Pityriasis Alba
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Direct answer
Pityriasis alba is a common, self-limiting condition of ill-defined, hypopigmented, lightly scaling patches, mostly on the face of children and young adults. It is thought to be a mild eczema-related or post-inflammatory process, and it is more visible in darker skin. The patches resolve over months, and treatment with emollients, sun protection and short courses of mild topical steroids is usually sufficient.
What you must remember
- Morphology: ill-defined, hypopigmented, slightly scaly patches, most often on the cheeks, with occasional lesions on the upper arms.
- Population: children and young adults, often with atopy or dry skin, and more noticeable in darker skin types.
- Pathogenesis: the exact cause is uncertain, but the condition is linked to mild atopic dermatitis or to post-inflammatory change.
- Sun effect: sun exposure tans the surrounding normal skin, so the pale patches become more conspicuous in summer.
- Differential diagnosis: vitiligo, which has sharp borders and no scale, tinea versicolor, which has fine scale and a positive potassium hydroxide test, and post-inflammatory hypopigmentation.
- Wood's lamp: accentuates vitiligo strongly, whereas pityriasis alba shows little accentuation.
- Natural history: benign, with resolution over months to years, sometimes leaving residual pallor.
- Treatment: emollients, daily sunscreen and short courses of mild topical corticosteroid, with topical calcineurin inhibitors as an option on the face.
Pityriasis alba against its commonest mimics
Pityriasis alba is most often confused with vitiligo and pityriasis versicolor, and the table separates the three on the features exam stems usually describe.
| Feature | Pityriasis alba | Vitiligo | Pityriasis versicolor |
|---|---|---|---|
| Border | Ill-defined | Sharply demarcated | Variable, often ill-defined |
| Scale | Fine and light | None | Fine, branny scale |
| Wood's lamp | Little accentuation | Bright white | Yellow-green fluorescence |
| Key test | Clinical diagnosis | Clinical; histology shows absent melanocytes | Potassium hydroxide preparation |
Ill-defined patches with fine scale on the face of an atopic child favour pityriasis alba. Sharply bordered white patches without scale suggest vitiligo, and a potassium hydroxide preparation confirms pityriasis versicolor when scale and fluorescence are present. Prolonged steroid use should be avoided until the differential is settled, because facial skin atrophies easily.
Most children also have mild dry skin elsewhere on the body, which supports an eczema-related cause and justifies a daily emollient for the whole body. Families often worry about vitiligo, so clear reassurance that the condition is benign and usually fades with time is an important part of the consultation.
Where the exam tries to catch you
Pityriasis alba questions test the differential diagnosis, the steroid trap and the role of sun protection.
- Trap: diagnosing vitiligo in every hypopigmented child on the face Correct: pityriasis alba is ill-defined, scaly and self-limiting, whereas vitiligo is sharply demarcated and depigmented.
- Trap: prescribing long courses of potent steroids for facial patches Correct: mild steroids in short courses are used, because facial skin atrophies easily.
- Trap: assuming the patches are contagious or need antifungal therapy Correct: pityriasis alba is non-infectious, and antifungals are needed only when a potassium hydroxide test confirms pityriasis versicolor.
- Trap: ignoring sun protection Correct: sun exposure darkens the surrounding skin and makes the patches more visible, so sunscreen is part of management.
Frequently asked questions
Is pityriasis alba a form of vitiligo?
Pityriasis alba is not a form of vitiligo. It is a separate, self-limiting condition of ill-defined hypopigmented patches with fine scale. Vitiligo has sharply demarcated depigmented patches without scale and needs its own management.
Which investigation distinguishes pityriasis alba from pityriasis versicolor?
A potassium hydroxide preparation of scale from pityriasis versicolor shows fungal hyphae and spores. Wood's lamp examination may show yellow-green fluorescence in pityriasis versicolor. Pityriasis alba shows neither finding, which is the key distinction in exam questions.
What is the treatment for facial pityriasis alba?
Emollients, sun protection and short courses of a mild topical corticosteroid are the usual treatment for facial pityriasis alba. Topical calcineurin inhibitors are an option where steroid atrophy is a concern. Most lesions resolve over months even without specific treatment.
Why does pityriasis alba become more visible in summer?
Pityriasis alba becomes more visible in summer because sun exposure tans the surrounding normal skin while the affected patches stay pale. This contrast makes the lesions more noticeable. Daily sunscreen reduces the contrast and forms part of management.