Most babies will have at least one fever during infancy. A fever is in a way a good sign—it means that baby’s immune system is fighting viruses or bacteria to protect itself. 

The best way to measure fever in a baby or toddler is by taking a rectal temperature. Most physicians recommend using a rectal digital thermometer rather than a mercury thermometer, which can break and expose baby to mercury, which is a toxin. 

To take a rectal temperature:

• Clean the end of the thermometer with rubbing alcohol or soap and water.
• Put a disposable plastic sleeve on the thermometer.
• Put a small amount of petroleum jelly on the end of the thermometer.
• Lay your baby on his belly and hold him firmly by placing your hand across the small of the back.
• With your other hand, turn on the thermometer and then insert it 1.3 cm to 2.5 cm into the anal opening. (Do not insert it any farther.)  Hold it in place using two fingers, while keeping your hand cupped around baby’s buttocks.
• Hold the thermometer in place for about 1 minute until you hear it beep.
• Remove the thermometer, throw the plastic sleeve away, and check the reading. A rectal reading over 38˚C may indicate a fever.

When to call the doctor:

• If your child is age 2 months or younger and the temperature is above 38˚C, call your doctor immediately
• If your child is age 3-6 months, and the temperature is above 38.3˚C, or if your child is older than 6 months and the temperature is above 39.4˚C,  you may need to call your doctor, especially if your child has other symptoms such as:
• A sore throat
• An earache
• A cough
• An unexplained rash
• Repeated vomiting or diarrhea
• Extreme fussiness
• Excessive sleepiness
• If your child is over age 1 year and a high fever lasts for more than 24 hours
• If your child becomes delirious (talks strangely, “sees” things that aren’t there, acts frightened)
• If you child has a febrile convulsion—in which he stiffens, twitches, rolls his eyes, then is unresponsive for a short time. Although febrile convulsions are almost always harmless, they should be reported promptly to your doctor