What is pityriasis alba?
Pityriasis alba is a low-grade type of eczema/dermatitis that primarily affects children.
The name refers to its appearance: pityriasis refers to its characteristic fine scale, and alba to its pale colour (hypopigmentation).
Who gets pityriasis alba?
Pityriasis alba is common worldwide with a prevalence in children of around 5%.
- It mainly affects children and adolescents aged 3 to 16 years, but may also arise in older and younger people
- It affects boys and girls equally.
- It is more prominent, and may also be more prevalent, in dark skin compared to white skin.
What causes pityriasis alba?
The cause of pityriasis alba is unknown.
- It often coexists with dry skin and atopic dermatitis.
- It often presents following sun exposure, perhaps because tanning of surrounding skin makes affected areas more prominent.
Researchers have not reached any conclusions about the relationship of pityriasis alba to the following:
- Ultraviolet radiation
- Excessive or inadequate bathing
- Low levels of serum copper
- Malassezia yeasts (which produce a metabolite, pityriacitrin, that inhibits tyrosinase thus causing hypopigmentation)
What are the clinical features of pityriasis alba?
Classic pityriasis alba usually presents with 1 to 20 patches or thin plaques.
- Most lesions occur on the face, especially on cheeks and chin.
- They may also arise on neck, shoulders and upper arm and are uncommon on other sites of the body.
- Size varies from 0.5 to 5 cm in diameter.
- They are round, oval or irregular in shape.
- Pityriasis alba may have well-demarcated or poorly defined edges.
- Itch is minimal or absent.
- Hypopigmentation is more noticeable in summer, especially in dark-skinned children.
- Dryness and scaling is more noticeable in winter, when environmental humidity tends to be lower.
Typically, each area of pityriasis alba goes through several stages.
- Slightly scaly pink plaque with just palpable papular surface
- Hypopigmented plaque with fine surface scale
- Then post-inflammatory hypopigmented macule without scale
Complications of pityriasis alba
None are known.
How is pityriasis alba diagnosed?
Pityriasis alba can be confused with several other disorders that cause hypopigmentation.
To exclude these, investigations may include:
- Wood lamp examination: hypopigmentation does not enhance, and there is no fluorescence in pityriasis alba
- Scrapings for mycology: microscopy and fungal culture are negative in pityriasis alba
- Skin biopsy: biopsy is rarely required, but may reveal mildly spongiotic dermatitis and reduction in melanin
What is the treatment for pityriasis alba?
No treatment is necessary for asymptomatic pityriasis alba.
- A moisturising cream may improve the dry appearance
- A mild topical steroid (hydrocortisone) cream may reduce redness and itch
- Calcineurin inhibitors, pimecrolimus cream and tacrolimus ointment, may be as effective as hydrocortisone and have been reported to speed recovery of skin colour.
How can pityriasis alba be prevented?
The development or prominence of pityriasis alba can be reduced by avoiding exposure to sunlight.
What is the outlook for pityriasis alba?
Pityriasis clears up after a few months, or in some cases persists for up to two or three years. The colour gradually returns completely to normal.