CausesBy Mayo Clinic staff
Heat 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 that enhance sweat gland function may contribute to heat rash, including clonidine (Catapres, Duraclon, others), beta blockers and opiates.
- 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.
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- Gibson LE (expert opinion). Mayo Clinic, Rochester, Minn. Dec. 22, 2011.