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Hives and Heat Rash

Hives and Heat Rash

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Updated April 09, 2014

Updated April 09, 2014
Hives and Heat Rash

What is a Physical Urticaria?

People who have a physical urticaria have a physical trigger for their hives, such as pressure, heat, cold, sunlight, water or exercise. Up to 20 to 30 percent of people with chronic urticaria have a physical cause.

What is Cholinergic Urticaria?

Cholinergic or heat urticaria is a form of chronic hives that is caused by an increase in body temperature. Hives are caused by any 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 pin-point in size, less than the size of a mosquito bite. These 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 make sure a person does not have exercise-induced anaphylaxis, which is a severe allergic reaction associated with exercise. 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 of these people appear to have an allergy to their own sweat. This is determined by performing skin testing to a person’s own sweat.

How is Cholinergic Urticaria Diagnosed?

A person’s symptoms, along with triggers that increase body temperature, are suggestive of cholinergic urticaria. It may be necessary to do various testing to make a true diagnosis, however. 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, and a diagnosis is usually made by a person’s history of symptoms.

How is Cholinergic Urticaria Treated?

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 that actually may have exercise-induced anaphylaxis, however.

Want to keep learning? Find out about dermatographism.

Source: Dice, JP. Physical Urticaria. Immunol Allergy Clin N Am. 2004;24:225-246.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.

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