Peter Forshaw was running up the pitch during a 'lads v dads' football match when he suddenly felt an itchy sensation across his arms – and seconds later found himself struggling to breathe.

'I was running around when I started getting itchy on my chest and arms, which I'd never had before,' says the married father-of-one. 'Then my throat started itching, then swelling.'

Soon Peter, then aged 43, was on his knees gasping for air. Worried players ran over thinking it was a heart attack and one of them called 999 and paramedics rapidly arrived who rushed him to hospital.

But curiously tests rapidly ruled out a heart attack. 'It was then the doctor saw my hives and ran some basic allergy pinprick tests,' says Peter.

'But they came back as negative too,' he says.

Peter was discharged without knowing what had caused the frightening episode.

Later his wife reminded him that they had eaten breaded scampi earlier that day and they thought it might have been food poisoning.

It would be more than ten years before Peter would find out the true cause – and even then only after he had another, potentially life-threatening episode.

Peter, 68, a retired lorry mechanic from south-east London, has a form of exercise-induced allergy, known as exercise induced anaphylaxis, meaning that any exertion that raises his heart rate above resting can provoke a serious reaction.

Peter, 68, a retired lorry mechanic from southeast London, has a form of exercise-induced allergy, known as exercise induced anaphylaxis

It means that even a brisk walk could potentially be life-threatening for him.

Anaphylaxis is a severe, potentially life-threatening allergic reaction which can be triggered by many things including foods such as nuts, an insect bite – and exercise.

The immune system overreacts and immune cells release a flood of chemicals such as histamine that can affect the entire body, 'widening blood vessels and making them leak,' says Dr Scott Pereira, a consultant immunologist at Medical Express Clinic, a private clinic in London.

The leaked blood and fluid causes flushing, hives and swelling; meanwhile the same chemicals tighten the airways, making it difficult to breathe.

The chemicals also 'irritate the gut, causing pain and nausea; and if enough fluid leaks out of the circulation, blood pressure falls and the person collapses,' says Dr Pereira.

In the case of exercise-induced anaphylaxis the reaction is provoked most often by a food but the immune system doesn't start to overreact until someone exercises, he adds.

Most commonly it is a protein called omega-5 gliadin found in wheat which is the culprit.

'However, shellfish, nuts, celery and tomatoes have also been implicated,' says Dr Pereira.

'Interestingly, many people can eat these foods without any problem when resting and can exercise safely when they haven't eaten them.

'It is the combination of eating the trigger food followed by exercise that causes the reaction.'

So while the immune system has antibodies to the foods in question 'exercise is what pulls the trigger' for the reaction says Dr Pereira.

The reason exercise provokes this reaction is that 'it makes the gut wall temporarily more permeable, so far more of the food protein passes into the bloodstream than usually would,' says Dr Pereira.

'Exercise also redistributes blood flow and raises core body temperature - each of these appears to make the immune cells more unstable and readier to release their contents.'

What's more at rest food 'is absorbed slowly and in small amounts and stays below the threshold that would provoke a reaction.

'During exercise, a large amount enters the bloodstream quickly and reaches the whole body at once, so the response is systemic from the outset rather than confined to the gut or the skin,' he says.

'Add to that the fact that the circulation is already working hard, and you have the conditions for a full anaphylactic reaction rather than a mild one.'

Even a brisk walk could potentially be life-threatening for Peter due to his condition

Peter said he suddenly recalled that in every allergic episode he had been exercising such as playing football, or lifting heavy equipment at work

Typically exercise-induced anaphylaxis begins when someone is a teenager or hits their twenties but can happen at any age. Diagnosis can be complex, says Dr Pereira, 'because exercise is often only one part of the picture.'

'Other factors, including alcohol, anti-inflammatory painkillers such as ibuprofen, infections, high pollen levels and hormonal changes, can lower the threshold at which a reaction occurs.

'Then a combination lines up on one day: the food, the exercise, perhaps a painkiller, a drink the night before, high pollen, feeling run down. Any one of these lowers the threshold. Stack a few together and the person finally crosses it.'

What's more he says the co-factors that lower the threshold tend to accumulate with age, but why this happens is not known.

Exercise-induced anaphylaxis accounts for roughly 5 per cent of all cases of anaphylaxis – but while it is rare, Dr Pereira says it is also probably under-recognised.

After the incident on the football pitch, it wasn't until 12 years later, in 2014, that Peter had another attack. This time it occurred as he changed an axle on a truck – a physically taxing task that made him break into a sweat – after eating a cheese roll and a digestive biscuit

Suddenly he broke out in hives across his chest and neck, and he was quickly gasping for air.

'I fell to the floor, clutching my throat,' he recalls.

'A colleague tried first aid, but I couldn't breathe, I was thrashing around and they called an ambulance.'

He was rushed to hospital and this time diagnosed with atrial fibrillation (AF) – an irregular heart rhythm that starts in the heart's upper chambers and causes fatigue, shortness of breath, palpitations, and dizziness.

He was given a beta blocker, medication to slow his heart rate and referred to a cardiologist.

Worried about the NHS waiting times he decided to use private health insurance, to see one quicker.

Days later a private consultant ran tests on his heart and looking confused told him: 'There is absolutely nothing wrong with your heart.'

'I was confused because the GP and NHS consultant had me convinced I had AF, now this guy was saying my heart was great,' says Peter.

The cardiologist suggested Peter have more extensive allergy testing including skin prick testing as well as blood tests.

The pinprick tests – where tiny amounts of a potential allergen are pricked into the skin found that Peter was allergic to wheat and sulphites (found in wine and other alcohol).

From this doctors concluded that wheat or sulphites had caused the allergy but it was exercise that caused the severe reaction and anaphylaxis.

'I suddenly recalled that in every episode I had been playing football, or lifting heavy equipment at work - basically exercising,' says Peter.

He recalled hurrying for a bus and collapsing on board in 2008, with passengers desperately trying to administer first aid.

'Thankfully someone called an ambulance,' says Peter.

'Other times I'd been doing strenuous things like football or heavy lifting – this was hardly more than a brisk walk.'

Dr Pereira says: 'Exercise-induced anaphylaxis like any form of anaphylaxis, can be fatal if not recognised and treated promptly.

Once diagnosed people will be advised to avoid the triggers that cause the reaction, for example leaving at least four to six hours between eating a trigger food and exercising.

'The relevant food proteins can still be circulating for several hours after a meal, so the four-to-six-hour window is designed to make sure they have cleared before exercise begins,' says Dr Pereira. 'It is a practical safety margin rather than a precise biological cut-off, and for some people the sensible gap is longer. '

'Most people diagnosed with exercise-induced anaphylaxis are also prescribed adrenaline auto-injectors, such as an EpiPen,' says Dr Pereira. These help by expanding the airways and tightening blood vessels.

'They should also receive education about recognising symptoms early, stopping exercise immediately if symptoms develop, and using adrenaline promptly rather than waiting to see if symptoms worsen.'

Peter was given an EpiPen – an adrenaline injector designed for emergency use in people experiencing anaphylaxis and was told to avoid any exercise.

'I thought I had it under control,' he says.

'I avoided wheat, never exercised or exerted myself and thought that was that.'

But he still must be careful.

In spring 2022, Peter was returning home from lunch with his wife and had to run to make the train.

'It was only a 20-minute journey, but I felt unwell so I used my Epi-Pen when I reached my stop. Then I collapsed.'

His wife rang 999 explaining he was in anaphylactic shock.

'My wife was pleading with them to send an ambulance,' he recalls.

Thankfully an off-duty nurse came to help while they waited for an ambulance to arrive and Peter was taken to hospital.

Now Peter has two EpiPens and does gentle exercise but makes sure he doesn't eat any wheat products for about six hours prior or four hours afterwards.

'If we fly on holiday, I have to get there hours early as I cannot walk fast for the gate for the flight. I can't lift luggage, I can't queue, I can't brisk walk in case I've eaten anything in the hours prior. It's affected everything.

'I love the NHS, but they are not equipped for the extensive allergy and anaphylaxis testing I needed to diagnose my condition,' he says.

'Without that, just running for a train could have killed me by now.'