Description
Horse flies (Tabanus spp.) are not typical biters. Unlike mosquitoes, which pierce the skin cleanly, female horse flies use scissor-like mandibles to slash the skin open and lap up the resulting pool of blood. In doing so, they inject saliva loaded with anticoagulants and allergenic proteins directly into the wound. For people whose immune systems have become sensitised to these proteins — allergen code i204 — even a single bite can trigger a significant allergic reaction.
Our horse fly venom allergy test detects specific IgE antibodies to i204 in your blood, giving you the clinical evidence you need to understand what’s happening in your body and take action.
Symptoms of a horse fly allergy
A typical horse fly bite causes localised pain, redness, and minor swelling — a normal response to the wound. If you notice any of the following beyond the immediate bite area, or if your reaction seems disproportionately severe, this may point to an IgE-mediated allergic reaction to the fly’s salivary proteins.
Large, spreading welts — redness and raised skin extending well beyond the original bite site
Significant swelling — oedema affecting a wide area around the bite, sometimes an entire limb
Hives (urticaria) — itchy, raised welts appearing on parts of the body away from the bite
Wheezing or breathlessness — difficulty breathing or a tight sensation in the chest
Dizziness or feeling faint — light-headedness, weakness, or a sudden drop in blood pressure
Nausea or vomiting — stomach discomfort as part of a systemic immune response
Facial swelling — puffiness around the eyes, lips, or tongue (angioedema)
Rapid heart rate — a racing pulse or palpitations following the bite
⚠️ When to call 999 immediately
Swelling of the lips, tongue, or throat, difficulty breathing or swallowing, loss of consciousness, or rapidly worsening symptoms are signs of anaphylaxis — a life-threatening emergency. Call 999 without delay. If you carry an adrenaline auto-injector (EpiPen), use it immediately and still call for an ambulance.
What is a horse fly allergy?
Horse fly allergy is an immune-mediated hypersensitivity to proteins found in the saliva of Tabanus spp. — collectively referred to as allergen i204 in standardised IgE testing. When a sensitised person is bitten, their immune system recognises these salivary proteins as threats and mounts a rapid IgE-mediated (Type I hypersensitivity) response, releasing histamine and other inflammatory mediators that cause the symptoms above.
Horse flies belong to the family Tabanidae — one of the most widespread families of blood-feeding insects, with over 4,500 species globally. They are most abundant in rural and wetland areas and are particularly active during warm months in the UK from late spring through early autumn.
-
◆
Three major allergens have been characterised in Tabanus saliva: Tab y 1, Tab y 2, and Tab y 5 -
◆
Tab y 2 and Tab y 5 show cross-reactivity with homologous wasp venom proteins (Ves v 2 and Ves v 5) — a phenomenon known as “wasp-horsefly syndrome” -
◆
Reliable identification of the biting insect is rarely possible in clinical practice, meaning horse fly allergy is often under-diagnosed -
◆
Systemic reactions range from generalised urticaria to anaphylaxis — cases of Tabanus-induced anaphylaxis requiring emergency epinephrine have been documented in medical literature since the 1990s -
◆
Horse fly saliva contains pharmacologically active compounds that suppress the body’s innate immune system, making bites particularly slow to heal
Wasp allergy and horse fly allergy may go hand in hand. If you have a known wasp venom allergy, research suggests you may be at higher risk of systemic reactions to horse fly bites — and vice versa. Testing for i204 alongside wasp venom allergens gives a fuller picture of your insect hypersensitivity profile.
Why can a horse fly allergy be a serious problem?
For most people a horse fly bite is an unpleasant but short-lived experience. For those with i204 sensitisation, however, the picture is very different. Horse flies are common throughout rural Britain — near rivers, ponds, farmland, and woodland — during the very months when people are most likely to be outdoors.
Countryside walks, horse riding, wild swimming, gardening, camping, and outdoor sports all carry a risk of exposure. For someone with an undiagnosed horse fly allergy, each of these activities carries the hidden risk of a serious or even life-threatening reaction.
Knowing you have a horse fly allergy allows you to take practical steps: carry an antihistamine, discuss an adrenaline auto-injector with your GP, wear appropriate clothing outdoors, and seek specialist allergy advice. Without a diagnosis, the risk remains invisible.
How the test works
No clinic visit needed. The entire process is completed from home.
Order & receive
Your kit arrives by post — lancets, sample cards, instructions, and a pre-paid return envelope.
Collect your sample
Two simple finger-prick blood drops at home, with clear step-by-step guidance.
Post it back
Use the pre-paid return envelope — no extra cost or arrangements needed.
Receive results
Your i204 IgE results appear in your secure portal within 1 week of sample receipt.
Why choose our horse fly allergy test?
Clinically validated accuracy
Specific IgE testing measuring antibodies to i204 (Tabanus spp.) with precision and reliability.
True home collection
Two finger-prick samples at your convenience — no waiting rooms, no phlebotomist appointment.
Standardised allergen code
We test for allergen i204 — the internationally standardised code used in clinical and research settings worldwide.
Expert follow-up
Our allergy specialists provide tailored guidance once your results are ready.
Secure results portal
Results delivered privately to your personal portal — accessible any time, ready to share with your GP or allergist.
Test multiple allergens at once
Remote collection supports up to 3 allergens from the same sample. Laboratory collection has no limit.
Test details at a glance
- ✓Allergen: Horse fly (Tabanus spp.) — allergen code i204
- ✓Test type: Specific IgE blood test
- ✓Sample: Finger-prick (two samples included in the kit)
- ✓Collection: Remote (home) or laboratory
- ✓Remote: up to 3 allergens from a single sample per checkout
- ✓Laboratory: unlimited allergens simultaneously
- ✓Turnaround: results within 1 week of sample receipt
- ✓Results delivered to your secure patient portal
Frequently asked questions
Can you genuinely be allergic to horse flies?
Yes. When a female horse fly bites, she injects saliva containing anticoagulants and allergenic proteins (i204). In sensitised individuals, the immune system raises IgE antibodies against these proteins, and subsequent bites trigger reactions ranging from large local swelling to systemic urticaria and, in rare cases, anaphylaxis.
How is a horse fly allergy different from a normal bite reaction?
Almost everyone bitten by a horse fly will experience pain, localised redness, and minor swelling — that’s a normal wound response. An allergic reaction involves the immune system and typically causes disproportionately large swelling, hives away from the bite site, dizziness, breathing difficulties, or systemic symptoms within minutes to an hour of the bite.
What does the test actually measure?
The test measures the level of specific IgE antibodies in your blood directed at i204 — the standardised allergen code for Tabanus spp. (horse fly) salivary proteins. Elevated specific IgE to i204 indicates sensitisation to horse fly venom/saliva.
I have a wasp venom allergy — should I also test for i204?
Possibly, yes. Medical literature describes a “wasp-horsefly syndrome” in which patients allergic to wasp venom proteins (Ves v 2 and Ves v 5) also experience systemic reactions to horse fly bites, due to cross-reactivity with Tab y 2 and Tab y 5 in horse fly saliva. If you have a known Hymenoptera venom allergy, discussing i204 testing with your allergist is worthwhile.
What should I do after receiving a positive result?
Share your results with your GP or an NHS allergist. They may refer you for further evaluation, advice on carrying an adrenaline auto-injector (EpiPen), and guidance on managing future bites. Our team is also available to provide initial guidance following your results.
Can I test for horse fly allergy alongside other insect bite allergens?
Yes. With remote (home) collection, up to 3 allergens can be tested from a single sample in one checkout. For laboratory collection there is no limit — making it easy to test for wasp, bee, mosquito, and other insect allergens at the same time.
How do I access my results?
Results are delivered to your secure patient portal within 1 week of sample receipt. Register before sending your sample at ukallergy.carebit.co/patients/accounts/sign-up.
This allergy test is suitable for self-collection (remote) or laboratory sample collection. Remote collection supports up to 3 allergens per sample per checkout; laboratory collection has no limit. Results are delivered to your secure patient portal within 1 week of sample receipt. This test is for informational purposes only and does not constitute medical advice. If you suspect anaphylaxis, call 999 immediately.
