Papular urticaria and insect bite reactions

Firm, dome-shaped, oedematous pink papules with a central punctum, often with a surrounding weal, sometimes blistering centrally. New crops appear while old ones are still fading.

The surrounding erythema and the pink weal fade from view, so the lesion presents as a firm palpable papule - and papules remain palpable across the Fitzpatrick range, so feel the skin rather than relying on seeing redness. Side-lighting shows the dome shape well. The more important point is what comes after: post-inflammatory hyperpigmentation is the dominant and most distressing feature of this condition in brown and black skin, routinely outlasting the itch by many months and frequently the reason the family attends at all. The child may present with dozens of dark macules on the shins, long after the bites that caused them, and these are sometimes mistaken for a primary pigmentary disorder, for bruising or for neglect. Pigment lability of this kind in darker skin is well described in general paediatric dermatology, and it is why bite prevention matters more here, not less - every bite leaves a mark that will last.

• Grouped, clustered or linear lesions on exposed skin - the distribution betrays the cause
• Intensely itchy, with excoriation and often secondary impetiginisation
• A central punctum where it can be seen
• Recurrent crops over seasons, with old and new lesions coexisting
• Often only one child in a household reacts - sensitisation is individual, so the absence of bites in siblings does not exclude it
• Blistering (bullous) reactions are common on the legs and alarm families disproportionately

• Chickenpox (varicella) — The commonest misdiagnosis. Both show crops at different stages, but chickenpox is centripetal, febrile, mucosal and over in two weeks; papular urticaria is on exposed skin, afebrile and recurs for seasons
• Scabies, including crusted scabies — Also intensely itchy papules; scabies has burrows, affects finger webs, wrists and genitals, and - crucially - affects contacts too
• Acute urticaria — True weals come and go within 24 hours each; these papules persist for days to weeks and leave marks
• Benign mechanical petechiae — Resolving bite marks on the shins are often read as bruises and raise safeguarding questions; the history, distribution and central punctum usually resolve it
• Pityriasis lichenoides, including PLEVA — Also recurring crops of papules in a well child, but crusted, eroding and scarring rather than urticarial
• Molluscum contagiosum — Also papular, but pearly and umbilicated, not itchy at first, and without a seasonal or clustered pattern

1. Name the pattern out loud - grouped lesions on exposed skin with a central punctum. Families have usually been told this is chickenpox, an allergy or a skin infection
2. Address the source rather than only the skin: pets and flea treatment, bedding and bedbugs, and outdoor exposure. Without that the child simply returns
3. Treat the itch - a potent-enough topical corticosteroid for a short course on lesional skin, and a sedating antihistamine at night if sleep is disrupted. Emphasise that scratching is what causes the infection and the scarring
4. Treat secondary bacterial infection where it is present, not prophylactically
5. Warn about the pigmentary tail, especially in darker skin. The dark marks will persist for months after the itch has gone and are not active disease. Say it before they return for it
6. Advise insect repellent and covering exposed skin, and explain that this is prevention of marks as much as of itch
7. Be alert that this cuts both ways. Resolving bite marks on a child's legs can trigger a safeguarding referral, so document the distribution, the central punctum and the history clearly, and the next clinician inherits the explanation rather than the alarm. But do not let a bite explanation retire the question: marks that are not bites, bruising in a non-mobile baby, an inconsistent or changing history, or injury elsewhere all still go down the safeguarding route (NICE CG89; NG76 on child abuse and neglect). `nappy-rash` and `neonatal-rashes` carry the same both-ways framing - this entry is the third corner of it

Discharge with symptomatic treatment, source advice and GP follow-up. This condition recurs, so the family needs a plan rather than a single prescription.

• Singh S, Mann BK. Insect bite reactions. Indian J Dermatol Venereol Leprol 2013;79(2):151-64
• Laude TA. Approach to dermatologic disorders in black children. Semin Dermatol 1995;14(1):15-20 - pigment lability
• NICE CG89 - Child maltreatment: when to suspect maltreatment in under 18s - cited for the bruising and injury patterns that warrant suspicion
• NICE NG76 - Child abuse and neglect: recognising, assessing and responding