Slide show: Poison ivy and other summer skin irritants
Photos of heat rash
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Heat rash develops when the sweat ducts become blocked and perspiration is trapped under your skin. Miliaria rubra (A), one type of heat rash, appears as red clusters of small blister-like bumps that can produce a stinging sensation. Miliaria crystallina (B), another type of heat rash, appears as clear, fluid-filled bumps that produce no other signs or symptoms. Heat rash is most common in skin folds and wherever clothing causes friction.

Heat rash isn't serious and usually resolves quickly when the affected area cools. In the meantime, reduce sweating by staying in an air-conditioned space or using fans to circulate the air. Wear lightweight clothing and limit physical activity.

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