Always use a digital thermometer to check your child’s temperature. Never use a mercury thermometer.
For infants and toddlers, be sure to use a rectal thermometer correctly. A rectal thermometer may accidentally poke a hole in (perforate) the rectum. It may also pass on germs from the stool. Always follow the product maker’s directions for proper use. If you don’t feel comfortable taking a rectal temperature, use another method. When you talk to your child’s healthcare provider, tell him or her which method you used to take your child’s temperature.
Here are guidelines for fever temperature. Ear temperatures aren’t accurate before 6 months of age. Don’t take an oral temperature until your child is at least 4 years old.
Infant under 3 months old:
Ask your child’s healthcare provider how you should take the temperature.
Rectal or forehead (temporal artery) temperature of 100.4°F (38°C) or higher, or as directed by the provider
Armpit temperature of 99°F (37.2°C) or higher, or as directed by the provider
Child age 3 to 36 months:
Rectal, forehead, or ear temperature of 102°F (38.9°C) or higher, or as directed by the provider
Armpit (axillary) temperature of 101°F (38.3°C) or higher, or as directed by the provider
Child of any age:
Repeated temperature of 104°F (40°C) or higher, or as directed by the provider
Fever that lasts more than 24 hours in a child under 2 years old. Or a fever that lasts for 3 days in a child 2 years or older.