"They have all of the manifestations one would have if you had an acute allergic reaction to peanuts," explained Dr. Thomas Casale, chief of allergy and immunology at Creighton University and executive vice president of the American Academy of Allergy, Asthma & Immunology.
Most often reported with running or jogging, the exercise-allergic person might get hives, swelling, trouble breathing, low blood pressure, itching, nausea, a headache or wheezing.
Because some of the symptoms occur commonly during normal exercise, some people with exercise-induced anaphylaxis might not realize they have the problem.
In addition, for some people, the reaction only comes when exercise is combined with a certain food. Casale noted several early reports of exercise-induced anaphylaxis from people who ate celery before they exercised.
"They could exercise, they were fine. They could eat celery, they were fine. They eat celery, then they exercise -- then they have an anaphylactic reaction," said Casale, who studied the phenomenon in the 1980s.
As is typical with most allergic reactions, the symptoms of exercise-induced anaphylaxis result from chemicals -- including histamines -- that are released by mast cells in the body. But Casale said researchers have yet to figure out why exercise, or the food/exercise combination, triggers the mast cells to act.
Still, doctors say there are ways for the afflicted to exercise and stay safe. You can exercise with a buddy, carrying adrenaline, and in the case of those with food triggers, avoid meals for two to four hours before and after exercise, Casale suggested.
About one in five people will develop hives at some point in their lives, but a much smaller number will get physical urticarias (urticaria is another word for hives) when they contact or experience some very ordinary things.
"If you put an ice cube on somebody that has cold urticaria, they're going to have a big welt right where the ice cube was," said Casale. And it's not just the cold. "It could be heat, could be sunlight. It could be vibration. It could be pressure."
In fact, some cases of heat-induced hives might be confused with exercise-induced anaphylaxis because exercise can raise body temperature.
Casale found the two could be distinguished for diagnosis by either heating the patient using a warming blanket or placing the patient's hand or leg in hot water. Only those with heat urticaria will develop hives.
An even smaller number of people with the condition may be diagnosed with aquagenic urticaria, meaning they are allergic to water.
"I actually saw a patient probably six or seven years ago. We put water on her and, boy, she just broke out in hives where the water hit her," said Casale, although he thought the reaction might have been provoked more so by the temperature of the water than the water itself.
There's no treatment for physical urticaria and "we still don't have a really good clue as to how [the hives] come about," said Casale. "These syndromes aren't extremely common and they're very difficult to study."
The pine processionary caterpillar and its cousin, the oak processionary caterpillar, look harmless enough, but the hairs that cover their bodies contain a toxin that can cause a serious allergic reaction. Add to that the fact that those hairs can sail right off the caterpillar like dandelion seeds, and you have an airborne allergen not unlike pollen.