Popular Science reports that exercise-induced anaphylaxis, which is thought to affect 50 in every 100,000 people, can cause hives, swelling and nausea in response to exercise. While the specific cause is not yet known, food can be a trigger (usually when wheat or shellfish is consumed the same day as exercise) as can taking aspirin.
The only workout that no-one seems to be allergic to? Swimming. A study published in Current Allergy and Asthma, reports Business Insider, found that people diagnosed with exercise-induced anaphylaxis didn’t present any symptoms after doing laps.