Exercise-induced anaphylaxis and urticaria are rare allergic reactions triggered by activity in certain people. Exercise-induced anaphylaxis is a serious, potentially fatal allergic reaction brought on by exercise. The term anaphylaxis is used when two or more body systems are involved in an allergic reaction (for instance, wheezing and skin rash). The condition can progress to anaphylactic shock, which can involve difficulty breathing and a dangerous drop in blood pressure.

In some instances, exercise-induced anaphylaxis occurs after a person has consumed particular allergenic foods (e.g., fish, milk). In individuals who are susceptible to this condition, the exercise lowers a mechanism in the body known as the mast cell degranulation threshold. The result is the release of histamines and other allergy mediators that are responsible for causing an allergic reaction.

Exercise-induced anaphylaxis tends to affect young people (25 is the mean age of onset), women and those with a family history of atopy (genetic tendency toward allergies) more than other groups.

Exercise-induced urticaria can be a form of a condition known as cholinergic urticaria. Cholinergic urticaria occurs when passive or active warming of the body triggers hives – red, swollen patches of skin that occur in groups. The danger of exercise-induced urticaria usually is less acute than that of anaphylaxis. However, in extreme cases, exercise-induced urticaria can actually develop into anaphylaxis. Most often, exercise-induced urticaria tends to affect people in their middle to late 20s.

Though the danger of the two exercise-induced conditions differs dramatically, they are both allergic reactions that share the same pathway. As an antigen comes into contact with the body, the immune system mistakenly perceives it to be a harmful foreign substance. As part of the allergic reaction that follows, chemicals are released into the body, triggering symptoms.