Pityriasis versicolor Dr Trisha Macnair Pityriasis versicolor (also known as tinea alba or tinea versicolor) results in patches of different pigmentation on the skin.

In this article

What causes it? Who's affected?

What are the symptoms? How's it diagnosed?

What's the treatment?

Most adults have the yeast Malassezia furfur (or Pityrosporum orbiculare) growing quite harmlessly on their skin.

Occasionally, this yeast changes into a more invasive form, putting out long filaments known as hyphae into the top layer of dead skin cells (the stratum corneum). This growth rarely does any significant harm. However, sometimes it releases chemicals that interfere with the activity of skin's pigment cells. As a result, changes occur in the pigmentation or colour of the skin.

Pityriasis versicolor isn't contagious - everyone has the yeast on their skin and internal changes allow the fungus to thrive.

Disruption to the skin surface (scratches or eczema, for example) can enable the fungus to penetrate the skin layers. Problems with the immune system may interfere with the skin's ability to keep this at bay and increase the risk of pityriasis versicolor.

Although pityriasis versicolor is harmless, the same yeast can sometimes cause more bothersome skin conditions, such as seborrhoeic dermatitis (cradle cap) and pityrosporum folliculitis (when the yeast infects the hair follicles).

It's not clear what triggers the yeast to change its form, but some risk factors for pityriasis versicolor are known.

The yeast particularly likes warm, fat-rich conditions. Therefore, pityriasis versicolor is more common in tropical and sub-tropical climates.

It's particularly common among teenagers around the time of puberty, when hormonal changes lead to increased production of oily sebum by the skin, although people of any age can be affected.

In some tropical areas, more than 40 per cent of the population have the condition.

The main symptom of pityriasis versicolor is patches of increased or decreased pigmentation on the skin. These patches may be:

• Pale pink, brownish or whitish
• Scaly and slightly raised

However, they're not usually itchy or uncomfortable.

The trunk and arms are most commonly affected, especially the upper back and chest. In children, the face is often affected.

Skin changes may be more obvious in summer. Sunbathing can make the patches less obvious or accentuate them if pigmentation has been lost.

Pityriasis versicolor is often easily recognised by a doctor. However, many other conditions produce a similar rash, so extra tests may be done.

Scrapings of the skin may be sent to a laboratory to check for the yeast. Shining an ultraviolet light on to the rash will make the patches fluoresce a yellow/green colour. This is known as a Wood's light test.

In most cases, pityriasis versicolor is easy to treat. Antifungal skin washes, shampoos, cream or tablets should clear the infection and keep it at bay.

However, changes in pigmentation won't disappear until the damaged layers of skin have been shed and replaced by fresh skin cells. This may take several months.

Occasionally, the condition returns after treatment and more intensive therapy is needed.

This article was last medically reviewed by Dr Rob Hicks in July 2006.