Horsefly bite allergy
Painful reactions to horsefly bites.
About horsefly bite allergy
Horseflies are large biting flies whose females cut the skin with scissor-like mouthparts to feed on blood, which is why their bites are notably painful rather than a simple prick. The reaction that follows is partly to substances in the fly's saliva, and sensitivity varies between people. Bites are more common in warm weather and near water, woodland and livestock, and outdoor workers, walkers and riders are more likely to be bitten on exposed skin.
Reactions usually appear within minutes and can include a painful, red, raised and itchy weal, often larger and slower to settle than many other insect bites. Because the bite breaks the skin, there is a greater chance of secondary bacterial infection, which may show as increasing pain, spreading redness, warmth or pus over the following days. Most people have a local reaction that settles over a few days to a week or so, though some develop larger swellings, and more marked allergic reactions are uncommon.
Management centres on cleaning the bite, relieving the itch and watching for infection. Keeping the area clean, avoiding scratching and using measures suggested by a pharmacist can help, and a GP should be consulted if the bite becomes infected, blisters, or the reaction is severe or spreading. Covering exposed skin and using insect repellent can reduce bites outdoors. As with any insect bite, a rare severe whole-body reaction with breathing difficulty, widespread swelling or collapse is a medical emergency requiring 999.
Common triggers
- Horsefly bite and products containing it
Symptoms
- Pain, redness and swelling at the sting or bite
- Widespread hives or itching
- Swelling of the face, lips or throat
- Wheezing or difficulty breathing
- Anaphylaxis in severe cases
Avoidance & management
- Avoid nests, hives and known habitats
- Wear covering clothing and avoid strong scents outdoors
- Use insect repellent and screens
- Carry an adrenaline auto-injector if prescribed
- Seek urgent help for a severe reaction
Sources & references
Allergy safety: what everyone should know
Mild-to-moderate reaction signs
- Itching, hives or a raised rash
- Swelling of lips, face or eyes
- Tingling mouth, sneezing, runny nose
- Stomach pain, nausea or vomiting
Anaphylaxis — call 999 (UK) or 112 (EU) immediately
- Difficult or noisy breathing, wheeze, persistent cough
- Swelling of the tongue or tightness in the throat
- Dizziness, collapse, pale and floppy (young children)
- Use an adrenaline auto-injector (e.g. EpiPen) at once if prescribed, then call an ambulance even if symptoms improve
Allergy or intolerance? A true allergy involves the immune system and can escalate quickly; an intolerance (e.g. lactose intolerance) is unpleasant but not life-threatening. The symptoms overlap, so self-diagnosis is unreliable.
Getting tested: home-testing kits based on IgG are not diagnostically valid. If you suspect an allergy, ask a GP for referral to an allergy clinic for skin-prick or specific-IgE testing and a supervised food challenge where appropriate.