Insect Bite Reactions - Symptoms, Causes & Treatment
Medically reviewed by Dr. Anand S. Urhekar, MD, MD Pathology, Clinical Advisor · Last updated July 2026
Local immune reactions to the saliva of biting insects such as mosquitoes, midges, fleas and bedbugs. They typically appear as itchy red bumps, sometimes with a central punctum or blister, and can produce large local swellings, delayed papular urticaria in sensitised people, or secondary bacterial infection from scratching.
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Quick Answer
Insect bite reactions are itchy red bumps caused by an immune response to insect saliva. Most settle in days with cold compresses, antihistamines and a topical steroid. Warning signs are spreading warm redness with fever (infection), a bullseye rash (Lyme disease), or swelling of the lips, tongue or throat with breathing difficulty (anaphylaxis, a 999 emergency).
Symptoms
- Itchy red bumps, sometimes with a central puncture point
- Blistering in stronger reactions
- Large local swelling around the bite
- Bites in clusters or lines (bedbugs, fleas)
- Recurrent crops of itchy papules in papular urticaria
Causes & Risk Factors
- Mosquitoes, midges and horseflies
- Fleas, bedbugs and mites
- Ticks — with additional risk of Lyme disease
- Individual sensitisation to insect saliva proteins
Treatment & Management
- Cold compresses and elevation for swelling
- Oral antihistamines for itch
- Topical corticosteroid for inflamed bites
- Antibiotics if secondary bacterial infection develops
- Insect repellent, covering skin and treating the source (pets, bedding)
When to See a Doctor
Call emergency services for lip, tongue or throat swelling, wheeze or faintness. See a doctor for spreading warm redness with fever, a bullseye rash after a tick bite, or bites that are not settling after a week.
Frequently Asked Questions
Why do bites affect me more than other people?
Reaction size depends on your individual sensitisation to that insect's saliva proteins. Children and newly exposed adults often react more strongly, and sensitivity typically decreases with repeated exposure over years.
How can I tell a bite from a bacterial infection?
A simple bite is itchy with swelling that peaks within a day or two. Infection is painful rather than itchy, warm, expands after 48 hours and may come with fever — that needs medical review.
Medical References
Information on this page is sourced from and verified against reputable medical resources:
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Medical Disclaimer: This information is for educational purposes only and is not intended as medical advice. The content on this page should not be used to diagnose or treat any health problem. Always consult with a qualified healthcare professional for proper medical evaluation, diagnosis, and treatment of your condition.