The environment is the chief source of allergens that may cause trouble during exercise. A person who suffers from allergic rhinitis may react after encountering ragweed when pollen counts are especially high. Another individual may suffer from hives after being exposed to algae while swimming in a lake.

Examples of airborne allergens include:

• Pollen
• Molds
• Dust
• Animal dander

Exercising outdoors exposes people to insects, thereby increasing the likelihood of an insect bite or sting occurring. Certain types of insects release venom through stings and bites that can cause anaphylaxis, a whole-body allergic reaction that is potentially life-threatening. Stinging insects include:

• Honeybees
• Yellow jackets
• Paper wasps
• Hornets
• Fire ants

It appears that eating certain foods prior to exercise may increase the likelihood of an allergic reaction in the life-threatening form known as exercise-induced anaphylaxis. For this reason, patients who have experienced any kind of exercise-induced allergy or anaphylactic symptoms should take careful note of what they had eaten prior to the episode. By avoiding or controlling the consumption of these foods in the future, patients can help avoid further reactions.

Contact dermatitis is an allergic reaction with a rash consisting of itchy, red, small papular vesicles (a pimple-like blister) that ooze and crust. It usually appears several days after exposure, making it harder to track down the allergen responsible. However, the rash location sometimes can offer clues.

Sources of contact dermatitis during exercise include:

• Vegetation, such as poison oak or poison ivy encountered while running in a field or on the beach
  
  
• Elastic, such as that found on waistbands of athletic shorts
  
  
• Rubber or dyes in athletic footwear
  
  
• Paratertiary-butylphenol formaldehyde resin, found in athletic tape used in sports such as football and hockey

Recent studies have shown that air pollution can have a significant effect on a person's lungs. Specifically, research suggests that certain pollutants can trigger bronchoconstriction (tightening in the airways) in sensitive individuals, making it more difficult to breathe. Depending on the area, exercising outside may bring a person into contact with air pollutants and increase the chance of severe bronchoconstriction occurring during an allergy or asthma attack.