"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.
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.
"I think most people, when they think of anaphylaxis or allergic reactions, they're thinking about insects like wasps and bees," said John Klotz, an entomologist at the University of California, Riverside. But these caterpillars exemplify the range of creatures out there that don't need to sting you to cause a reaction.
Klotz is publishing a review of reports on dozens of animals and insects, including the hairy caterpillars, that can cause a severe allergic response.
"I thought it would be a good way of heightening awareness of the problem," he said.
Deemed as forest pests in Europe, the processionary caterpillars -- named as such because they form long lines when heading into or out of their nests -- have been implicated in numerous individual and group incidents.
In June 2004, more than 40 people who were sitting under an infested oak tree in the region of Saarland in Southwest Germany were sickened by the caterpillars although only a few actually touched them.
"Someone could inhale them [the hairs] or ingest them, and in some cases they could penetrate the skin," said Klotz. Some children have been hospitalized after eating the creatures. "A lot of times they'll pick up something furry and curious like a caterpillar, and you know, sometimes ingest them, just out of curiosity."