“I sent you a photo of his lip — is it catching?”

Herpes labialis is common and self-limiting, but the GP task is to look around the lesion — at the child’s eczema, eyes and hydration, and at who else is in the house. Recurrent HSV-1 typically follows a prodrome of tingling and may be triggered by a cold, fever, sunlight or stress; lesions crust and heal in about 7–10 days. Topical aciclovir offers only a modest benefit if started early, so it is optional; oral antivirals are reserved for primary gingivostomatitis needing treatment, severe or frequent recurrences or immunocompromise. Steroid creams should not be applied to the lesion. The safety issues are eczema herpeticum (a dermatological emergency — rapidly spreading, painful punched-out erosions in eczematous skin, often with fever) and herpes in a newborn, which can be disseminated or affect the brain; the infant may look only mildly unwell at first, so any vesicles, fever, poor feeding or lethargy in a baby under 3 months needs emergency assessment. Children with cold sores do not need to be kept off school. Language matters: explaining that HSV-1 is usually acquired in childhood by non-sexual contact removes stigma and makes the infection-control advice more likely to be followed.