Fever in Babies

Medically Reviewed by Poonam Sachdev on June 26, 2024
Written by Stephanie Watson
5 min read

A fever in babies is one of the most common symptoms new parents face. Fortunately, it's not necessarily a sign of anything serious.

A baby's normal temperature averages 98.6 degrees F. A fever is a rectal temperature of 100.4 degrees F or higher or an armpit temperature of 99 degrees F or higher. Take a few readings when your infant is well to get a sense of what their normal temperature is. 

A fever isn't an illness. It's a symptom of one. A fever usually means that the body is fighting an illness and the immune system is working harder. If your baby has a fever, in most cases it means they've gotten a cold, flu, or other viral infection. Bacterial infections are another cause, and urinary tract infections are common causes of fevers in girls. Fevers in babies can also be a harmless reaction to a vaccine or a result of overheating on a hot day.

Some other causes that are more serious include: 

Newborn fever. A fever in the first 3 months of your baby's life is serious. It may be due to a bloodstream infection called sepsis. You should get medical treatment right away for fever in babies in this age group.

Meningitis. This is a bacterial infection in the tissue that covers your baby's brain and spine. It's a very serious condition. Symptoms include stiffness in your baby's neck, confusion, and headache. Your baby may be lethargic (unusually sleepy) or very fussy and unable to be soothed. If you notice these symptoms, get medical attention immediately. 

Is fever a sign of teething in babies?

When your baby is teething, the main signs are drooling and rubbing their gums. Fever is not a sign of teething. 

Your baby may be crankier and fussier than usual when they have a fever.

Other symptoms of a fever in babies include:

  • Poor sleeping
  • Poor eating
  • Frequent crying
  • Less activity and less interest in play
  • Skin that's warm to the touch and flushed
  • Trouble breathing
  • Stiff neck
  • Unusually sleepy and difficult to wake
  • More rapid heart rate and breathing
  • Blotchy skin
  • Convulsions or seizures
  • Sore throat
  • Headache
  • Sweating
  • Peeing less
  • Shivering
  • Unable to be calmed

Fever isn't always a reason to worry. If your baby is over 4 months and their fever isn't any higher than 104, this isn't considered an emergency. It's OK for a baby to have a mild fever for up to 5 days. If your baby is still playing, eating, drinking, and acting relatively normal, there's no cause for alarm. 

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. Don't use an old mercury thermometer because these pose a risk of poisoning if they break.

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

How to take a rectal temperature 

  1. Buy a digital rectal thermometer, available at any drugstore.
  2. Before and after use, wash the thermometer with soap and water or swab with disinfecting alcohol.
  3. Place a thick slab of petroleum jelly on the end with the metal bulb.
  4. Put your baby on their stomachor hold their legs up near their ears while they're on their back.
  5. 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).
  6. Insert the thermometer slowly into their anus about 1/2 inch -- just so that the metal bulb is inside.
  7. Gently hold the thermometer steady between your index and forefinger.
  8. Wait until it beeps and then pull the thermometer out.

If your baby is younger than 3 months and has a fever, contact their doctor right away. For older babies, try these tips:

  • Bathe them with lukewarm water. Always check the temperature of the water on your wrist before washing your baby.
  • Dress your infant in a light layer of clothes.
  • Give your baby enough fluids to avoid dehydration. Those fluids should be breast milk or formula. If they are older than 6 months, they can drink Pedialyte. Ask your baby's doctor for guidelines. 

Medicines to lower fever in babies

If your child is older than 2 months and your doctor says it is OK, you can give them children's acetaminophen. Children over 6 months can take children's ibuprofen. Never give babies aspirin because of the risk for a rare but dangerous condition called Reye syndrome. Ask your doctor about the dosage and read the package instructions before giving your child a fever-reducing medicine.

If your baby is younger than 2 months and has a rectal temperature over 100.4 degrees F, take them to the emergency room. If your child is older than 2 months, call your doctor if your baby:

  • Is lethargic or unresponsive
  • Has problems breathing or eating
  • Is crying uncontrollably 
  • Has a rash
  • Shows signs of dehydration, such as fewer wet diapers, a dry mouth, no tears when they cry, or a sunken soft spot on the head
  • Has a seizure
  • Is vomiting
  • Has diarrhea 
  • Has a stiff neck
  • Appears to have a severe headache or other pain
  • Has been in a very hot place, such as a hot car

Your baby can have a fever for many reasons. Most of the time, it's because they are fighting off a normal infection like cold or flu. If they are over 3 months old and still playing, eating, and drinking close to the way they normally would, you probably don't have to worry. If your baby is under 2 months old and has a fever, they need emergency medical attention. If they are over 2 months and are having more severe symptoms, call your doctor. 

When should you worry about a baby's fever?

If your baby is younger than 2 months, they need emergency medical care. If your child is older than 2 months and is lethargic, crying uncontrollably, has seizures, has diarrhea, is vomiting, has a rash, is dehydrated, has a stiff neck, is showing signs of severe pain, is having trouble breathing or eating, or has recently been in a hot place, such as a hot car, call their doctor. 

How do I bring my baby's fever down?

You can put them in a bath with lukewarm water and dress them in light clothing. You can also use children's acetaminophen or ibuprofen depending on their age and with your doctor's OK. 

What is a normal fever for a baby?

An average normal fever is 98.6 degrees F.

Is 99.5 a fever for a baby?

Yes, if it's an armpit temperature reading. If it's a rectal temperature reading, over 100.4 degrees F is considered a fever.