Pityriasis alba

Definition

Pityriasis alba is a mild form of eczema that occurs mainly in children and often accompanies atopic dermatitis. The name describes its appearance: "pityriasis" refers to the fine scale, "alba" to the pale colour (hypopigmentation).

Occurrence & epidemiology

It is common worldwide, with a prevalence in children of around 5%. Children and adolescents aged 3 to 16 years are mainly affected, boys and girls equally. In dark skin the hypopigmentation is more noticeable and the condition is probably more common.

Aetiopathogenesis

The cause is unknown. Dry skin and atopic dermatitis often coexist. Sun exposure makes the patches more visible because the surrounding skin tans. Other proposed factors such as trace element deficiency or Malassezia yeasts are unproven.

Clinical features

• Usually 1–20 round, oval or irregular patches or thin plaques of 0.5–5 cm, mostly poorly defined.
• Mainly on the cheeks and chin, also on the neck, shoulders and upper arms; little or no itch.
• Typical sequence: slightly scaly pink patch → hypopigmented patch with fine scale → scale-free post-inflammatory hypopigmentation → resolution.
• Hypopigmentation is more noticeable in summer, dryness and scaling in winter. Patches clear after about a year on average and skin colour returns completely to normal; recurrences occur.

Diagnosis

• Clinical.
• Wood lamp: no enhancement of the hypopigmentation, no fluorescence.
• Mycology (microscopy, culture) negative.
• Dermoscopy: poorly defined pale area, white structureless areas, faint pigment network, fine white scale, normally pigmented hairs.
• Biopsy rarely needed: mild spongiotic dermatitis, reduced melanin.

Differential diagnoses

• Atopic dermatitis (atopic eczema)
• Tinea faciei
• Vitiligo
• Pityriasis versicolor (tinea versicolor)
• Seborrhoeic dermatitis
• Hypomelanosis of Ito (incontinentia pigmenti achromians)
• Pityriasis rosea

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References (selection)

1. DermNet: Pityriasis alba
2. PubMed: Pityriasis Alba--Common Disease, Enigmatic Entity: Up-to-Date Review of the Literature (PMID 26477326)
3. PubMed: Pityriasis alba revisited: perspectives on an enigmatic disorder of childhood (PMID 21416771)

Cross-references