Heat rash (miliaria)

What is heat rash?

Heat rash, or miliaria, is a raised rash that consists of small bumps. Also called "prickly heat," the little bumps contain sweat (perspiration) that could not get to the skin's surface and evaporate. It is common in babies and young children. The rash usually disappears on its own.

Signs and symptoms of heat rash

The rash looks like droplets of sweat that are trapped under the skin. The fluid may be clear or milky white. The bumps are only a few millimeters wide. The rash may also appear red on your child's skin.

The rash usually appears where babies and children sweat the most, such as:

• forehead
• neck
• armpits
• buttocks
• groin
• shoulders
• chest
• elbow creases
• behind the knees

Your baby may appear irritated, or your child may complain of the rash being itchy or having a prickly feeling. Often, the rash will go away on its own in a few days in a cooler environment.

Causes of heat rash

Clogged (blocked) sweat ducts are the main cause of heat rash. When ducts are blocked, sweat cannot escape. Instead of evaporating on the skin's surface, sweat droplets are trapped under the skin, causing inflammation and rash.

Clogged sweat ducts are caused by many factors. Most often, babies develop the rash due to one of the following reasons:

• wearing too much clothing or clothing that does not allow sweat to evaporate
• fever
• environmental factors such as hot, humid weather or a room that is too hot

Babies with fever or newborns in incubators may develop blocked sweat ducts. Some individuals are at risk for recurrent episodes of heat rash.

How you can help your child with heat rash

Children, especially babies, who develop heat rash should be cooled to prevent overheating and sweating. Treating the rash itself is very simple:

• Remove clothing as often as possible.
• Do not overdress your child.
• Give your child a lukewarm bath with non-drying soap.
• After bathing, let your baby or child air-dry instead of towelling off.
• Keep your child's room well ventilated and at a comfortable temperature.
• Dress your child in loose-fitting, light cotton clothing or breathable clothing. Avoid dressing your child in tight-fitting clothing.
  

Complications

Rarely, heat rash can become infected with bacteria. This makes the fluid-filled bumps painful, bigger and more inflamed.

A very rare complication of heat rash is heat exhaustion. If your child's sweat ducts are clogged, the body cannot cool itself properly. Untreated heat exhaustion can lead to heat stroke. This is a dangerous illness that can lead to organ damage or death. Heat stroke happens when a child's body creates more heat than it can release. The child's core body temperature increases rapidly, to 40°C or higher.

When to seek medical assistance

In general, heat rash heals without medical treatment. In rare instances, the rash can become infected.

If your child's rash lasts longer than a few days or the rash seems to be getting worse, make an appointment with your child's health-care provider.

Seek care right away if your baby or child has any of the following signs:

• increased pain or swelling around the rash
• pus draining from the fluid-filled bumps
• swollen lymph nodes (small bumps) in the armpit, neck or groin
• fever or chills