Cause Heat rash is caused by blocked-off sweat glands. Lots of children get it during hot, humid weather when sweat glands are overworked.
Older children can get it with exercise.
Expected Course With treatment, heat rash usually clears up completely in 2 to 3 days. Home Care Cooling. Give cool baths every 2 to 3 hours, without soap. Let the skin air-dry. For localized rashes, apply a cool, wet washcloth to the area for 5 to 10 minutes.