Severe Mosquito Bite Reaction: What to Know

Mosquito saliva can trigger a strong local immune response. The area may become red, hot, swollen and very itchy, sometimes with a blister or a broad patch extending beyond the bite. Several bites can make the reaction look dramatic. Scratching can break the skin and allow bacteria to enter; increasing pain, pus or spreading redness points more toward infection than simple bite irritation.

A bite reaction is different from anaphylaxis. Breathing difficulty, throat tightness, faintness, or swelling of the lips and tongue are emergency symptoms, regardless of how the skin looks.

Wash the skin gently, then use a cool compress for short intervals to reduce heat and swelling. Keep fingernails short and avoid scratching or squeezing a blister. A pharmacist or clinician can advise whether an oral antihistamine or a short course of a topical corticosteroid is suitable; these options are explained in Antihistamine Treatment and Topical Corticosteroids.

Cover an open area with a clean dressing and check it regularly. Photographing the edge of redness can help you notice whether it is spreading. Repellent, long clothing and screens can reduce further bites.

Get emergency help for trouble breathing, wheezing, dizziness, collapse, or swelling of the mouth or throat. Arrange prompt medical review if swelling is rapidly expanding, pain is worsening, the skin is increasingly hot, pus develops, fever appears, or the reaction affects an eye. A clinician should assess a large or persistent reaction, especially in a child or someone with a history of serious allergy.

Ask whether the appearance fits a large local bite reaction, infection, or another rash; which medicine and duration are appropriate; and how to recognise an allergy emergency in the future.