Sweat rash under the armpits

Can sweat cause a rash on your armpits?

Yes. Heat rash, also called prickly heat or miliaria, develops when the tiny ducts that carry sweat to the skin surface become blocked. Trapped sweat causes inflammation, itching and small bumps or blisters. Armpits are a common location because skin touches skin and clothing covers the area. Heat and humidity increase the risk, but overdressing in cool weather can cause heat rash too.1

Sweating is how your body cools itself, and your underarms are one of the main places you sweat. Odor develops when sweat mixes with bacteria on the skin. A deodorant can help control odor, but its job title is not 'air conditioning'.4

What does an armpit sweat rash look like?

Heat rash usually causes small raised spots, an itchy or prickly feeling and mild swelling. Some spots contain fluid. The rash can look red on white skin and grey or white on brown or black skin, where it can be harder to see. The bumps sometimes hurt. Symptoms are often similar in adults and children, and heat rash cannot be passed to another person.15

Intertrigo is not automatically a fungal infection. Moisture makes skin surfaces stick together, increasing friction and skin damage. Bacteria or fungi can then overgrow; Candida, a type of yeast, is the most common cause of a secondary infection. Appearance alone is not always enough to identify the cause. A clinician can examine the fold and, if infection is suspected, take a skin scraping. Fungal infections, inflammation such as dermatitis, and folliculitis, inflammation around hair follicles, can resemble heat rash.236

What should you do first?

1. 1Move somewhere cooler, ideally an air conditioned room, and remove clothing covering the affected area.
2. 2Gently wash the underarms with cool or lukewarm water. Pat dry rather than scrubbing.
3. 3Leave the area uncovered when practical, or wear clean, loose clothing that does not rub.
4. 4Apply a cool damp cloth to ease the prickly feeling. Use it for up to 20 minutes; wrap an ice pack in a towel rather than placing it directly on skin.
5. 5Pause activities that make you sweat heavily until the heat rash clears. Tap or pat itchy skin instead of scratching it.

What should you leave off the rash?

For suspected heat rash, avoid thick ointments and products that block the skin. Sweat needs a route out, and heavy creams, ointments or powders can keep it trapped. Skip perfumed shower gels and creams, and avoid excessive soap or other irritants. Scratching can break the skin and allow infection to develop, so do not scrub or scratch in an attempt to remove the bumps.1356

Do you need a cream, powder or antiperspirant?

Cooling and drying are the main treatments for heat rash. If itching remains troublesome, a pharmacist can help choose calamine lotion, an antihistamine tablet or hydrocortisone, a steroid cream that reduces inflammation. Children under 10 need a doctor's advice before using hydrocortisone for heat rash. Calamine can dry the skin, so ask for advice if dryness develops. Antibiotics are used for a secondary bacterial infection, not as a routine heat rash treatment.56

Powders and antiperspirants sometimes help with prickly heat, but powders can also block pores and worsen an active rash. Ask a pharmacist before putting them on affected skin rather than treating every drying product as interchangeable. Stronger antiperspirants are also an option for excessive sweating; choosing one for sweat control is a separate decision from treating the rash.137

How long should heat rash take to clear?

Most heat rash settles within a day or two after moving to a cooler environment, although it can take a few days. This recovery time applies to heat rash, not every rash in an armpit fold. See a doctor if cooling and drying do not bring improvement after a few days, or if you suspect something other than heat is responsible.56

How can you stop it coming back?

Wear loose cotton clothing, change out of wet clothes and avoid unnecessary layers. Keep your bedroom cool and ventilated, use lightweight bedding and take cool baths or showers. During hot or humid weather, reduce heat exposure where possible and take breaks to cool down.356

Tight clothing can encourage heat rash, especially during exercise or in warm environments. Loose cotton clothing allows airflow, which is a better job description than 'second skin'. Anyone can develop heat rash; babies are particularly susceptible because their sweat ducts and temperature control are still developing. Avoid bundling a baby in too many layers.356

What if your armpits keep sweating heavily?

Sweating when you are hot or exercising is normal. Sweating when your body does not need to cool down can be hyperhidrosis, meaning excessive sweating. It can happen without an obvious reason, because of another condition or as a medicine side effect. A pharmacist can discuss stronger antiperspirants and gentler soap substitutes. See a doctor if self care is not helping, sweating interferes with daily activities, occurs at night, or you take medicine for another condition. A doctor can assess the cause and arrange treatment if needed.7

When should you get medical help?

• Seek prompt medical care for pus, a foul smell, tender raised bumps or other signs of infection.
• Get medical help for fever, chills, or skin around the rash that becomes warm or swollen.
• Have a painful rash or intense itching assessed rather than continuing home treatment alone.
• See a doctor if the rash does not improve after a few days. Contact your baby's doctor if you are worried about their rash.
• Be particularly alert to infection if you have diabetes or a weakened immune system, which increase the risk of intertrigo.