Heat Rash in Adults - Why It Happens and How to Treat It

What Causes Heat Rash

Heat rash (miliaria) occurs when sweat ducts become blocked, trapping perspiration beneath the skin. The trapped sweat causes inflammation, resulting in small bumps, itching, and discomfort. While commonly associated with infants, adults frequently develop heat rash during hot weather, intense exercise, or when wearing occlusive clothing.

Three types exist: miliaria crystallina (superficial, clear blisters), miliaria rubra (deeper, red itchy bumps - the most common), and miliaria profunda (deep, flesh-colored bumps that can impair sweating). Each represents blockage at a different depth within the sweat duct.

Risk Factors and Triggers

Anything that promotes sweating while preventing evaporation increases risk: humid climates, synthetic fabrics, heavy creams or ointments that occlude pores, prolonged bed rest, and intense physical activity. Skin folds (under breasts, groin, armpits) are particularly susceptible due to friction and trapped moisture.

Treatment

The primary treatment is cooling the skin and allowing sweat ducts to clear. Move to a cool environment, remove occlusive clothing, and allow affected areas to air dry. Calamine lotion or hydrocortisone cream (1%) reduces itching. Avoid heavy moisturizers on affected areas as they can worsen duct blockage. Most cases resolve within days once the triggering conditions are removed.

Prevention

Wear loose, breathable fabrics (cotton, moisture-wicking synthetics). Avoid heavy creams in hot weather. Shower promptly after sweating and dry skin thoroughly. Use fans or air conditioning to reduce ambient temperature. In humid climates, lightweight powder in skin folds can absorb excess moisture and reduce friction.