Miliaria is a skin rash that happens when sweat glands get blocked, letting sweat build up under the skin. It's also called heat rash, prickly heat, or sweat rash. It can be a little itchy, but miliaria (mill-ee-AR-ee-uh) doesn't cause other symptoms and isn't serious. You can help the rash go away within a few days by keeping your child's skin cool so they sweat less.

Keep your child cool:

• Try to keep them in a cool environment, with air conditioning or a fan, if possible.
• You can put a thin, clean cloth dipped in cool water on the rash a few times a day. Take the cloth off when it is no longer cool.
• Dress them in lightweight, loose cotton clothing or, if possible, let their skin air out without clothing.
• Give them plenty of cool liquids to drink.

To avoid making your child's rash worse:

• Bathe them in plain, lukewarm water no more than once a day. Don't use soap until the rash is gone.
• Avoid using powders, creams, or ointments. 
• Keep their fingernails trimmed so they don't scratch the skin.
• Don't put adhesive bandages over the rash.
• If the rash is in the diaper area: Until it heals, consider using cloth diapers or try to leave the diaper open or off as much as possible.

• The rash does not go away after a few days.
• The rash gets worse.
• The skin looks infected (is red, warm, swollen, or oozing pus).
• Your child:
  • has new symptoms, such as a runny nose or a cough
  • is over 3 months old and has a fever
  • is very uncomfortable from itching

Your child:

• is under 3 months old and has a rectal temperature of 100.4°F (38°C) or higher
• seems very sick or is hard to wake up

What causes miliaria? Heat rash happens when sweat collects behind blocked sweat ducts. Often, it happens when a child is sweating a lot or in warm, humid climates. A heat rash can happen at any age but is most common in babies. 

What are the symptoms of heat rash? The rash from miliaria has little red bumps or clear blisters. It often happens on the upper chest or back, the head, the arms, the neck, in body folds, or anywhere the skin doesn't get enough air or rubs together or against tight clothing. Miliaria is not contagious.