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Heat hives, which are also known as cholinergic urticaria, are hives that occur as a reaction to an increase of body temperature. The hives usually appear as small red bumps, usually about the size of a mosquito bite. The rash may be in patches or all over the body. Sometimes, if the rash lingers, the bumps may join to form large irritated areas of skin. The exact cause of the condition is not completely understood, but some research has led to the conclusion that people who suffer the condition may be having an allergic reaction to their own body sweat.
People who experience these hives may have other symptoms as well. In some cases, the hives may cause itching or stinging. In severe cases, some people also may have breathing difficulties and experience a lowering of blood pressure. For some individuals, the appearance of this type of rash is believed to be a trigger for asthma attacks.
People who frequently experience heat hives should take precautions to keep their body temperature within normal range. For instance, they should probably exercise in an air conditioned room, and keep plenty of cold liquids on hand to help keep their body temperature from rising. When showering or bathing, water temperature should be cool or warm. When heat exposure is unavoidable, people who suffer from heat hives should be sure they are dressed appropriately. Ideally, in these circumstances, clothing should be loose and designed for hot weather.
In some instances, heat hives can also be brought about by stress, anger, and depression. Since emotion does not generally cause sweat, the link between emotional response and heat hives is unclear. One of the reasons that research has not led to a definitive cause of heat related hives may be because the triggers for the condition can greatly vary.
In order to diagnose heat hives, doctors usually conduct skin allergy tests. This is done by applying a chemical called methacholine to a small area of the skin. Methacholine is believed to duplicate the allergic reaction that people typically have to heat. Though this type of testing is typical, the results are only accurate about 33% of the time.
Treatment for people who suffer from heat hives usually consists of antihistamines or steroids. Antihistamine is a type of allergy medication that inhibits the production of a chemical called histamine, which is believed to be responsible for allergic reactions. Steroid treatment is usually reserved for chronic conditions or for those who experience some of the more severe symptoms associated with heat hives.