Yes, you can be allergic to exercise — and the symptoms can be dangerous

People who don’t like to workout will sometimes joke that they’re “allergic” to exercise. But what many don’t realise is that an allergy to exercise is a real thing – and it can be dangerous if not caught in time.

Exercise-induced anaphylaxis (EIA) is a rarely heard of severe allergic reaction to moderate exercise. It can cause intense itching all over the body, followed rapidly by an inability to breathe. It’s estimated that between 2.3% to 5% of all cases of anaphylaxis globally are triggered by exercise.

EIA was first identified in the 1970s by doctors in Colorado after a 30-year-old long-distance runner was hospitalised multiple times, a few days apart, while he was out on a run.

Further testing revealed that his blood contained all the tell-tale signatures of anaphylaxis (an allergic reaction). Intrigued, they investigated further and quickly discovered that the runner only developed allergic symptoms when he exercised after eating seafood. When he didn’t eat seafood before exercise, he had no symptoms.

It’s now well established that not all cases of EIA are triggered by food allergens. This sub-type is known specifically as food dependent EIA. It’s commonly triggered by foods such a shellfish, nuts, eggs, milk and wheat.

But EIA symptoms can also arise when exercise follows exposure to a range of other factors, including certain medications, infections, hormonal changes, alcohol consumption or even environmental triggers such as pollen. In some cases, exercise alone triggers a reaction.

Symptoms of EIA are similar to those seen with other allergic reactions. An itchy rash, swelling of the lips, tingling mouth and even vomiting after exercise have all been reported. In severe cases, it can also result in problems with breathing and circulation.

Exercise-induced anaphylaxis appears to most commonly be triggered by aerobic exercise – such as jogging, football, dancing and even gardening. EIA can occur equally across all ages and sexes but tends to be first diagnosed in young adulthood.

One study which followed patients diagnosed with EIA over a period of ten years found that most patients’ symptoms reduced or stabilised over time. However, this could be due to participants taking precautions to reduce triggers – such as not performing vigorous exercise.

Exercise allergy

Despite years of research, the exact cause of exercise-induced anaphylaxis remains unclear.

Initially, scientists and doctors suggested it was just a food allergy. But studies since have demonstrated otherwise.

The closest we have come to understanding the cause of EIA comes from recent oral immunotherapy trials, where people allergic to foods such as peanuts or wheat were given small doses of the food daily to train their immune system to tolerate the food. It was found that this immune training could be undone if the same, low-dose of food was eaten followed by exercise – resulting in an allergic reaction. In fact, scientists calculated that eating roughly half as much food could still trigger an allergic reaction when followed by exercise.

Researchers have also reported cases of people with no known allergies developing repeated anaphylaxis following moderate to vigorous aerobic exercise.

This raises the possibility that an unknown or hidden allergen is involved, or that exercise itself can act as the trigger. Interestingly, when looking at the participants in the oral immunotherapy study, moderate to vigorous exercise didn’t always trigger anaphylaxis – even when they ate the food that normally triggered an allergic reaction before exercising.

This shows us that it can be difficult to predict when EIA will hit. It also suggests that additional, currently unidentified factors may also play a role in provoking symptoms.

However, most scientists currently believe that a type of immune cell, called a mast cell, plays a central role in exercise-induced anaphylaxis.

Mast cells release chemicals into the bloodstream, including histamine. Under normal circumstances, histamine helps control blood flow, mucus production and opening of the airways to protect us from infection or injury. But in allergic reactions, histamine is responsible for inducing common symptoms such as itching, flushing and a narrowing of the airways.

In cases of EIA, mast cells appear to be activated at the wrong time, causing a sudden surge of histamine that constricts the airways and blood vessels, resulting in anaphylaxis.

The main aim with treating exercise-induced anaphylaxis is to reduce both the severity and the frequency of reactions. This is usually achieved through behavioural changes, such as starting with low-intensity activity and gradually increasing intensity to identify personal limits.

For people with a known allergy, experts recommend avoiding exercise for at least four hours after exposure to the trigger.

Carrying an adrenaline auto-injector, such as an EpiPen, at all times is essential if you’ve been diagnosed with EIA. Exercising with a partner who can recognise symptoms and intervene if needed is also strongly advised.

Crucially, exercise should be stopped immediately at the first sign of symptoms. In those with milder reactions, antihistamines may also be prescribed to help manage symptoms.

The good news is that most people diagnosed with EIA manage to live relatively normal, active lives through a combination of awareness, behavioural adjustments and medication. But it’s important to stay prepared if this has ever happened to you, so that a healthy habit doesn’t turn into a medical emergency.