Dermatitis

Pityriasis alba

Created 2008.

Learning objectives

  • Identify and manage pityriasis alba

Clinical features

Pityriasis alba is a common skin disorder in children (90%) and young adults. It is particularly prevalent in atopics. It is characterised by one or more flaky pink patches and hypopigmentation. The patches are often found on the cheeks and upper arms and are more noticeable in darker skinned children. It is generally asymptomatic.

The cause of pityriasis alba is unknown but is thought to be a type of dermatitis. The dry component may appear more obvious in winter months. The hypopigmentation is more obvious in summer because of relative tanning of unaffected skin.

After some weeks or months the dry surface resolves leaving a smooth pale patch, which slowly disppears over a year or so.

Pityriasis alba

Differential diagnosis

The differential diagnosis of pale dry patches on the face or limb of a child includes:

  • Postinflammatory hypopigmentation, in which there is a history of another inflammatory skin disorder;
  • Atopic dermatitis, characterised by very itchy symmetrical plaques that respond to topical steroids;
  • Psoriasis, in which there are symmetrical scaly plaques in typical sites including scalp;
  • Seborrhoeic dermatitis, which is uncommon in children aged 2-12;
  • Pityriasis versicolor, which affects upper trunk of adolescents and adults and has positive microscopy;
  • Tinea corporis, which also has positive mycology and there is often a history of contact with a kitten;
  • Nummular dermatitis, in which there are dry or crusted itchy round patches;
  • Naevus depigmentosus, a stable pale mark present since birth;
  • Vitiligo, in which there are progressive macules with complete pigment loss and no scale most often arising around eyes or mouth:
  • Hypopigmented mycosis fungoides (rare), in which there are persistent progressive infiltrated plaques.

Investigations

Mycology is negative in pityriasis alba, but may be necessary to rule out a dermatophyte infection or pityriasis versicolor.

Skin biopsy is rarely necessary and may be reported as nonspecific dermatitis.

Treatment

No specific treatment is necessary in most children as the patches are asymptomatic and resolve by themselves.

A trial of mild topical steroid cream is sometimes warranted for a couple of weeks. It can be expected to reduce the redness, scaling and itch (if present). Long term, a moisturiser may prove as effective.

Sunscreens may be useful to reduce tanning of surrounding skin.

Activity

Assess the prevalence of pityriasis alba in a paediatric population.

See smartphone apps to check your skin.
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Related information

References:

On DermNet NZ:

Information for patients

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Books about skin diseases:

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