Diseases & Conditions

Heat Rash

Heat rash — also known as prickly heat and miliaria — isn't just for babies. Though it's most common in infants, heat rash affects up to a third of adults living in tropical climates and can plague anyone during hot, humid weather.

Heat rash develops when your sweat ducts become blocked and perspiration is trapped under your skin. Symptoms range from superficial blisters to deep, red lumps. Some forms of heat rash can be intensely itchy or prickly.

Most often, heat rash goes away on its own. Severe forms of heat rash may need medical care, but the best way to relieve symptoms is to cool your skin and prevent sweating.

Heat rash usually heals on its own and doesn't require medical care. See your doctor if you or your child has symptoms that last longer than three or four days, the rash seems to be getting worse or there are signs of infection such as:

• Increased pain, swelling, redness or warmth around the affected area
• Pus draining from the lesions
• Swollen lymph nodes in the armpit, neck or groin
• A fever or chills

No tests are needed to diagnose heat rash; your doctor can determine the problem with a visual exam.

The best treatment for any form of heat rash is to reduce sweating by staying in air-conditioned buildings or, when that's not possible, using fans to circulate the air, wearing lightweight clothing made of fabrics that "breathe" and limiting physical activity. Once skin is cool, heat rash tends to clear quickly.

Mild heat rash doesn't require any other treatment, but more severe forms may need topical therapies to relieve discomfort and prevent complications. Topical treatments may include:

• Calamine lotion to soothe itching
• Anhydrous lanolin, which may help prevent duct blockage and stop new lesions from forming
• Topical steroids in the most serious cases

Some anecdotal evidence supports the use of oral vitamin C supplements to help relieve heat rash.