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Causes
By Mayo Clinic staffHeat rash develops when some of your sweat ducts become clogged. Instead of evaporating, perspiration remains trapped beneath the skin, causing inflammation and rash.
It's not always clear why the sweat ducts become blocked, but certain factors seem to play a role, including:
- Immature sweat ducts. Because a newborn's sweat ducts aren't fully developed, they can rupture more easily, trapping perspiration beneath the skin. This usually happens in hot weather, but can occur anytime infants are dressed too warmly. Newborns who have high fevers or are in incubators can also develop blocked sweat ducts.
- Tropical climates. Hot, humid weather is particularly conducive to miliaria.
- Physical activity. Intense exercise, hard work or any activity that causes you to perspire extensively can lead to heat rash.
- Certain fabrics. You may develop heat rash if you consistently wear clothing that doesn't allow perspiration to evaporate normally.
- Medications. Certain prescription medications have been linked to heat rash, including bethanechol (Urecholine), which treats bladder problems; clonidine (Catapres), a high blood pressure drug sometimes used to treat attention-deficit/hyperactivity disorder (ADHD); the acne medication isotretinoin (Accutane); and doxorubicin (Adriamycin), a chemotherapy drug.
- Overheating. Overheating in general — bundling up too much in winter, sleeping under an electric blanket — can lead to heat rash.
- Heavy creams and ointments. These products can block the sweat ducts.
Heat rash can also occur in people who are confined to a hospital bed for long periods, especially if they have a fever.
References
- Pielop JA. Benign skin and scalp lesions in the newborn and young infant. http://www.uptodate.com/home/index.html. Accessed Nov. 12, 2009.
- Miliaria. The Merck Manuals: The Merck Manual for HealthCare Professionals. http://www.merck.com/mmpe/print/sec10/ch118/ch118e.html. Accessed Nov. 2, 2009.
- Acne, rosacea and related disorders. In: Habif TF. Clinical Dermatology. 5th ed. Maryland Heights, Mo.: Mosby; 2009. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-7234-3541-9..00016-X--s0970&uniq=174064897&isbn=978-0-7234-3541-9&sid=924617043#lpState=open&lpTab=contentsTab&content=4-u1.0-B978-0-7234-3541-9..00016-X--s0975%3Bfrom%3Dcontent%3Bisbn%3D978-0-7234-3541-9%3Btype%3DbookPage. Accessed Dec. 2, 2009.
- Extreme heat: A prevention guide to promote your personal health and safety. Centers for Disease Control and Prevention. http://www.bt.cdc.gov/disasters/extremeheat/heat_guide.asp. Accessed Nov. 1, 2009.
- Fealey RD, et al. Disorders of the eccrine sweat glands and sweating. In: Wolff K, et al. Fitzpatrick's Dermatology in General Medicine. 7th ed. New York, N.Y.; McGraw-Hill Companies; 2008. http://www.accessmedicine.com/content.aspx?aID=2985825. Accessed Dec. 2, 2009.
- Walker JS, et al. Heat emergencies. In: Tintinalli JE, et al. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York, N.Y.: McGraw-Hill Companies; 2004. http://www.accessmedicine.com/content.aspx?aID=604435. Accessed Dec. 2, 2009.
- Godkar D. Rare skin disorder complicating doxorubicin therapy: Miliaria crystallina. American Journal of Therapeutics. 2005;12:275.
- Berger TG. Dermatologic disorders. In: McPhee SJ, et al. Current Medical Diagnosis and Treatment 2010. New York, N.Y.: McGraw-Hill Companies; 2010. http://www.accessmedicine.com/content.aspx?aID=747. Accessed Dec. 2, 2009.
- Seto CK, et al. Environmental illness in athletes. Clinics in Sports Medicine. 2005;24:695.
- Gibson LE (expert opinion). Mayo Clinic, Rochester, Minn. Dec. 9, 2009.
