Heat Rash: Symptoms, Relief and Prevention

Heat rash develops when sweat becomes trapped beneath the skin, causing small bumps, irritation or a prickling sensation.

Also called miliaria, prickly heat or sweat rash, it often appears in hot, humid conditions or where clothing and skin folds hold warmth. Several forms exist depending on how deeply a sweat duct is blocked, so the rash may look clear, red or more inflamed.

Heat rash very commonly presents as a cluster of tiny skin bumps. Skin redness, itching, stinging or a prickly feeling can accompany the rash, especially during sweating. Some bumps look clear and superficial, while deeper inflammation can produce firmer, sore bumps.

Common sites include the neck, upper chest, back, groin, under the breasts, armpits and areas covered by snug clothing. In babies, covered areas and skin folds may be affected.

A sweat duct can become obstructed as the skin stays hot and damp. Sweat then leaks into nearby skin instead of reaching the surface normally, triggering bumps and inflammation. Heavy sweating, friction, occlusive creams, dressings and fabrics that restrict evaporation can contribute.

People with hyperhidrosis produce excessive sweat and may have more opportunity for moisture to collect, but heat rash can occur without that condition.

Mild heat rash often settles after the skin is cooled and kept dry, though the bumps may take several days to fade. Continued heat and sweating can maintain the blockage or trigger new areas. Deeper forms can last longer and may interfere with normal sweating, making heat exposure harder to tolerate.

Hot, humid weather, intense exercise, fever and prolonged bed rest can keep skin warm and sweaty. Tight or non-breathable clothes, heavy bedding and covered skin folds reduce ventilation. Babies are particularly susceptible because their sweat ducts are still developing, while anyone newly exposed to a much hotter climate may also notice a rash.

A clinician usually identifies heat rash from its appearance, location and link with heat or sweating. They may ask about new medicines, products, clothing, fever and recent environmental exposure because contact dermatitis, folliculitis, infection and other rashes can resemble it.

Testing is not routinely needed for a straightforward presentation. An examination becomes more useful when bumps are painful, widespread, repeatedly returning or not improving after cooling measures.

Move to a cooler, ventilated place, loosen clothing and let the affected skin dry. A cool shower or compress can ease discomfort; pat rather than rub afterward. Lightweight, breathable garments reduce friction and help sweat evaporate.

Avoid thick ointments or oily products that may further block sweat ducts. A clinician may recommend a suitable soothing product, emollient or short course of topical corticosteroid when inflammation is troublesome, depending on the rash and body site. Do not apply a steroid to a baby, the face, broken skin or a skin fold unless a qualified clinician has advised the exact product and method.

Plan strenuous tasks for cooler parts of the day and use air conditioning or a fan where available. Change damp clothes promptly, keep bedding light and choose fragrance-free skin products if the area feels sensitive. Try not to scratch; trimmed nails and a cool compress can reduce accidental skin damage.

Scratched or persistently damp skin can become infected. Arrange medical assessment for increasing pain, warmth, swelling, pus, fever or redness that is spreading beyond the original area. Urgent help is needed for confusion, fainting, severe weakness or other signs of heat illness; these symptoms reflect overheating rather than a simple skin rash.

Choose loose, breathable clothing and avoid heavy layers in warm conditions. Keep living and sleeping spaces cool, allow skin folds to dry, and take regular breaks during exercise or outdoor work. Use skin products with a light texture when possible, particularly on areas that become sweaty or occluded.

A GP or dermatologist can distinguish persistent heat rash from eczema, contact reactions, folliculitis and infection. Seek advice if the rash keeps returning, covers a large area, affects a baby and is not settling, or makes sweating difficult. Bring details of recent products, medicines, activities and heat exposure to make the assessment more precise.