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Histamines are released by the immune system as a way to fight off or protect your body from harmful or potentially harmful stimuli. Excessive body heat can be harmful to the body, and when you exercise, your body heat rises. As this occurs, your immune system releases histamines that protect your body from the heat and may cause swelling or redness on particular parts of your body. This histamine release is often referred to as little red dots; MayoClinic.com calls this phenomenon a heat rash or malaria and cholinergic urticaria 12.
A heat rash can develop on the body whenever the core body temperature rises. This can occur during or after exercise because your sweat ducts become blocked and perspiration traps under your skin. If your skin is hypersensitive to temperature change, transitioning from a cold environment to a warmer environment can cause stress to your body and a heat rash may be the result. Exercise can cause a heat rash because the body quickly changes temperatures.
The histamine response from the heat rash may range from little red dots to small or larger blistery red lumps. The most common symptom of a heat rash is that the dots or lumps may itch or feel prickly under the skin. Red dots or lumps may appear in skin folds around the armpits, under the knees, below the neck, groin, and arm fold. MayoClinic.com states that a heat rash can also appear under clothes that rub against the skin 1. You can experience a heat rash during or after exercise.
A heat rash does not typically last very long and it usually goes away on its own. The best way to alleviate the symptoms of a heat rash is by allowing time for your skin to cool down. During this time, prevent your skin from sweating because sweating will cause your body temperature to cool down too rapidly. During exercise, wear clothing that is loose-fit and made of cotton. This will protect the body from heat rash by allowing air to flow through the clothes and help cool the body and keep it dry.
Severity and Duration of Heat Rash
A heat rash is rarely life threatening. Additionally, this condition can be highly variable and long-lasting — experiencing the rash for years can be harmless. You may be able to find treatment regimens that help you control the outbreaks and/or help you treat the rash from exercise. If you experience severe swelling in the areas where the rash forms, you should contact your doctor. In rare cases, a heat rash can cause anaphylactic shock and could be life threatening.
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