What are Hives and Heat Rash?

Symptoms and Treatment of Cholinergic Urticaria

Cholinergic urticaria is caused by excessive heat exposure.

People who have a physical urticaria have a physical trigger for their hives, such as pressure, scratching, heat, cold, sunlight, water, or exercise. 

One common type of physical urticaria is cholinergic urticaria, also known as heat urticaria or heat rash. 

Definition of Cholinergic Urticaria

Cholinergic or heat urticaria is a form of chronic hives that is caused by an increase in body temperature such as hot showers, exercise, spicy foods, or being under too many covers in bed at night.

Strong emotions may also cause hives to occur in people with cholinergic urticaria.

The hives in cholinergic urticaria are classically pinpoint in size, less than the size of a mosquito bite and are itchy and red in color. They may group together, or coalesce, into larger hives over time. Occasionally, cholinergic urticaria can be associated with more severe symptoms, including asthma symptoms and low blood pressure.

It is important to differentiate exercise-induced anaphylaxis, which is a severe allergic reaction associated with exercise, from cholinergic urticaria. A key distinguisher is that people with cholinergic urticaria will often have hives with any increase in body temperature, such as with a hot bath, not just exercise.

It is not completely known why cholinergic urticaria occurs, although some people with this condition appear to have an allergy to their own sweat. This is determined by performing skin testing to a person’s own sweat.

Diagnosis of  Cholinergic Urticaria

A person’s symptoms, along with triggers that increase body temperature, are suggestive of cholinergic urticaria. That being said, it may be necessary to do various testing to confirm a true diagnosis. Some physicians will perform skin testing to methacholine, a chemical that may cause a positive test in people with cholinergic urticaria.

Unfortunately, this test is only positive in about one-third of those who suffer from this syndrome.

Other testing includes any method to increase a person’s body temperature, including exercising and a hot water bath. These tests are only rarely done in most clinical settings—you can imagine it is difficult to replicate a hot bath in your doctor's office. With that, a diagnosis is usually made by a person’s history of symptoms.

Treatment of Cholinergic Urticaria 

The best treatment for cholinergic urticaria is antihistamines. While any antihistamine is likely to be helpful, older antihistamines, such as hydroxyzine, seem to work especially well.

Severe cases of cholinergic urticaria have been successfully treated with danazol, which is an anabolic steroid. Use of this medication is limited by its severe side effects, however.

Other people with cholinergic urticaria respond well to beta-blockers, especially when strong emotions seem to be a cause of a person’s symptoms. These medications should be used with caution in people who actually may have exercise-induced anaphylaxis, however.

 

A Word From Verywell

Research suggests that cholinergic urticaria is the second most common type of physical urticaria, following dermatographism—a type of physical urticaria  that causes hives to form on the skin when exposed to pressure or scratching.

While unpleasant for the person experiencing it, the good news is that cholinergic urticaria is a much less concerning syndrome than exercise-induced anaphylaxis, and it can be managed well with trigger avoidance and oral antihistamines. 

Sources:

Alsamarai AM, Hasan AA, Alobaidi AH. Evaluation fo different combined regimens in the treatment of cholinergic urticaria. World Allergy Organ J. 2012 Aug;5(8):88-93.

Montogomery SL. Cholinergic urticaria and exercise-induced anaphylaxis. Curr Sports Med Rep. 2015 Jan;14(1):61-3.

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