As temperatures rise, dermatologists are urging the public not to ignore red, blister-like rashes that can appear in hot weather. The condition, commonly known as heat rash or prickly heat, medically termed miliaria, affects an estimated 30 percent of people and can cause discomfort that feels like nettles stinging the skin.
Heat rash is caused by blocked sweat ducts, which trap sweat beneath the skin and lead to inflammation. According to consultant dermatologist Dr. Shin-Young Cho, the primary risk factors include heat, humidity, tight clothing, and prolonged pressure on the skin. There is also some evidence suggesting that certain skin bacteria can contribute to the plugging of sweat ducts, increasing the likelihood of developing the rash.
The most frequently affected areas are the torso, neck, and skin folds like the armpits and groin, where sweat glands are concentrated and moisture can easily become trapped. However, heat rash can occur anywhere sweat accumulates under clothing, though it is less common on the face.
Prevention is key to managing heat rash, experts advise. This involves keeping cool in well-ventilated areas, wearing loose, breathable clothing, taking cool showers, and avoiding strenuous exercise. Heavy skincare products, especially those containing occlusive ingredients like petroleum jelly, silicones, or shea butter, should also be avoided. Sunscreen, while necessary, can also build up on the skin with frequent reapplication; opt for unscented, oil-free formulas.
For treatment, consultant dermatologist Dr. Magnus Lynch suggests calamine lotion to soothe the hot, prickling sensation. Its zinc and ferric oxide content can help cool the skin and support the skin barrier as the body clears the blocked ducts. He notes that calamine lotion can be drying over time, so it might be beneficial to use it sparingly and switch to a light, fragrance-free moisturizer in the evening.
Antihistamine tablets can help alleviate itching, though they do not address the underlying cause of the rash, as it is not an allergic reaction. Non-drowsy options like cetirizine can be taken during the day, while sedating antihistamines like Piriton may help with sleep disruption at night. If engaging in physical activity, wearing moisture-wicking fabrics and showering soon after to remove sweat is recommended. Scratching should be avoided, as it can worsen irritation and increase the risk of infection.
While some dermatologists consider heat rash and sweat rash to be the same, others distinguish 'sweat rash' as candida intertrigo. This condition typically presents as a sore, raw inflammation, sometimes with cracked skin and scaling, often found in skin folds due to sweat and friction, and may involve an overgrowth of yeast and bacteria. For such cases, an anti-microbial hypochlorous spray might be helpful. Gentle hypochlorous mists can also help calm inflammation in heat rash without aggravating it.
Heat rash should not be confused with sun allergy, or polymorphic light eruption (PLE). Sun allergy results from an overreaction of skin to UV rays, typically appearing as red, itchy blotches and blisters on sun-exposed skin, rather than the small bumps characteristic of heat rash that often form in areas where sweat is trapped.
