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What are the Causes of Fever in Infants?

What to do when your baby has a fever, when to call your doctor

A child with a fever gets his temperature taken.

What to do when your baby has a fever, 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 infants and children will do that.


“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.”

Is fever a symptom of an illness?

A fever is a higher-than-normal body temperature. It is not an illness. Instead, it is a sign or symptom of one. “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.

What is fever in infants?

Compared to adults, young children are more likely to develop a fever in reaction to an infection.


Infants younger than 3 months old who have a fever need immediate medical attention even if they appear well and show no other signs of being ill.


Fever in babies is defined as a rectal temperature above 100.4 degrees Fahrenheit or 100.4 F (38 degrees Celsius or 38 C), or an oral temperature above 99 degrees F (37.2 C). Rectal thermometers are recommended for children up to age 3.

What causes fever?

Fever alone is rarely harmful. Only about 1 out of 100 children with fever have a serious medical problem that needs to be treated by a doctor, according to the National Institutes of Health.


Fever most commonly accompanies illnesses, such as:


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


About 10 percent of young infants with fever are found to have urinary tract infections.


In rare cases, young infants with fever can have more serious underlying infections that can rapidly progress. Among the most serious are infections of the blood (sepsis), and meningitis, which is inflammation of the brain and spinal cord.

Home remedies for infants with fever

Medication is generally not needed to treat fever in children unless the child is experiencing discomfort or has another condition.


You can find two main types of pain relievers in the children’s section of your local drug store. One is acetaminophen (Tylenol). The other are nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil) or naproxen (Aleve).


The American Academy of Pediatrics (AAP) recommends consulting with your pediatrician before giving Tylenol to babies under 3 months old. The AAP recommends waiting until an infant is 6 months old or older before giving them NSAIDs).


Make sure to read the label and follow instructions before giving medicine. For example, follow the age, weight and dosing recommendations listed on the label.


If you’re not sure which medicine to give your child, or how much consult with your pediatrician.

When to call your doctor

Call your doctor if your child, in addition to fever, exhibits the following symptoms:


  • Drowsiness, fussiness
  • Stiff neck, severe headache, severe sore throat, severe ear pain, unexplained rash, repeated vomiting or diarrhea
  • Has signs of dehydration but is unable to take in fluids
  • Has had a febrile seizure

What is a febrile seizure?

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


During a convulsion, the child may have a high fever, lose consciousness and shake or jerk their arms and legs. Unless a convulsion is prolonged (lasting more than 15 minutes) or there is something else going on, a febrile seizure does not mean the child has epilepsy.


Though they are rare and usually harmless, parents are urged to call their doctor as soon as possible after the first febrile seizure. “While this is a scary event, most febrile seizures are brief and do not cause long-term health problems,” says Dr. Wilson.

What if child has fever but no other symptom?

When it comes to evaluating babies who have fever but otherwise seem well, the challenge is to find the cause quickly while avoiding putting the baby through unnecessary tests or hospitalizations.


Fortunately, there is more guidance today. AAP recently issued a new set of guidelines to help doctors evaluate and treat well-appearing infants 8-to-60 days old who have fever.


The AAP guidelines break down recommendations for three infant age ranges: 8 to 21 days; 22 to 28 days and 29 to 60 days. Newborns in their first week of life have different needs and were not included in the report.