What to know about severe or worsening heat rash

Heat rash develops when sweat becomes trapped beneath the skin. It often appears as clusters of small bumps with prickling, itching or redness in hot, humid conditions, particularly where clothing or skin folds hold heat and moisture.

More troublesome heat rash may cover a larger area, interrupt sleep, sting with sweating or become raw from rubbing and scratching. Common sites include the neck, upper chest, back, groin, beneath breasts, armpits and areas under tight clothing. In babies, covered skin and folds are particularly vulnerable.

Not every rash arising in hot weather is heat rash. Hives, contact dermatitis, fungal infection and bacterial follicle inflammation can resemble it. Blisters, marked tenderness, drainage or illness make a different or additional problem more concerning.

Move to an air-conditioned or shaded place, loosen clothing and let damp areas dry. A cool shower or cool compress can soothe prickling. Choose light, breathable fabric, pause strenuous activity in the heat and change out of sweaty clothes promptly.

Avoid scratching, heavy ointments and oily products that may further trap sweat. Use a gentle, fragrance-free cleanser and pat rather than rub. A pharmacist or clinician can advise whether a soothing lotion or short course of an anti-inflammatory product is suitable for the person's age, skin site and medical history.

Get prompt medical advice for increasing pain, warmth, swelling, pus, spreading redness, fever or tender lumps near the affected area. These changes can indicate infection rather than uncomplicated sweat blockage.

Seek urgent care if the person is confused, faints, cannot drink, has trouble breathing or remains very hot after moving somewhere cool. These are not routine features of heat rash and may accompany serious heat illness or an allergic reaction. A rash that persists despite cooling also deserves review to confirm the diagnosis.

Ask whether the appearance fits heat rash or another condition, whether broken skin is infected, and which product is safe for the affected body site. Mention recent medicines, new skincare, sun exposure, workplace heat, fever and anyone else with a similar rash.