Sometimes at the gym, you’ll hear tales of a runner who’s “allergic to their own sweat.” Chances are, it’s not the perspiration – it’s the heating up of the body through exercise that’s causing the person to break out in a rash.
This is what’s known as cholinergic urticaria or hives. The condition can be triggered by several heat-raising activities: jogging or aerobic workouts are obvious, but also hot baths or showers, eating spicy foods, and even emotional stress can bring on the hives.
Lise Kavanagh’s body reacts with hives to the physical stimulus of heat. “Some of my worst attacks happen when I’m sleeping. Even if I have no blankets at all, when I stir in the night and end up on my back, the heat accumulates between the mattress and my skin, and I’ll wake up with a rash all over my back.”
While a relatively rare condition, experts say that 5 per cent of people who have chronic urticaria (hives) also experience the cholinergic symptoms. In the United States, it’s estimated that one in five people will experience chronic urticaria in their lifetime.
Spotting the Condition
With cholinergic urticaria or CU, the hives are tiny, about the size of a ball point pen tip. The rash comes on rapidly, usually within a few minutes of perspiring, and can last from 30 minutes to an hour or more before receding once the body returns to normal temperature.
The hives or “wheals” are very itchy, and can be preceded by a burning, tingling and/or warm sensation.
The wheals may join to form a large mass of swelling, and some people also experience headaches, salivation, palpitations, fainting, shortness of breath, abdominal cramps and diarrhea.
“CU appears when the affected individual’s body is heated by exertion or a situation that raises the core temperature of the body 2.7 degrees F or more,” says Dr. Martin Ostro, an allergist with the division of allergy and immunology at Massachusetts General Hospital in Boston.
Technically, it’s not an actual allergy since cholingeric urticaria has no specific IgE, the allergic antibody, created to respond to a particular substance. But the mechanism of the reaction is similar to allergy.
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],” 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.”
While a reaction to perspiration 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.
There’s a sub-type of EIAn that only occurs when exercising within two to four hours after eating a specific food. The individual can exercise without symptoms, as long as the incriminated food is not consumed beforehand. Likewise, the person can eat that food with no reactions as long as no exertion follows for more than four hours after eating the food.
This condition, known as Food-Dependent EIAn, is challenging to diagnose. If you suspect symptoms of this, be sure to see an allergist for testing.
In fact, Ostro recommends that individuals who start to experience flushing, itching or hives during exercise immediately stop the activity, and consult an allergist before resuming a workout regime. When EIAn is diagnosed, the person will be prescribed an epinephrine auto-injector.
“Cholingeric urticaria is bothersome but non-life threatening, while EIAn is a potentially life-threatening condition,” Ostro says. Fortunately, the former condition is the more prevalent.
Is Exercise Possible?
So can the person with cholingeric urticaria hives stay fit and exercise? Yes, but it may involve finding a less heat-inducing sport such as swimming, or inclining to winter sports such as skiing.
Kavanagh, who lives in New Brunswick, Canada, enjoys both. But she doesn’t limit herself to them. She races dirt bikes and rappels off mountains, too. She just ensures that she takes appropriate safeguards to avoid and minimize her body heat reactions.
Besides staying out of direct sunlight and taking medication, Kavanagh layers her clothing for temperature changes, and wears a “cold” shirt that wicks away sweat while maintaining her active lifestyle. “I refuse to let my allergy get the best of me.”