“I’ve got a spreading circular rash on my leg after a walking holiday — is it ringworm?”

A slowly EXPANDING, circular/annular red rash, often with central clearing ("bull’s-eye/target"), appearing days to weeks after exposure in a TICK habitat (woodland, long grass, moorland, deer areas) and typically not very itchy or painful, is ERYTHEMA MIGRANS (EM) — the diagnostic early sign of LYME DISEASE — and many patients do NOT recall a tick bite, so its absence does not exclude it. EM is a CLINICAL diagnosis: when EM is present, TREAT for Lyme with antibiotics (NICE NG95: DOXYCYCLINE 100 mg twice a day for 21 days first-line in adults; amoxicillin for 21 days or azithromycin where doxycycline is contraindicated, e.g. pregnancy/young children) WITHOUT waiting for serology, which is often falsely negative in early disease and not required when EM is present (serology is reserved for when there is no EM but symptoms suggest Lyme). Distinguish EM from tinea/ringworm (scaly itchy advancing edge), cellulitis (hot, tender, acute, unwell), tick-bite hypersensitivity (small, early, non-expanding) and insect-bite reactions, using EM’s slow expansion, large size, target morphology and exposure history. Give practical TICK removal (fine-tipped tweezers/tool, grasp close to the skin, steady pull, do not squeeze/burn) and PREVENTION advice (cover skin, repellent, post-activity body checks). Safety-net the later/disseminated features needing prompt review — NEUROBORRELIOSIS (facial/cranial nerve palsy, radiculopathy, meningitis), Lyme CARDITIS (heart block) and Lyme ARTHRITIS — while reassuring that early treated EM has an excellent prognosis (post-treatment fatigue/aches usually settle). Communicate clearly why this is Lyme rather than ringworm, treat promptly, and address any media-driven anxiety proportionately.