Fever in Babies

A fever in babies can be one of the scariest symptoms for parents, especially when that fever is high or the baby is only a few weeks old.

Here's what causes infant fevers and what to do when your baby gets a fever.

What Causes Infant Fevers?

A fever isn't an illness -- it's considered a symptom of one. A fever usually means that the body is fighting an illness and the immune system is working. If your baby has a fever, in most instances it means he has probably picked up a cold or other viral infection. Although they are less common in infants, pneumonia, urinary tract infections, ear infections, or a more serious infection such as a blood bacterial infection or meningitis may be causing a fever.

Other causes of fever in babies include:

  • Reaction to a vaccination
  • Becoming overheated from being dressed too warmly or spending too much time outside on a hot day

Fever in Babies: What Are the Signs?

Your baby may act differently, and he may also be crankier and fussier than usual.

Other symptoms of a fever in babies include:

  • Poor sleeping
  • Poor eating
  • Lack of interest in play
  • Less active or even lethargic
  • Convulsions or seizures

How Do I Take My Baby's Temperature?

You can take a child's temperature a few different ways, such as via the rectum (rectally), mouth (orally), ear, under the arm (axillary), or at the temples. The American Academy of Pediatrics (AAP) recommends only using digital thermometers in children. Mercury thermometers should not be used because they pose a risk of mercury exposure and poisoning if they break.

Rectal thermometers provide the most accurate temperature readings and can be easiest to take in an infant. 

To take a rectal temperature, first make sure the thermometer is clean. Wash it with soap and water or wipe it with rubbing alcohol. Lay your baby on his belly or on his back with legs bent toward the chest. Apply a little bit of petroleum jelly around the thermometer bulb and gently insert it into the rectal opening. Hold the digital thermometer in place for about 2 minutes until you hear the beep. Then gently remove the thermometer and read the temperature.

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At What Temperature Does My Baby Have a Fever?

A baby's normal temperature can range from about 97 to 100.3 degrees Fahrenheit. Most doctors consider a rectal temperature of 100.4 F or higher as a fever.

 

When to Call Your Doctor

According to the AAP, call your doctor if your baby:

  • Is under age 3 months and has a fever; if your baby is under 2 months and has a fever, it is considered an emergency. Seek immediate medical care.
  • Is lethargic or not responsive
  • Has problems breathing or eating
  • Is very cranky, fussy, or difficult to calm down
  • Has a rash
  • Shows signs of dehydration, such as fewer wet diapers, dry mouth, no tears with crying, or sunken soft spot on the head
  • Has a seizure

It can be hard for doctors to tell whether a newborn has a simple virus (like a cold) or a more serious infection (like a UTI, pneumonia, or meningitis). That's why doctors will sometimes order special tests (such as blood or urine tests, a chest X-ray, or a spinal tap) to pinpoint the cause of an infant's fever.

What Should I Do If My Baby Has a Fever?

If your baby is under age 1 month and has a fever, contact your child's doctor right away. For older babies, try these tips:

  • Bathe your child with lukewarm water. Always check the temperature of the water on your wrist before washing your baby.
  • Dress your baby in a light layer of clothes.
  • Give your baby enough fluids to avoid dehydration. Those fluids should be breast milk, formula, an electrolyte solution, or water, depending on the baby’s age. Ask your baby's doctor for guidelines. A dehydrated baby may have fewer wet diapers, no tears with crying, or a dry mouth.
  • If your child is older than 6 months and your doctor says it is OK, you can give your baby either children's acetaminophen or children's ibuprofen. Never give babies aspirin because of the risk for a rare but dangerous condition called Reye's syndrome. Also, do not give a baby under age 6 months any medicines that contain ibuprofen. Be sure to ask your doctor about the dosage and read the package instructions before giving your baby a fever-reducing medicine.

If you are concerned about your baby's fever, call your doctor for advice and reassurance.

WebMD Medical Reference Reviewed by Hansa D. Bhargava, MD on November 13, 2019

Sources

SOURCES:

Merck Manual: "Fever."

American Academy of Pediatrics: "How to Take a Child's Temperature."

The Journal of the American Medical Association, March 10, 2004.

Kidshealth.org: "Fever and Taking Your Child's Temperature."

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