GPAtlas🧭 When to suspect
Insect bites and stings are extremely common and almost always cause a self-limiting local reaction. The clinical task in primary care is to separate a benign local reaction from the minority needing action: a large local reaction, a systemic allergic reaction (anaphylaxis), a secondary bacterial infection (usually introduced by scratching), or a vector-borne disease – Lyme disease in the UK, or malaria and arboviral infection after travel.
The single most useful rule is one of timing: a rapid-onset reaction within the first hours of a bite is almost always inflammatory or allergic, not infective, and most bites and stings never need an antibiotic. Infection takes time to develop, typically becoming apparent after 48 hours. Raise suspicion of significant disease in those with previous systemic reactions (the strongest predictor of future anaphylaxis), atopy, high outdoor exposure, recent foreign travel, or tick exposure in woodland, long grass or moorland.
| Reaction | Typical features | Action |
|---|---|---|
| Simple local reaction | Immediate redness, itch and mild swelling at the site; itch and redness may persist up to 10 days | Self-care and reassurance |
| Large local reaction | Swelling >10 cm or crossing a joint; itchy, peaks at 24–48 h; not systemically unwell | Self-care ± short oral steroid; not antibiotics |
| Secondary infection | Increasing pain, spreading erythema, warmth, pus or fever developing after 48 h | Treat as cellulitis |
| Anaphylaxis | Urticaria/angioedema with wheeze, stridor, hoarse voice or hypotension, within minutes | IM adrenaline + 999 |
| Vector-borne disease | Erythema migrans after a UK tick bite; fever/illness after travel | Treat Lyme; urgent assessment if travel-related |
Source: NICE NG182 · NICE NG95
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