Exercise-induced anaphylaxis (EIA) is a rare but potentially life-threatening allergic reaction triggered by physical activity. While most people experience only muscle fatigue or shortness of breath during exertion, a small subset of individuals can develop a severe systemic allergic response. This condition is a multi-system disorder that requires immediate medical attention, as it is not merely an overreaction to heat or exertion. EIA is estimated to account for 5% to 15% of all documented anaphylaxis cases. Understanding its signs and triggers is important for anyone who experiences unusual symptoms while being physically active.
Defining Exercise-Induced Anaphylaxis (EIA)
EIA is defined as a systemic hypersensitivity reaction that occurs only during or shortly after physical exertion. The unique trigger is exercise itself, often moderate to vigorous activities like jogging or cycling. The reaction stems from the degranulation of mast cells, which release potent chemical mediators, such as histamine, into the bloodstream. This release causes tissues to swell and blood vessels to dilate, leading to the systemic symptoms characteristic of anaphylaxis. EIA is a systemic event that affects multiple organ systems and can progress rapidly to severe cardiovascular involvement, distinguishing it from localized conditions like exercise-induced asthma or cholinergic urticaria.
Recognizing the Signs
Symptoms typically begin within minutes of starting exercise, often within the first 30 minutes, or shortly after stopping. Initial signs are often mild, affecting the skin with generalized itching (pruritus), flushing, or warmth. As the reaction progresses, skin manifestations become pronounced, presenting as large, raised, itchy welts (urticaria or hives). Swelling beneath the skin (angioedema) may affect the face, lips, tongue, or throat, potentially leading to breathing difficulty, and may be accompanied by gastrointestinal symptoms like nausea or cramping. The reaction becomes life-threatening when it affects the respiratory or cardiovascular systems, causing wheezing, throat constriction, or a rapid drop in blood pressure (hypotension) that can lead to shock.
Identifying Specific Triggers
Exercise is the unifying trigger, but EIA is frequently a co-factor dependent condition, meaning physical activity alone may not provoke an episode. The most common subtype is Food-Dependent Exercise-Induced Anaphylaxis (FDEIA). In FDEIA, a reaction only occurs if a specific allergenic food is consumed within 4 to 6 hours before exercise. The food or the exercise alone can be tolerated without symptoms, but the combination triggers mast cell release. Common food triggers include:
- Wheat (especially the omega-5 gliadin protein)
- Shellfish
- Peanuts
- Tree nuts
Medication and Environmental Factors
Another co-factor involves non-steroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen. Taking these medications close to exercise can facilitate the reaction, often called “summation anaphylaxis.” NSAIDs are believed to contribute by increasing the permeability of the intestinal lining. Other environmental and physiological factors can also lower the reaction threshold, such as extremes in temperature and humidity, hormonal changes, and acute infections. In some cases, known as Idiopathic EIA, no specific co-factor is identified, and exercise appears to be the sole trigger.
Immediate Management and Prevention
Immediate management involves a rapid response to prevent the reaction from progressing. The first action is to stop exercising immediately and rest, regardless of initial symptom severity, as continuing physical activity worsens the systemic reaction. The only medication that reverses anaphylaxis progression is epinephrine, administered via an auto-injector (EpiPen). Anyone diagnosed with EIA or FDEIA is typically prescribed two auto-injectors and should carry them at all times. After administering epinephrine, or if symptoms escalate rapidly, emergency medical services must be called immediately.
Long-Term Prevention
Long-term prevention focuses on avoiding identified triggers and co-factors. Individuals with FDEIA must strictly avoid the specific allergenic food for 4 to 6 hours before any physical activity. Similarly, co-factor medications, like NSAIDs, should be avoided entirely before exercise. Additional preventative measures include exercising with a partner aware of the condition and knowing how to use the auto-injector. Patients may also need to modify their exercise routine by reducing intensity or changing the type of activity that reliably triggers a reaction. Wearing medical identification, such as a bracelet, informs first responders of the condition in an emergency.