Pityriasis alba

Faintly pink or simply pale, poorly demarcated round or oval patches with a fine powdery scale. Often barely noticeable, and sometimes only apparent after sun exposure tans the surrounding skin.

This is a condition whose entire clinical significance changes with skin tone. On pale skin the patches are easily overlooked; on brown and black skin the same hypopigmented patches are conspicuous, and they are a common reason for a family to seek help and a common source of distress and stigma. The appearance differs while the incidence does not - a pattern described for pityriasis alba specifically in general paediatric skin-of-colour literature. Two consequences for the consultation. First, do not minimise it. Telling a family with brown or black skin that this is trivial because it is trivial on white skin is the wrong answer, and it is how trust is lost. Second, be precise that it is hypopigmentation and not depigmentation - pigment is reduced, not absent - because the fear in the room is almost always vitiligo, and that distinction is the reassurance. Post-inflammatory hypopigmentation of this kind is more prominent in skin of colour and resolves slowly, over months to years.

• Poorly defined edges - this is the single most useful discriminator from vitiligo, which is sharply bordered
• Fine, dry, powdery scale over the patch
• Pigment reduced but not absent - examine under good light, and the patch is lighter than surrounding skin rather than chalk-white
• Associated with atopic skin: dryness, a history of eczema, asthma or hay fever
• More noticeable in summer, when the surrounding skin darkens and the patch does not
• Asymptomatic or mildly itchy

• Vitiligo — The fear in the room. Vitiligo is sharply demarcated and completely depigmented - chalk or milk white - with no scale. Pityriasis alba is ill-defined, scaly and retains pigment
• Pityriasis versicolor — Also hypopigmented and scaly, but on the trunk and shoulders rather than the face, with a more defined edge and a positive mycology
• Atopic eczema and infected eczema — Not so much a mimic as the parent condition - pityriasis alba is a sign of atopic skin and should prompt you to look for and treat eczema elsewhere
• Tinea corporis, cruris and pedis — Also scaly and round, but with an active raised edge and central clearing, and it spreads
• Lichen striatus — The hypopigmented form is also a pale patch in a child, but linear and following Blaschko lines

1. Confirm the edges are ill-defined and that pigment is reduced rather than absent - that examination is the whole consultation
2. Name vitiligo and exclude it out loud. The family is thinking it even if they have not said it, and leaving it unaddressed means they go home still frightened
3. Treat the underlying dry atopic skin: regular emollient, and a short course of a mild topical corticosteroid if there is active eczema
4. Advise sun protection, which reduces the contrast as the surrounding skin tans rather than treating the patch itself
5. Give an honest timescale: months, sometimes a year or more. Repigmentation is slow, and a family expecting weeks will return repeatedly
6. Do not prescribe an antifungal, which is the common wrong treatment

Discharge with emollient advice and an explanation. GP follow-up if the underlying eczema needs managing. No investigation is needed in a typical case.

• Tay YK, Kong KH, Khoo L, Goh CL, Giam YC. The prevalence and descriptive epidemiology of atopic dermatitis in Singapore school children. Br J Dermatol 2002;146(1):101-6 - pityriasis alba in 25% of 12,323 children examined
• Rao M, Young K, Jackson-Cowan L, Kourosh A, Theodosakis N. Post-inflammatory hypopigmentation: review of the etiology, clinical manifestations, and treatment options. J Clin Med 2023;12(3):1243 - more prominent in skin of colour, with cosmetic and psychosocial consequences
• Laude TA. Approach to dermatologic disorders in black children. Semin Dermatol 1995;14(1):15-20 - pityriasis alba among the disorders that vary in appearance rather than in incidence