasts include ketoconazole and selenium sulphide. They are often used in shampoo form, as they can then cover large areas more easily than creams. How you use them will depend on which type your doctor recommends.  One simple way is to apply the shampoo to wet skin and leave it on for 10 minutes; the treatment has to be repeated daily for 10 days.

Medicines taken by mouth

These include itraconazole.  They work well but are usually kept in reserve for widespread rashes, or those that have not got better with treatment put on the skin. 

Recurrences

The rash of pityriasis versicolor often comes back. Using a medicated shampoo to the trunk from time to time over several months cuts down this risk.  For limited areas of recurrence, ketoconazole or clotrimazole cream can be applied twice daily.  Remember that the pale areas left after treatment may take several months to get back to their normal colour.  This cannot be speeded up.

What can I do?

If you tend to suffer from pityriasis versicolor, and are going on holiday to the sun, you might try using an anti-yeast shampoo to your skin for a few weeks before you go.  Diet plays no part in pityriasis versicolor. 

Where can I get more information about it?

Web links to detailed leaflet:

• www.emedicine.com/derm/topic423.htm
• www.aadassociation.org/Guidelines/superpityriasis.htm