Red bumps that appear on the neck after any kind of workout could be cholinergic urticaria or miliaria. Both conditions most often manifest in hot, humid conditions. Urticaria is the result of an allergic reaction, while miliaria occurs when sweat is trapped beneath the surface of the skin.
Cholinergic Urticaria
Cholinergic urticaria, a form of physical urticaria or hives, develops in response to heat, sweat or anxiety. Cholinergic urticaria most often manifests itself as itchy, red bumps along the trunk and arms, but it can also appear around the neck. Patients who suffer from cholinergic urticartia sometimes suffer from dermographism, or an exaggerated swelling when the skin is scratched, or other forms of urticaria.
Miliaria
Miliaria, also known as "heat rash" or "sweat rash," can appear in the form of miliaria crystallina, miliaria rubra or miliaria profunda. Miliaria shows up after exercise if the sweat ducts become obstructed. Bumps or blisters appear most often on the shoulders, neck, armpits and groin. Miliaria crystallina is the mildest form of heat rash and shows up as small, clear blisters located along the surface of the skin. Miliara rubra, located in the epidermis, or outside layer of skin, shows up as itchy, red bumps, or papules. A more severe form of heat rash, miliara profunda, manifests in the middle layer of skin or dermis, and produces painful red lumps.
Prevention and Treatment
Exercising in cool conditions and taking an oral antihistamine can stave off cholinergic urticaria. Miliaria occurs due to obstructed sweat ducts, so avoid fabrics or tight-clothing cause friction or prevent the skin from breathing. Pull your hair back to keep sweat from collecting around the neck, and exercise in an air-conditioned building. Apply calamine lotion to the affected areas to reduce itching.
Warning
Mild heat rash usually disappears on its own and doesn't require a doctor's care, but more serious forms of heat rash require the treatment of a dermatologist or primary care physician. Untreated miliaria can lead to bacterial infection.
Although rare, some people who suffer from bouts of urticaria can develop anaphylaxis, a form of life-threatening allergic reaction. Contact emergency services if you experience a difficulty breathing or swallowing, or feel dizzy or light-headed.
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