Can sweat cause a rash?

Why does sweating cause a rash?

Sweat is a clear, salty liquid that helps cool your body. Sweating more in hot weather or during exercise is normal. Heat rash develops when sweat cannot escape through its usual channels and builds up under the skin instead.12

Hot, humid weather, intense activity, fever and clothing or dressings that trap moisture can contribute. Heat rash affects all ages. Babies are particularly susceptible because their sweat ducts are immature and they cannot control their temperature as well as older children and adults.34

What does heat rash look like?

Typical signs are small raised spots, itching or a prickly feeling, and mild swelling. Some spots contain fluid. The rash looks red on white skin but can look grey or white, or be harder to see, on brown or black skin. Heat rash can spread across the body, but it is not contagious.4

In adults, heat rash often affects the upper body, scalp, neck and skin folds, especially where clothing rubs. In children, it commonly affects the body and folds around the neck, armpits or groin. Another form produces tiny clear blisters that look like beads of sweat and break easily.3

What should you do now?

1. 1Get out of the heat and remove wet or tight clothing.
2. 2Cool your skin with a cool shower or bath.
3. 3Apply a cool damp cloth, or an ice pack wrapped in a tea towel, for up to 20 minutes to calm itching.
4. 4Tap or pat the rash instead of scratching. Avoid perfumed shower gels and creams.

Choose loose cotton clothing, rather than asking your wardrobe to perform packaging duties. Lightweight bedding and a cool, ventilated bedroom also help reduce heat exposure.34

Use fans or air conditioning to keep cool, giving the thermostat a skincare job for once. For outdoor exercise, choose the coolest parts of the day or move your workout into an air conditioned space. Change out of tight workout clothes and shower immediately afterwards.1

Do you need a cream?

Cooling is the main treatment. A pharmacist can help you choose calamine lotion, an antihistamine or hydrocortisone cream if needed. Children under 10 need advice from a doctor before using hydrocortisone for heat rash. Avoid routinely covering heat rash with moisturizer; if calamine leaves the area dry, ask whether an emollient, a moisturizing treatment, is appropriate.345

Most heat rash clears within a day or two after moving to a cooler environment, although it can take a few days. Arrange a medical appointment if it does not improve after a few days, worsens, or your baby has a rash that worries you.134

Could the bumps be something else?

Sweat mixed with oil and bacteria can clog pores and contribute to acne. Folliculitis, an infection of the openings where hairs grow, causes spots that resemble pimples but tend to be itchy and tender. To reduce sweat related breakouts, blot sweat with a clean towel instead of rubbing, and wash sweaty clothes, hats and headbands before reusing them.1

When should you get medical help?

Contact a clinician if the area feels warm or drains pus, which can signal infection. Dizziness, nausea, vomiting or headache after heat exposure can indicate heat exhaustion and need immediate medical attention. Confusion, behaviour changes or slurred speech can indicate heat stroke, a medical emergency.5

Sweating heavily even while resting or in cool temperatures can be hyperhidrosis, meaning excessive sweating. Contact a clinician if sweating is prolonged and unexplained or happens mostly during sleep. Antiperspirants can irritate skin, so a rash where you apply one is not automatically heat rash.6