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Parent’s Guide for Taking Newborn Temperatures

As a parent, there’s nothing more precious than your child. If you suspect your little one is running a fever, it can be worrisome — especially if they’re only a few months old.  

Because your baby has a developing immune system, some illnesses can become serious very quickly. This is why it’s important to know the signs of illness and get prompt medical care.

Read on to learn more about how to recognize a fever and take a newborn’s temperature and how to effectively treat the fever.

Normal body temperatures 

A newborn’s temperature will change as they adapt to life outside of the womb. 

“It’s normal for a baby’s temperature to fluctuate for various reasons, and it’s not always a bad thing,” said Vidya Surapaneni, MD, a pediatrician with Banner Children's. “A temporary rise in temperature could be a sign they are fighting an illness, but it can also change depending on their age, activity or the time of day.”

Though your newborn’s temperature will generally fall between 36.3 to 38 degrees Celsius or 97.4 to 100.4 Fahrenheit, there are instances where it could fall outside this range. When their temperature range goes over 38 degrees C or 100.4 F, this is considered a fever. 

Signs of a fever

Sometimes it can be difficult to know if your baby is running a fever, especially when they’re very young and can’t let you know they don’t feel well. If your baby’s behavior or activity level changes, and you think they have a fever, it’s good to take their temperature.

Some of the following signs, when paired with a fever, may indicate your baby is sick:

  • Appears flushed
  • Fussier
  • Nurses/eats less
  • Sleeps more
  • Sweats

What are the different types of baby thermometers?

Nowadays, parents have many options when it comes to taking a baby’s temperature. Long gone are those mercury thermometers, which can pose a threat to human health and the environment when broken or placed in the trash.

Today, many are digital multiuse thermometers, which can make it quicker and easier to determine if your little one has a fever. They don’t typically cost very much and can be used for various parts of the body.

The different methods to take a temperature include:

  • Rectal (anus)
  • Temporal artery (forehead)
  • Axillary (underarm)
  • Oral (mouth)
  • Tympanic (ear)

The values might differ slightly depending on which method you use, but they’re all important in their own ways. 

Other methods like plastic strip thermometers, pacifier thermometers and even smartphone temperature apps aren’t recommended. 

“These methods aren’t very accurate,” Dr. Surapaneni said. “Temp strips, in particular, use liquid crystal technology that has not shown to be reliable when compared to digital thermometers. Errors of lower temperatures in children often occur when they have a true fever.”

The most accurate way to take a newborn’s temperature is rectally

As squeamish as it may make you, especially if you’re new to the whole parenting a newborn thing, is to take your newborn’s temperature rectally. These thermometers are perfectly safe and won’t hurt your baby in any way.

“Rectal thermometers are the preferred and most accurate method of checking temperatures for newborns and infants less than 3 months of age, because research shows they are the most accurate measure of core body temperature,” Dr. Surapaneni said. “While tympanic and temporal thermometers provide speedy results and can be accurate in older babies, they aren’t recommended for newborns.”

In fact, the American Academy of Pediatrics recommends rectal thermometers as the “gold standard” for children under three years old. 

How to take a rectal temperature?

A rectal thermometer has a similar shape as an oral thermometer but usually has a shorter and stubbier tip, making it easier to slip into the rectum. 

Make sure when purchasing you don’t confuse these with oral thermometers. It should be designated and clearly labeled as a rectal thermometer as oral thermometers can cause injury. You also don’t want an oral thermometer to end up in someone’s mouth later – blech! 

  • Clean the end of the thermometer with rubbing alcohol or warm soap and water and dry before and after each use. 
  • Lay your newborn on their back on a flat surface, such as a changing table. 
  • Lubricate the silver bulb of the thermometer with a lubricating jelly, such as Aquaphor or Vaseline. However, check with the manufacturers label whether water-soluble or petroleum jelly should be used.
  • Using one hand, separate your baby’s buttocks (cheeks) with your thumb and forefinger, and with your other hand gently insert the bulb one-half inch to one inch inside. Stop if you feel any resistance.
  • Soothe your baby and speak to them as you wait for the temperature to show. 
  • When it beeps or signals, read and record the number on the screen.

What to do if your newborn is running a fever?

If the rectal thermometer or temporal reading is above 100.4 degrees F:

  • Contact your pediatrician.

Visit the urgent care or emergency room if your baby’s fever also includes these symptoms:

  • Rash
  • Vomiting
  • Diarrhea
  • Coughing or congestion (especially if its flu/RSV season)
  • Inconsolable or won’t stop crying
  • Difficulty breathing
  • Difficulty waking up to feed/lethargic

Save your spot for an urgent care visit.
Find the Banner Health emergency department closest to you.

Call 911 if your baby is turning blue, isn’t breathing, has abnormal movements or twitching or is not waking up to feed.


A fever can be scary, especially if you have a newborn baby. 

There are many reasons for your baby’s temperature to fluctuate, some not always a cause for concern. However, you know your baby better than anyone.

If they’re showing signs of a fever, a rectal thermometer is the best method. Contact your pediatrician if your newborn’s fever is higher than 100.4 degrees F. They will be able to help diagnose the underlying cause and recommend treatment.

Before long, your little one will be feeling better.

For other parenting tips, check out:

Children's Health Parenting