Yes, you can get hives from exercise, a condition known medically as exercise-induced urticaria. Urticaria is a common skin reaction characterized by the sudden appearance of raised, intensely itchy welts, or wheals, on the skin. These reactions occur in response to physiological changes that happen during physical activity. The hives are a visible sign of an underlying immune or nervous system response to the stress of exertion.
The Specific Types of Exercise-Triggered Urticaria
Exercise can trigger two distinct types of hive reactions. The first, and most frequent, is Cholinergic Urticaria (CU), which is caused by an increase in core body temperature. This reaction is not limited to exercise and can also be triggered by hot showers, fevers, or emotional stress. The hives are typically very small, appearing as tiny, pinpoint papules often surrounded by a red flare, and they cause intense itching.
The second type is Exercise-Induced Urticaria (EIU), which sometimes leads to the more serious Exercise-Induced Anaphylaxis (EIA). This condition is rarer and occurs only during or immediately following physical activity, regardless of the environmental temperature. A significant variant of EIA is often linked to co-factors, most notably specific foods eaten within a few hours before exercise. For people with this condition, consuming the trigger food alone or exercising alone causes no symptoms, but the combination results in a reaction.
The Physiological Mechanism Behind the Hives
The appearance of hives is due to the activation of specific immune cells called mast cells, which reside in the skin. Mast cells are packed with chemical mediators, most notably histamine, which they quickly release in a process called degranulation when triggered. This surge of histamine into the surrounding tissue causes the characteristic symptoms of an allergic reaction.
In the case of Cholinergic Urticaria, the rise in internal body temperature stimulates the nervous system. This leads to the release of acetylcholine, a neurotransmitter theorized to cause mast cells to degranulate and release histamine. The resulting localized release of histamine causes small blood vessels in the skin to dilate and leak fluid, leading to the formation of itchy, raised wheals.
For Exercise-Induced Anaphylaxis, the exact mechanism is less understood but also involves mast cell degranulation. It is thought that the physical stress of exercise, sometimes combined with a food allergen in the bloodstream, lowers the threshold for mast cell activation. The rapid redistribution of blood flow during exercise is also hypothesized to play a role. The extensive release of histamine and other mediators in this condition can lead to a systemic reaction affecting multiple organs.
Recognizing Symptoms and Identifying Severe Reactions
Initial symptoms typically begin shortly after starting physical activity, often within the first 30 minutes. A person may first feel a generalized warmth and intense itchiness, followed by the appearance of raised welts or patches on the skin. These wheals can be small and pinpoint, common with Cholinergic Urticaria, or larger and more widespread, often appearing on the chest, neck, and extremities. Simple exercise hives usually resolve on their own within 30 to 60 minutes once the physical activity has stopped and the body has cooled down.
A serious concern is the progression to Exercise-Induced Anaphylaxis, which involves symptoms extending beyond the skin. Warning signs of a systemic reaction include difficulty breathing, wheezing, or a tightness in the throat. Severe symptoms can also involve the digestive system, such as abdominal cramping, nausea, or vomiting. Progression may also include feeling dizzy, faint, or experiencing a rapid heart rate, which indicates a potentially life-threatening drop in blood pressure.
Strategies for Managing and Preventing Exercise Hives
For people who experience recurrent exercise hives, the first-line treatment often involves antihistamines. Non-drowsy, second-generation H1-blockers are commonly recommended and are most effective when taken prophylactically before exercise. If the hives are due to Cholinergic Urticaria, environmental adjustments can significantly reduce the risk of a reaction. This includes exercising during cooler times of the day, opting for air-conditioned spaces, and wearing loose, moisture-wicking clothing to help manage body temperature.
Managing the more severe Exercise-Induced Anaphylaxis requires stricter behavioral modifications and medical oversight. Individuals with a suspected food co-factor should work with a specialist to identify and strictly avoid that food for four to six hours before any physical exertion. A medical professional may also advise against taking nonsteroidal anti-inflammatory drugs (NSAIDs) before a workout, as these medications can worsen a food-related anaphylactic reaction. Anyone diagnosed with or suspected of having EIA should be prescribed an epinephrine auto-injector and must always carry it during exercise.