Am I Allergic to Exercise?
In patients with chronic urticaria, modest amounts of heat will cause mast cells to release histamine and other chemicals, resulting in hives and swelling. Ostro says this disruption of the mast cells, and an increased tendency for this to occur, are in fact, the underlying causes of chronic urticaria.
How to Treat?
Avoidance is the best treatment for cholinergic hives, but that may be difficult in warm weather or when exercising. “CU can usually be prevented by daily administering a long-acting, non-sedating antihistamine, such as cetirizine [Zyrtec or Reactine],” says Ostro.
If a rash does appear, it helps to cool the area promptly. “Ice cubes are the best,” says Kavanagh, “but I’m happy with cold water. Water is my best ally because wherever I am, water is fairly accessible.”
The Sweat Question
While this type of reaction is usually cholinergic urticaria, Ostro allows that two studies have implied – not proved – that there may be an allergy to one of the components of sweat in a rare group of individuals. Still, there is little to support an actual “allergy to sweat” in medical case studies.
“Though this mechanism may be operating in a few individuals, researchers who study CU attribute the majority of cases to an abnormal response of the nervous system called the cholinergic nervous system,” he says.
Perspiration, however, can assist a breakout of contact dermatitis, by releasing allergens from clothing or towels or adding to dermatitis irritation. But to be clear: the sweat itself does not cause such hives.
Ostro stresses that cholinergic urticaria is “not a form of contact dermatitis.” Contact dermatitis doesn’t develop immediately, “but takes 48 hours after contact with the inciting substance before skin lesions develop.” Those welts also take days to resolve, not minutes or an hour as is usually seen with CU.
The heat-triggered cholinergic urticaria is one of the physical urticarias, which also include reactions to cold, sun, even (in rare instances) water. It is also the only form of hives that can be sparked by emotions, such as anger.
It’s important to note a separate and dangerous form of exertion reaction: exercise-induced anaphylaxis or EIAn. This is a condition in which anaphylaxis, the most severe form of allergic reaction, results when a susceptible person exercises. It can also occur during strenuous chores, such as shoveling snow.
Unlike cholinergic urticaria, EIAn is only triggered by exercise, not heat stimuli. The reaction starts within minutes of exercise with flushing, itching and half-inch or larger hives (unlike cholinergic urticaria’s tiny hives). If exercising continues, the reaction can progress to anaphylaxis with swelling (face, throat, fingers, toes), nausea, abdominal cramps, diarrhea and loss of blood pressure.