What are Common Causes of Fever in Infants?

Learn what it could be and when to call your doctor

A baby with fever gets temperature taken with thermometer.

Learn what it could be and when to call your doctor

It’s normal to worry when your child is running a fever. The younger your child is the more worried you are likely to be. Fever in children, especially infants, will do that.

Remember, most fevers aren’t harmful, but they still require special attention. Knowing what causes fevers, how to treat them and when to contact your doctor can help ease your worry.

“Learning what causes fevers and how to reduce fever in children with or without medication will help ease your anxiety,” says Karen Wilson, MD, a pediatrician at Scripps Clinic Carmel Valley. “Knowing when to call your doctor is a critical part of that learning.”

To diagnose and treat a fever, doctors will ask about a child’s symptoms and history, check their temperature and look for warning signs during a physical exam.

What does fever mean?

Fever is not an illness itself but rather a symptom of an underlying issue. “It is the body’s way of fighting an infection and can actually stimulate the body’s immune system to help to fight off the infection,” says Dr. Wilson.

Only a small percentage, just 1 in 100 kids with fever, require medical attention for a serious issue.

Children are more likely than adults to get a fever when they have a viral or bacterial infection. Common infections include:

  • Common colds
  • Flu
  • RSV
  • Croup
  • Ear infections
  • Pneumonia
  • Urinary tract infections
  • Throat or sinus infections
  • Intestinal bowel infections


Bacteria or a virus can cause ear infections after a cold. Your pediatrician can diagnose and determine the appropriate treatment for an ear infection. If it is a bacterial infection, your child may require antibiotics. Around 10% of young infants with a fever have infections in their urinary tract.

Sometimes, babies with a fever may get very sick and need immediate medical help for serious infections. These infections can include sepsis in the blood and meningitis in the brain or spinal cord.

Babies can have fever for other reasons too, including:

  • Reaction to a vaccine, which is usually mild
  • Overheating, from hot weather or wearing too much clothing

Teething can raise body temperature but does not cause a true fever.


There are different types of thermometers: digital, temporal (forehead) and tympanic (ear).

The American Academy of Pediatrics recommends using digital thermometers to take a child’s temperature. The tip sensor measures body temperature when it touches the skin.

Digital thermometers measure temperature in a child’s bottom (rectal), mouth (oral) or armpit.

Know for example:

  • Rectal thermometers are the most accurate.
  • Oral and ear temperatures are accurate if done correctly.
  • Armpit temperatures are the least accurate but can still be used to check a child's temperature.

 Consider the child’s age when choosing a thermometer.

  • Rectal temperature gives the best reading, especially for infants under 3 months of age.
  • Use oral thermometers only for children age 4 and older.
  • Ear thermometers are safe for children 6 months and older to use.
  • Forehead thermometers work for kids of all ages.

What is a high temperature?

A normal temperature for a child can change based on their age, how active they are, and the time of day. The usual body temperature is about 98.6 degrees Fahrenheit. A fever is typically 100.4 degrees or higher.

Caring for a fever with fever

Children with a fever don’t always need medicine unless they are uncomfortable or have other health issues. Doctors recommend parents focus on keeping their kids comfortable rather than just trying to lower their temperature.

There are many ways to do this, including:

  • Dressing your baby in light clothing
  • Giving plenty of fluids to prevent dehydration
  • Monitoring activity and comfort level

Things you should not do include:

  • Don’t use rubbing alcohol or ice water to cool your child.
  • Don’t stress if your child isn't eating solid food yet; fluids are important when you have a fever.
  • Don’t wake your child for fever medicine.
  • Never give aspirin to your child.
  • Don’t give your baby any medication without first consulting your doctor.

The main pain relievers for kids are:

  • Acetaminophen (Tylenol) if your child is over 3 months old
  • Ibuprofen (Advil, Motrin) if your child is over 6 months old

Follow the age, weight and dosing recommendations listed on the medicine label.

When to call your doctor

Call your doctor right away if your child is 2 months old or younger with a rectal temperature of 100.4 degrees or higher. It’s important to see a doctor fast, even if the baby seems fine. The doctor can figure out why the baby has a fever early on. This might prevent more tests or trips to the hospital.

If a fever goes above 104 degrees multiple times, seek medical help no matter how old the child is.

Seek help if your child has a fever and other symptoms, including:

  • Trouble breathing
  • Rash
  • Drowsiness,
  • Stiff neck
  • Vomiting, or dehydration
  • Febrile seizures

Febrile seizures are fever-induced convulsions that can occur in children between 6 months old and 5 years of age.

These seizures are typically rare and not dangerous. It’s important to inform your doctor if they happen. “While this is a scary event, most febrile seizures are brief and do not cause long-term health problems,” says Dr. Wilson.

Caring without fear

Parents worry when their child has a fever, especially if they have young kids. This can make them anxious. Knowing the reason for the fever and when to visit a doctor can reduce stress and fear.

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