It's not always an excuse to avoid a workout.

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It's hard to argue that exercise is bad for your health in the face of an enormous body of evidence that tells us otherwise. But for some people, such as TikTok user Kira (@snflwrxtrnsl), exercise actually is harmful—because her doctors believe it caused her to have a serious allergic reaction.

In a recent video posted to TikTok, Kira mouths the lyrics to Lady Gaga's "Bad Romance" against a backdrop montage of images. The first, showing her outdoors in running gear, is captioned, "me going on a normal run for gym class." The next says, "me getting really tired way too fast but thinking nothing of it."

Then it gets more serious. "My whole body starting to itch like crazy and my face blowing up," she wrote. She goes on to reveal that she had to call her mom to pick her up because she was feeling faint and had trouble breathing. But her ordeal wasn't over. Back home, she and her mom had to call 911 because she was "becoming blind." The next image was of Kira in the back of an ambulance, with the caption, "me rushed to the hospital given 3 epipens on the way." She finished the clip by revealing that her doctor told her she was "probably allergic to exercise."

In the comments, Kira revealed that she "literally got a doctors note so I can't do gym class anymore."

How can someone be allergic to exercise?

While we don't know for sure if Kira was indeed allergic to exercise, it's possible...kind of. A rare condition called exercise-induced anaphylaxis (EIA) occurs when someone reacts to an allergen in conjunction with exercise. It was first described in 1979 in a case report published in the Journal of Allergy and Clinical Immunology, and is thought to affect around 50 in every 100,000 people.

"Exercise-induced anaphylaxis is a rare entity that occurs when people go into a life-threatening severe allergic reaction that can include wheezing, rash, breathing issues, and shock," Purvi Parikh, MD, an allergist and immunologist at NYU Langone Health, tells Health.

There's also a subtype of EIA known as food-dependent exercise-induced anaphylaxis (FDEIA), where both trigger foods and physical activity are required to induce anaphylaxis. "Prevalence of FDEIA is not well known, but it has been reported to be about a third or half of all EIA cases. Symptoms and presentations are similar to those of EIA, and people with this syndrome don't react to the food or the exercise alone," Brian Jin Choi, DO, a sports medicine physician with Hoag Orthopedic Institute in Orange County, California, tells Health.

What are the symptoms?

Common symptoms include the typical symptoms of an allergic reaction, including but not limited to itchy skin, hives, angioedema (swelling underneath the skin), flushing, shortness of breath, gastrointestinal symptoms (e.g. nausea and diarrhea), headache, and loss of consciousness, Dr. Jin Choi says. He adds that death from this condition is very rare, but it should still be considered as potentially life-threatening.

What causes EIA/FDEIA?

It's not clear. "The exact mechanism between exercise and anaphylaxis is poorly understood, but there is a link between foods that are eaten within three hours of heavy exercise that trigger this reaction," Dr. Parikh says. Any food can be a trigger, but common culprits are shellfish, wheat, seafood, nuts, cereal, dairy, and celery. It may also be exacerbated by alcohol intake, or ingestion of aspirin or non-steroidal anti-inflammatory drugs (NSAIDs).

EIA/FDEIA is usually triggered by moderate-intensity exercises, most commonly jogging, but can occur with any intensity level of exercise. "Episodes are not fully predictable, in other words the same intensity and type of exercise may or may not induce the symptoms every time," Dr. Jin Choi says. "Some external factors may play a role as well, such as humidity and warm or cold weather."

There are various theories about what's going on, such as increased blood flow in the body during exercise, which might displace sensitive immune cells. Another is that some proteins in the gut behave in a certain way during physical activity and interact with food or medication in a way that causes an allergic reaction.

Are there any risk factors?

EIA/FDEIA can occur in any age group, but it appears to be most common in the teens and 20s, Dr. Jin Choi says. "There is no known racial predilection and no clear gender predilection, although two large studies have reported that females are twice as likely to experience it than males."

Does fitness level have anything to do with it?

It's unlikely. "There appears to be no relationship between fitness level and the predilection to EIA or FDEIA," says Dr. Jin Choi. "It is usually sporadic, but some cases are reported to be hereditary."

How is it treated, and is there a cure?

After an EIA/FDEIA reaction, the management methods are similar to those used to treat regular anaphylaxis, Dr. Jin Choi says. These include intramuscular epinephrine, antihistamine, systemic steroid, fluid resuscitation, and supportive care.

No, but there are various preventive steps you can take. The most important step is to avoid foods or medication that can trigger symptoms close to the time of exercising. Dr. Jin Choi also recommends avoiding exercise in hot, cold, or humid weather. Dr. Parikh suggests taking an antihistamine (like Zyrtec) 30 minutes before exercising. "I prescribe all my patients with exercise-induced anaphylaxis an EpiPen to keep close by," she adds.

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