Sometimes when I exercise, I get hives on my arms or the back of my legs. It's a bit like when I go near a horse and get an allergic reaction, but without the itchiness and inability to breathe.

This puts me on the lower end of the spectrum of having "exercise-induced anaphylaxis," or EIA. It's basically an allergy to exercise, and it affects about 2 percent of the population.

It most often happens after vigorous physical activity like jogging, tennis, dancing, and bicycling. But lower levels of exercise such as walking can also cause a reaction.

My EIA isn't severe enough to make me stop running, but for other people it can be. In some rare cases, it can even be deadly.

It's quite similar to other allergies, which differ in severity from person to person. During an allergic reaction, your immune system makes antibodies - proteins in the blood that fight bacteria and foreign bodies.

When someone with EIA exercises, antibodies are produced to fight against something, even though they aren't needed.

Antibodies release several different immune system chemicals, such as histamine, which cause allergy symptoms like a runny nose and inflamed skin.

EIA symptoms include hives, flushing, wheezing, and sometimes digestion problems. If you keep exercising when it occurs, your reaction could get more severe, such as throat closing, or low blood pressure, which can lead to circulatory failure.

That all sounds pretty scary. And it's the main reason I still take my inhaler to the gym, even though I haven't really needed it for several years.

It might be caused by your diet

Doctors don't always know what causes it. In many cases, people experience a subset of EIA called food-dependent exercise-induced anaphylaxis (FDEIA). This is when you exercise soon after eating a specific food, and it causes a reaction.

You might not usually have any allergic symptoms when you eat the food normally, but something about the combination of physical exertion and the food sets off your immune system.

According to Medscape, the most common foods linked to FDEIA are wheat, shellfish, tomatoes, peanuts, and corn. But other foods have been reported to have an impact too, like meat, fruit, seeds, milk, soy, lettuce, peas, beans, and rice.

It might not be as simple as avoiding these foods, though, as there is also a nonspecific form of FDEIA, where eating any food before exercise can kick off a reaction.

There's also a chance it is something you're breathing in, such as dust mite debris, or mould spores.

It probably won't go away

Unfortunately, the only way to prevent EIA is by exercising at a lower intensity. Or, you can change the type of exercise you do, as swimming hasn't been associated with EIA.

If you suspect food is inducing the reaction, the medical recommendation is to stop eating six to eight hours before exercising. Very hot or cold weather can also worsen the reaction, so avoid working out during those times.

Depending on the severity of your reaction, it might also be a good idea to see a doctor and get an Epipen, which is filled with emergency injectable adrenaline (epinephrine) that stops the reaction.

This article was originally published by Business Insider.

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