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.

Types of heat rash

The types of miliaria are classified according to how deep the blocked sweat ducts are. Signs and symptoms for each type vary.

  • The mildest form of heat rash (miliaria crystallina) affects the sweat ducts in the top layer of skin. This form is marked by clear, fluid-filled blisters and bumps (papules) that break easily.
  • A type that occurs deeper in the skin (miliaria rubra) is sometimes called prickly heat. Signs and symptoms include red bumps and itching or prickling in the affected area.
  • Occasionally, the fluid-containing sacs (vesicles) of miliaria rubra become inflamed and pus-filled (pustular). This form is called miliaria pustulosa.
  • A less common form of heat rash (miliaria profunda) affects the dermis, a deeper layer of skin. Retained sweat leaks out of the sweat gland into the skin, causing firm, flesh-colored lesions that resemble goose bumps.

When to see a doctor

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:

  • Increased pain, swelling, redness or warmth around the affected area
  • Pus draining from the lesions
  • Swollen lymph nodes in the armpit, neck or groin
  • A fever or chills
Jan. 20, 2015