If you break out in a rash during or after exercise, you may be suffering from heat rash -- also known as prickly heat or milaria – or cholinergic urticaria, which is a type of hives caused by heat. There are differences in what causes each of these conditions, but neither is usually serious.
The heat rash known as milaria occurs when your sweat ducts become blocked and perspiration is, therefore, trapped under your skin. It is most common in babies -- whose sweat ducts haven't formed properly -- and in people who live in very hot and humid climates.
Cholinergic urticaria occurs when your skin is hypersensitive to increases in body temperature. As well as exercise, cholinergic urticaria can be brought on by eating spicy food, a hot shower, and stress or anxiety.
Heat Rash and Exercise
It is not unusual to develop either form of heat rash after exercise. Sweating heavily due to a particularly intense workout can cause the sweat ducts to become blocked and give rise to milaria. A heavy exercise session will also increase your body temperature and may bring on a bout of cholinergic urticaria if your skin is susceptible to heat.
Both conditions appear as red bumps on the skin, which can be itchy or feel prickly. You can experience either form all over your body during or after exercise, or it may appear in specific areas -- usually your chest, arms, legs and face. Heat rash is common in skin folds, such as your elbows, and wherever clothing is likely to create friction against your skin such as your groin and armpits.
The best treatment for both forms of heat rash is keeping your skin cool, as well as wearing lightweight, breathable fabrics such as cotton. Over-the-counter treatments such as calamine lotion can help soothe itching.
Neither form of heat rash is usually serious and symptoms will generally go away without any specific treatment. But, while the symptoms of cholinergic urticaria don't tend to last long after exposure to heat, your skin can remain sensitive to temperature increases for many years. See a doctor if your heat rash doesn't go away after a few days and/or gets worse; the red bumps are painful or become infected; the lymph nodes in your neck, armpit or groin are swollen; or you feel feverish.