Exercise can trigger or worsen asthma or, rarely, a severe allergic (anaphylactic) reaction.
Doctors usually base the diagnosis on symptoms and their relationship to exercise.
Drugs used to treat asthma can usually prevent symptoms from developing during exercise, but becoming more physically fit and gradually increasing the intensity and duration of exercise also helps.
(See also Overview of Allergic Reactions Overview of Allergic Reactions Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance. Usually, allergies cause sneezing, watery and itchy eyes, a... read more 
.)
Exercise can trigger the following:
Asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more
: Exercise often triggers an asthma attack in people who have asthma, but some people have asthma only when they exercise. Exercise may trigger or worsen asthma because breathing fast cools and dries the airways, and as the airways warm again, they narrow. Exercise-induced asthma is more likely to occur when the air is cold and dry. The chest feels tight. People may wheeze, cough, and have difficulty breathing.Anaphylactic reactions Anaphylactic Reactions Anaphylactic reactions are sudden, widespread, potentially severe and life-threatening allergic reactions. Anaphylactic reactions often begin with a feeling of uneasiness, followed by tingling... read more : Rarely, vigorous exercise triggers a widespread, potentially severe allergic (anaphylactic) reaction. In some people, this reaction occurs only if they eat a specific food (especially wheat or shrimp) before exercising. Breathing becomes difficult or blood pressure falls, leading to dizziness and collapse. An anaphylactic reaction can be life threatening.
Typically, symptoms triggered by exercise—asthma or an anaphylactic reaction—occur after 5 to 10 minutes of vigorous exercise. Sometimes symptoms begin after exercise has stopped.
Diagnosis
A doctor's evaluation
Sometimes an exercise challenge test
The diagnosis of exercise-induced allergic reactions is based on the symptoms and their relationship to exercise.
An exercise challenge test Diagnosis can also help doctors make the diagnosis. For this test, lung function is measured before and after exercise on a treadmill or stationary bicycle.
Treatment
Drugs used to treat asthma or anaphylaxis
Avoidance of possible triggers
For people with exercise-induced asthma, the goal of treatment is to be able to exercise without symptoms. Becoming more physically fit may make symptoms less likely to develop during exercise. Inhaling a beta-adrenergic drug (such as those used to treat asthma Drugs Commonly Used to Treat Asthma 
) about 15 minutes before starting to exercise often helps prevent reactions. Cromolyn, usually taken through an inhaler, may be helpful.
For people with asthma, taking the drugs usually used to control asthma often prevents symptoms from developing during exercise. Taking drugs to treat asthma and gradually increasing the intensity and duration of exercise enables some people with asthma to tolerate exercise.
People who have had an exercise-induced anaphylactic reaction should avoid the form of exercise that triggered the attack. If eating a specific food before exercise triggers symptoms, they should not eat the food before exercise.
A self-injecting syringe of epinephrine should always be carried for prompt emergency treatment. Exercising with other people is recommended.
