Heat Rash (Prickly Heat)

What heat rash looks like

Heat rash comes in types depending on how deep the blockage in the sweat duct is:

On darker skin, the redness may be less obvious, and bumps may look skin-colored, gray or slightly darker.

Causes and risk factors

Sweat ducts become blocked, so sweat cannot reach the surface and leaks into surrounding tissue, causing inflammation. Triggers include:

• Hot, humid weather
• Overdressing, especially babies wrapped too warmly
• Tight, non-breathable clothing and heavy bedding
• Intense exercise or physical work
• Fever and bed rest, particularly lying on the back for long periods
• Heavy creams and ointments that block sweat ducts
• Newborns, whose sweat ducts are still developing
• Travel to tropical climates
• Some medicines that increase sweating

Heat rash in babies

Heat rash is very common in newborns and infants, often on the neck, shoulders, chest, armpits, elbow creases and diaper area. Babies may be fussy. Dress them in light, loose layers, keep the room comfortably cool, and avoid heavy creams. Most baby heat rash clears quickly once the baby is cooler. A rash with fever, poor feeding or unusual sleepiness needs a doctor's assessment. See diaper rash for rashes confined to the diaper area.

Heat rash vs other rashes

Diagnosis

A doctor diagnoses heat rash by looking at it and asking about heat exposure, clothing and activity. Tests are rarely needed. A swab may be taken if infection is suspected.

Treatment and home care

• Cool down: move to a cool, shaded or air-conditioned place. Use a fan.
• Cool showers or baths, then let the skin air-dry rather than rubbing it.
• Loose, light cotton clothing, and remove extra layers from babies.
• Avoid heavy creams, oils and ointments, which can block sweat ducts further.
• Ease itch: calamine lotion, cool compresses, or a mild over-the-counter hydrocortisone cream for a few days in adults and older children. Ask a doctor before using hydrocortisone on babies.
• Avoid scratching, which can cause infection. Keep children's nails short.
• Antihistamines may help adults sleep if itch is severe. Follow the label dose.
• Infected heat rash may need antibiotics.

Most heat rash clears within 2 to 4 days once the skin is kept cool.

Prevention

• Wear loose, breathable clothing in hot weather.
• Avoid overheating, especially during exercise. Take breaks in the shade or air conditioning.
• Dress babies in the same number of layers you would wear, or one extra layer at most.
• Use light, water-based moisturizers and sunscreens rather than heavy ones.
• Shower after sweating heavily.
• Stay hydrated.

Frequently asked questions

What does heat rash look like?

Heat rash usually looks like clusters of tiny red bumps or small clear blisters, often on the neck, chest, back, armpits or groin. It may feel prickly, stinging or itchy. On darker skin, the bumps may look skin-colored or slightly darker rather than red.

How long does heat rash last?

Most heat rash clears within 2 to 4 days once the skin is cooled and sweating reduced. It can return with more heat. A rash that lasts longer than 3 to 4 days despite cooling, or that becomes painful or pus-filled, should be checked by a doctor.

How do you get rid of heat rash fast?

Cool the skin quickly with a cool shower or fan, wear loose cotton clothing, avoid heavy creams and let the skin dry naturally. Calamine lotion or cool compresses ease itching. Most rashes improve within hours to a few days.

Is heat rash dangerous?

Heat rash itself is usually harmless. However, it shows the body is overheating. If someone with heat rash becomes dizzy, confused, nauseated or stops sweating, they may have heat exhaustion or heat stroke, which need urgent cooling and medical care.

What is the difference between heat rash and hives?

Heat rash is made of tiny bumps or blisters where sweat collects and appears with heat. Hives are larger, raised, itchy welts that can appear anywhere, change shape and move around within hours, often due to an allergic reaction, infection or other triggers.