“Want to go running?”

“Sorry, I’m allergic.”

It may sound like the perfect excuse, but can skipping the dreaded Phys Ed Mile or steering clear of running clubs actually be justified? Here’s some good (or bad) news — depending on that level of running love. People can in fact experience an allergic reaction to aerobic exercise, although it’s generally pretty rare^[1].

No Runny Business — Why It Matters

Photo by Jordan Shakeshaft

People usually associate working out with an increased heart rate and a nice rush of endorphins — not hives, fainting, or an itchy rash^[2]. But it could happen: Cholinergic urticaria, a common type of heat rash, can make an irritating appearance when there’s an increase in body temperature or when mast cells in the skin break down right before releasing sweat (read: working out). Studies suggest up to 11 percent of young adults experience this post-exercise hive attack, which is slightly more common in men. 

Even worse: There’s a running allergy that can be fatal. Exercise-induced anaphylaxis is a (very) rare allergy that occurs after eating certain foods like wheat, shellfish, and peanuts — and, like the name suggests, it’s triggered by exercise (especially running)^[3]. Waiting at the finish line for sufferers: vomiting, difficulty breathing, and hives — notthe normal post-run experience. But before hanging up the sneakers and camping out on the couch, the chances of encountering this allergy are extremely low. Researchers estimate it only affects less than half a percent of the Western population (though methods of measuring prevalence haven’t been entirely pinned down yet)^[4].

Sneeze Louise — The Answer/Debate

Running may not be everyone’s favorite fitness activity, but the “I’m allergic” excuse is reserved for those (un)lucky few. Besides the low risk of allergy, only one death from exercise-induced anaphylaxis has been recorded in the past 40 years. And there’s an easy way to prevent an outbreak from this food and exercise allergy: Work out before breakfast, since the reaction occurs only when exercise follows the food.

As for the itchy cholinergic urticaria, its cause is a sudden spike in body temperature, so a slow warm-up may help those temps rise slowly to avoid a sudden breakout^[5]. Best to skip the Bikram Yoga, though. Or, mix things up and hit the pool to keep the body temperature cool^[6].

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