Taking Your Baby's Temperature

Reviewed by Amita Shroff, MD on June 21, 2022

There are many technical skills to learn with your new baby. One of them is being able to take an accurate temperature. A fever is one of the key indicators of a potentially serious infection in the first months of your baby's life.

Taking Baby's Temperature Rectally

The goal of taking a temperature is to assess how warm it is inside of the body. This means that the most accurate measurement will be one taken inside the body, which means rectally. This is a critical point. Since any infection in the newborn period is so serious, a rectal temperature must be taken in newborns to provide the most accurate measurement (after the first few months, the risk of a serious infection lessens, and temperatures may be taken on the skin, mouth or ear.

How to Take a Rectal Temperature in Your Baby

  1. Buy a digital rectal thermometer to use.
  2. Place a thick slab of petroleum jelly on the base of the thermometer, the end with the metal bulb.
  3. Put your baby on their stomach or hold their legs up near their ears while they're on their back.
  4. Stabilize them so they don't wiggle too much -- with a hand on their back (if they are on their stomach) or holding their feet firmly (if they're on their back).
  5. Insert the thermometer slowly into their anus about 1/2 inch -- just so that the metal bulb is inside.
  6. Gently hold the thermometer steady between your index and forefinger.
  7. Wait until it beeps and then pull the thermometer out.

Any temperature of 100.4 Fahrenheit and higher in a young baby -- 12 weeks or younger -- is considered a fever and a reason to call your doctor immediately. You can always call your doctor for a sick baby, even if the baby doesn't have a fever.


Show Sources


"Fever" Powell K. in Nelson Textbook of Pediatrics, 17th edition. Behrman R, Kliegman R and Jenson H (eds.), Saunders: 2004.

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