Heat rash — also known as prickly heat and miliaria — isn't just for babies. It affects adults, too, especially during hot, humid weather.
Heat rash develops when blocked pores (sweat ducts) trap perspiration under your skin. Symptoms range from superficial blisters to deep, red lumps. Some forms of heat rash feel prickly or intensely itchy.
Heat rash usually clears on its own. Severe forms of the condition may need medical care, but the best way to relieve symptoms is to cool your skin and prevent sweating.
Miliaria rubra (A), one type of heat rash, appears as red clusters of small blister-like bumps that can produce intense itching. Miliaria crystallina (B), another type of heat rash, appears as clear, fluid-filled bumps that produce no other signs or symptoms.
Adults usually develop heat rash in skin folds and where clothing causes friction. In infants, the rash is mainly found on the neck, shoulders and chest. It can also show up in the armpits, elbow creases and groin.
The types of miliaria are classified according to how deep the blocked sweat ducts are. Signs and symptoms for each type vary.
Heat rash usually heals by cooling the skin and avoiding exposure to the heat that caused it. See your doctor if you or your child has symptoms that last longer than a few days, the rash seems to be getting worse, or you notice signs of infection, such as:
Heat rash develops when some of your sweat ducts clog. Instead of evaporating, perspiration gets trapped beneath the skin, causing inflammation and rash.
It's not always clear why the sweat ducts become blocked, but certain factors seem to play a role, including:
Factors that make you more prone to heat rash include:
Heat rash usually heals without problems, but it can lead to infection with bacteria, causing inflamed and itchy pustules.
To help protect yourself or your child from heat rash:
You don't need tests to diagnose heat rash. Your doctor diagnoses it by its appearance.
Avoiding overheating may be all you need to do for mild heat rash. Once skin is cool, heat rash tends to clear quickly.
More-severe forms of heat rash may require ointments you apply to your skin to relieve discomfort and prevent complications. Such topical treatments may include:
Tips to help your heat rash heal and to be more comfortable include the following:
A doctor's appointment usually isn't necessary for heat rash. If your rash is more severe, you may want to see your primary care doctor or a doctor who specializes in skin disorders (dermatologist) to be sure it's heat rash and not another skin disorder.
Before you go, it's a good idea to list questions you have about your condition. For heat rash, questions to ask your doctor include: