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What Causes Prickly Heat Rash?

Prickly heat rash, also known as sweat rash and miliaria, is a condition characterized by small red bumps on the skin. These bumps tend to be itchy and uncomfortable. They sometimes cause a prickly pins-and-needles sensation, which is how the condition got its name. Prickly heat rashes are always caused by sweat, but certain causative factors are usually also present.

  1. Intense Exercise

    • When you are exercising strenuously, the body sweats a lot. The large amount of sweat being produced can overwhelm the sweat glands, causing them to become blocked. Sweat isn't able to get out of the body properly and builds up, irritating the skin. A heat rash develops soon afterward. This is especially true if you are exercising in warm, humid weather.

    Thick Creams and Ointments

    • Some creams and ointments are very thick, which stops air from getting to the skin. Sweat starts evaporating when the air hits it, but the creams prevent evaporation and trap the sweat. Irritation and a heat rash result. This is especially true of antiperspirants. Antiperspirants don't actually stop the body from sweating. They simply trap the sweat. Insoluble creams and gels such as petroleum jelly also have this effect.

    Tight Clothing

    • Tight clothing has an effect similar to that of thick creams. It prevents oxygenation and forces sweat to stay in place for long periods of time. Common offenders include spandex and leather, but any type of clothing can cause a heat rash if worn too tight. Wearing too many layers of clothing, even if they're not tight, can cause a heat rash as well, so you can develop prickly heat rash even in the winter.

    Other Causes

    • There are some less common causes of heat rash. One is primary hyperhidrosis. Primary hyperhidrosis is a condition in which the body sweats excessively, often causing recurring heat rashes. Some medications may cause heat rashes due to increased sweating. Immobility can also cause heat rashes -- for example, a person lying on his back for a long period of time can get a heat rash on his back.

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