Anaphylaxis is a severe, potentially life-threatening allergic reaction, typically associated with triggers like foods, insect stings, or medications. In a small number of cases, vigorous physical exertion can trigger this severe immune response, a condition known as exercise-induced anaphylaxis (EIA).
Defining Exercise-Induced Anaphylaxis
EIA is a distinct medical syndrome where physical activity brings on a systemic allergic reaction. The reaction involves the rapid release of chemical mediators, such as histamine and tryptase, from mast cells and basophils throughout the body. This sudden release of chemicals leads to a cascade of symptoms affecting the skin, airways, and circulation.
The mechanism for EIA is not fully understood, but exercise appears to lower the threshold required for these immune cells to degranulate. Unlike localized reactions, EIA is a whole-body event that can lead to vascular collapse. For many individuals, the reaction requires the presence of a co-factor, such as having eaten a specific food beforehand.
How Often Does EIA Occur
EIA is considered a rare disorder, and exact figures are difficult to determine due to underreporting and potential misdiagnosis. Population studies estimate the frequency of EIA to be approximately 0.031% in adolescents, with other data suggesting a prevalence between 50 and 2,000 episodes per 100,000 people per year.
Exercise is thought to be the trigger in approximately 5% to 15% of all anaphylaxis cases. A significant portion of these are the food-dependent subtype (FDEIA), where food ingestion must precede physical activity. This subtype accounts for roughly one-third to one-half of all EIA patients.
The condition often begins during adolescence or early adulthood, though cases have been reported across a wide age range. Some studies show a two-to-one female predominance.
Common Triggers and Warning Signs
The most common cause of EIA involves a co-factor, meaning neither the exercise nor the co-factor alone will trigger the reaction. The most frequently identified co-factor is a specific food consumed within a few hours of physical activity (FDEIA). Common trigger foods include wheat, shellfish, tomatoes, and peanuts.
Non-steroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen, are another important co-factor. Other factors that can lower the reaction threshold include alcohol consumption, temperature extremes, high humidity, and hormonal changes related to the menstrual cycle. The reaction typically starts within 30 minutes of beginning physical exertion, but can occur at any point during or shortly after the activity.
The first warning signs often include fatigue, generalized itching, or a warm sensation spreading across the body. This is followed by widespread flushing, hives (urticaria), and swelling beneath the skin (angioedema). More severe symptoms can quickly develop, involving shortness of breath, wheezing, nausea, vomiting, and cardiovascular collapse leading to lightheadedness and fainting.
Immediate Treatment and Prevention Strategies
During an acute EIA episode, the first step is to stop exercising immediately and rest, ideally lying down with the feet elevated to maintain blood flow. If symptoms progress beyond mild skin issues, the primary treatment is the immediate intramuscular injection of epinephrine, typically delivered via an auto-injector. Early administration of epinephrine is associated with better outcomes, and emergency medical services should be called immediately after the injection.
Long-term management focuses on individualized prevention strategies based on identified co-factors. For those with FDEIA, the standard recommendation is to avoid the trigger food for four to six hours before physical activity. Individuals should also avoid taking NSAIDs or alcohol for several hours before exercise if they are known co-factors.
Safety measures include exercising with a partner who knows how to use the epinephrine auto-injector and wearing medical identification. Patients should work with an allergist to develop a comprehensive emergency action plan and understand the specific intensity or type of exercise that may trigger their reaction.