Exercise-induced anaphylaxis: triggers, symptoms and what to do

Anaphylaxis is a severe allergic reaction. The NHS says it happens very quickly, usually within minutes of coming into contact with something you are allergic to, and can be caused by food, medicine or insect stings. In exercise-induced anaphylaxis, physical activity is part of what brings the reaction on.

The British Society for Allergy and Clinical Immunology (BSACI) describes the most common pattern as food-dependent, exercise-induced anaphylaxis (FDEIA). Those affected have no symptoms with the trigger food at rest. They react only when it is eaten close in time to exercise. BSACI says the prevalence is unknown, although studies suggest more than 80 per cent of anaphylaxis cases involving exercise could be food related.

This makes the condition confusing for patients and families. The same meal can be eaten safely on a rest day, and a reaction can follow when the same food is eaten before a run or a gym session. For that reason it needs expert assessment rather than self-diagnosis.

The symptoms are those of anaphylaxis. The NHS lists swelling of the throat and tongue, difficulty breathing or breathing very fast, difficulty swallowing, tightness in the throat or a hoarse voice, wheezing, coughing or noisy breathing, feeling tired or confused, feeling faint, dizzy or fainting, skin that feels cold to the touch, and blue, grey or pale skin, lips or tongue. There may also be a rash that is swollen, raised or itchy.

The NHS advises calling 999 if your lips, mouth, throat or tongue suddenly become swollen, you are breathing very fast or struggling to breathe, your throat feels tight or you are struggling to swallow, your skin, tongue or lips turn blue, grey or pale, you suddenly become very confused, drowsy or dizzy, someone faints and cannot be woken, or a child is limp, floppy or not responding as normal.

• Swelling of the lips, mouth, throat or tongue.

• Wheezing, noisy breathing or struggling to breathe.

• Feeling faint, dizzy or confused.

• Pale, blue or grey skin; cold skin.

• A raised, itchy rash.

The NHS lists the steps. Use an adrenaline auto-injector if you have one, following the instructions on the side. Call 999 for an ambulance and say you think you are having an anaphylactic reaction. Lie down, and raise your legs; if you are struggling to breathe, raise your shoulders or sit up slowly, and if pregnant, lie on your left side. If your symptoms have not improved after 5 minutes, use a second adrenaline auto-injector. Do not stand or walk at any time, even if you feel better.

With exercise-induced anaphylaxis, the practical point is to stop exercising at the first sign of symptoms and not to try to push through. The NHS says that anaphylaxis needs to be treated in hospital immediately, with treatments that can include adrenaline by injection or drip, oxygen and fluids by drip, and that you will usually stay in hospital for around 2 to 12 hours, sometimes longer.

BSACI says wheat allergy commonly occurs in infancy and resolves in childhood, but wheat can cause IgE-mediated food allergy in adults, most notably as a common trigger of FDEIA. Although wheat is a common trigger, shellfish, tomatoes, celery, peanuts, maize, soy, strawberries and cheese have all been reported to provoke it.

Co-factors may explain why in some cases food leads to anaphylaxis while in others it causes a milder reaction or none. With co-factors, reactions become more severe or the dose needed to trigger them is lower. BSACI names exercise, NSAIDs (non-steroidal anti-inflammatory painkillers) and alcohol as the most frequently described co-factors, although the underlying mechanisms are poorly understood. In some cases co-factors may be suspected but not identified, and more than one may be involved.

The NHS says that after anaphylaxis you may be referred to an allergy specialist for tests and advice, and that before leaving hospital you should be given 2 adrenaline auto-injectors, or a prescription for them, and shown how to use them. Diagnosing the exercise-related pattern is a matter for an allergy clinic, which takes a careful history of what was eaten, what exercise was done and any medicines or alcohol taken beforehand.

Because the trigger may be a food that is tolerated at other times, people are often asked to keep a diary of meals, activity and symptoms to bring to the clinic.

The NHS advises avoiding what you are allergic to, carrying 2 adrenaline auto-injectors at all times, checking expiry dates regularly, practising with a trainer injector, teaching friends, family, colleagues or carers when and how to use it, and wearing medical alert jewellery. It also says not to leave auto-injectors anywhere too hot or cold, such as the fridge or outside in the sun.

For exercise-related reactions, specialists commonly give individual advice about the timing of meals before exercise, avoiding identified trigger foods, and avoiding NSAIDs or alcohol around exercise; the details depend on your own pattern and should come from your allergy team. Exercising with other people who know about your condition and what to do is a sensible precaution.

On the NHS, a GP can refer you to an allergy service after an episode of anaphylaxis, and emergency treatment is free at the point of use. Adrenaline auto-injectors are prescribed on the NHS.

Private allergy clinics offer assessment and tests, sometimes with shorter waits, and some people use them for a second opinion. The key point is that the diagnosis is made by someone experienced in exercise-related allergy, whichever setting you choose.