When your skin can't stand the summer

What are heat rash (Miliaria)?

Heat rash – also known as heat eruption, Miliaria or colloquially “sweat bumps” – are small, often itchy blisters or red spots. They typically occur at high temperatures. They develop when the sweat glands are blocked and sweat cannot escape freely from the skin. As a result, moisture builds up under the epidermis, leading to the characteristic skin irritations.

Areas of the body where heat and moisture accumulate are particularly affected, for example under the arms, in skin folds, on the back or under tight clothing. These situations create ideal conditions for heat rash. Heat rash can occur in adults and children, with infants being especially susceptible because of their delicate skin. Unlike a sun allergy, the sun is not the direct trigger; it merely contributes to overheating and increased sweating, creating the conditions for heat rash to develop.

Causes: how does heat rash develop?

Heat rash develops when the body's sweat can no longer escape freely through the skin. The cause is blocked ducts of the sweat glands, usually due to a mix of dead skin cells, dirt particles and bacteria. Instead of evaporating on the skin surface, sweat accumulates under the epidermis, causing small pustules or inflamed red areas.

They occur particularly often in strong heat, high humidity or during intense physical exertion, especially when the skin is further irritated by tight, warm or non‑breathable clothing. Infants and young children are especially at risk because their sweat glands are not yet fully developed and can become blocked more easily.

Recognising heat rash: what are common symptoms?

This rash typically appears as small, itchy changes to the skin, often accompanied by redness and a burning sensation. The body areas most affected are those that sweat a lot or are tightly covered by clothing, such as the neck, chest, back, armpits or groin. 

Depending on the depth of the blocked sweat gland, the appearance and discomfort differ. With a superficial blockage, pale, clear blisters form that are barely irritating and not inflamed. 

If the blockage is deeper in the epidermis, red, inflamed bumps or blisters develop that itch intensely and may ooze. In some cases small pus-filled pustules can form if bacteria enter the irritated skin. Although the symptoms are unpleasant, heat rash is usually harmless and clears up on its own with proper care and avoidance of overheating.

How long do heat rash lesions remain on the skin?

How long heat rash takes to disappear depends on its severity and on the external conditions. In many cases – especially with the mild form, Miliaria cristallina – the blisters subside after a few hours or within one to two days, provided the skin is sufficiently cooled and kept dry. 

With more pronounced forms such as Miliaria rubra, it can take several days for the epidermis to calm down fully. To speed healing it is crucial to avoid further irritation from heat, sweat and tight clothing. With appropriate care and some patience, the skin usually regenerates by itself.

What symptoms accompany heat rash in babies and children?

Heat rash is not only common but also particularly uncomfortable in infants and young children. The skin reactions usually present as small red blisters that can be filled with fluid. These areas often itch or burn intensely, which quickly causes discomfort on sensitive baby skin. If children scratch, the irritation worsens and the epidermis is further stressed.

Besides visible signs such as redness, slight swelling or broken blisters, many children also show changes in behaviour. They appear restless, cry more often or sleep worse – clear signs that they are uncomfortable in their skin.

On hot summer days or if the child is wearing clothing that is too warm, it is therefore important to watch their skin reactions closely so you can intervene in time and provide relief.

Are heat rash lesions painful or dangerous for my child?

Although heat rash may look worrying, it is generally harmless. It usually does not cause pain and does not pose a health risk to your child. What can be distressing is the accompanying itching or a mild burning sensation on the skin, especially in infants and young children who cannot express their discomfort.

If they scratch the affected areas, the epidermis can be further irritated and, in the worst case, small inflammations can develop. Therefore it is important to keep the skin cool, dry and as friction‑free as possible to provide quick relief and support healing.

Tips against heat rash: how to quickly soothe irritated summer skin

• Wear breathable clothing made from natural fibres. Fabrics like cotton or linen allow air to reach the skin and help absorb moisture. This reduces heat build‑up, which can clog the sweat glands – the main cause of heat rash.
• Avoid tight clothing and chafing seams. Friction on already irritated skin can worsen symptoms or promote new spots. Choose loose, airy cuts on hot days – your body will thank you.
• Stay in the shade as much as possible during heat. Direct sunlight raises body temperature and leads to increased sweating. A cool, airy place can help prevent heat rash from occurring in the first place.
• Shower with lukewarm water regularly. Lukewarm water gently removes sweat and dirt without irritating the skin. Very hot water can further stress the epidermis, while cold showers can cause strong temperature changes and strain the circulation.
• Change sweaty clothing as soon as possible. Moisture on the skin is an ideal breeding ground for irritation. A fresh T‑shirt or underwear can already make a big difference – especially during physical activity or on humid days.
• Use cooling home remedies. A cloth soaked in chamomile tea and cooled, or some healing clay, can soothe the affected areas and have an anti‑inflammatory effect. Make sure to only apply home remedies to intact skin.
• Use creams with zinc or calamine if needed. These ointments and creams relieve itching, reduce inflammation and support healing. Your pharmacy can give competent recommendations – also for sensitive skin.
• Resist the urge to scratch. As tempting as it may be, scratching can open the epidermis, lead to infections and delay healing. Cooling, gentle dabbing or specific anti‑itch products are better choices.
• Drink enough water. Good fluid intake supports your body's natural temperature regulation. This helps avoid excessive sweating and thus the formation of heat rash.
• Use apple cider vinegar as a mild home remedy. Diluted apple cider vinegar has antibacterial properties and can help calm inflammations. Apply it with a cotton pad – but only if the epidermis is not open or severely irritated.
• Avoid heavy, greasy creams in hot weather. Thickly applied skincare can seal the skin and further block the sweat glands. Lightweight, fragrance‑free moisturisers are better suited on hot days.
• If you tend to get heat rash, avoid spicy or strongly seasoned foods. These can unnecessarily increase sweating and worsen the skin condition. Alcohol and caffeinated drinks are also considered to promote sweating.
• Use cornstarch‑based body powder. A light powder can absorb excess moisture without blocking pores. Be sure to use powder sparingly and apply carefully.
• Keep a close eye on the nappy area for children. Heat and moisture accumulate particularly easily under a nappy. Change nappies regularly and let the skin air dry in between.
• Seek medical advice for persistent or infected heat rash. If symptoms do not improve after several days or get worse, see a dermatologist. In cases of pus‑filled pustules, fever or severe pain, medical treatment is required.

Heat rash is annoying but usually harmless – with proper care and a few simple measures it can be well prevented or quickly relieved. The key is to keep the epidermis dry, cool and free from friction to avoid irritation. Those who know their skin and respond to early signs can enjoy hot days without worry.