When Your Child Has Heat Rash (Prickly Heat)

Use a digital thermometer to check your child’s temperature. Don’t use a mercury thermometer. There are different kinds and uses of digital thermometers. They include:

  • Rectal. For children younger than 3 years, a rectal temperature is the most accurate.
  • Forehead (temporal). This works for children age 3 months and older. If a child under 3 months old has signs of illness, this can be used for a first pass. The provider may want to confirm with a rectal temperature.
  • Ear (tympanic). Ear temperatures are accurate after 6 months of age, but not before.
  • Armpit (axillary). This is the least reliable but may be used for a first pass to check a child of any age with signs of illness. The provider may want to confirm with a rectal temperature.
  • Mouth (oral). Don’t use a thermometer in your child’s mouth until they are at least 4 years old.

Use a rectal thermometer with care. Follow the product maker’s directions for correct use. Insert it gently. Label it and make sure it’s not used in the mouth. It may pass on germs from the stool. If you don’t feel OK using a rectal thermometer, ask the healthcare provider what type to use instead. When you talk with any healthcare provider about your child’s fever, tell them which type you used.

Below is when to call the healthcare provider if your child has a fever. Your child’s healthcare provider may give you different numbers. Follow their instructions.

When to call a healthcare provider about your child’s fever

For a baby under 3 months old:

  • First, ask your child’s healthcare provider how you should take the temperature.
  • Rectal or forehead: 100.4°F (38°C) or higher
  • Armpit: 99°F (37.2°C) or higher
  • A fever of ___________as advised by the provider

For a child age 3 months to 36 months (3 years):

  • Rectal or forehead: 102°F (38.9°C) or higher
  • Ear (only for use over age 6 months): 102°F (38.9°C) or higher
  • A fever of ___________ as advised by the provider

In these cases:

  • Armpit temperature of 103°F (39.4°C) or higher in a child of any age
  • Temperature of 104°F (40°C) or higher in a child of any age
  • A fever of ___________ as advised by the provider