Should I Worry About My Baby’s Fever?

A baby's fever can be upsetting to new and experienced parents alike, and it's especially alarming if your child has other symptoms. But there are many reasons why you may see a fever in babies—even teething can cause tiny rises in temperature—and most of these causes aren't life-threatening.

Fever is normally a welcome sign that the body is fighting an infection to stay healthy, but there are times when a fever and related symptoms may signal a true emergency. In those cases, calling your child's pediatrician or 911 for help is the right move.

This article will help you understand some of the reasons for a baby's fever, and when it's important to call a professional. We'll be focusing on fevers in babies and infants under the age of 12 months.

Causes of Fevers
Verywell / Jiaqi Zhou

What Causes Fever

Before you get too concerned about your baby's temperature, it's important to know why fevers happen in people. Normally, the human body seeks homeostasis. That's a kind of balance in all its systems, and there are set points for temperature as well as hunger, thirst, and other mechanisms.

The hypothalamus is the part of your baby's brain that controls these operations, and it receives information from the body to help it adjust and keep that balance. It will send instructions to raise or lower the temperature for several reasons, and sometimes it's because your child is sick.

While the normal human body temperature is recognized at 98.6 degrees F (37 C), the truth is that it varies, depending on age, gender, time of day, activity level, and other reasons. A person's "normal" body temperature also may change over time. More than two dozen studies in recent years have found shifts in average human body temperature measured in decades, not hours.

Fever in Babies

Babies and children can have even larger variations in their "normal" temperature, so it's important to know what is actually considered a fever. Unless your child has an underlying medical condition and their healthcare provider has told you otherwise, a temperature is not considered a fever until it is over 100.4 F. But that's the highest acceptable level in babies 3 months old or younger.

If an infant is 3 months old or less and has a rectal temperature of 100.4 F (38 C) or higher, call your doctor or seek emergency care immediately. If your child is 3 to 12 months old and has a fever of 102.2 F (39 C) or higher, call your doctor for more guidance.

If you don't need to see a doctor and want to give medication, you should know that:

  • Newborns up to age 2 months should not be given fever-reducing medication.
  • Tylenol (acetaminophen) is safe for infants over 2 months old, but be careful with doses.
  • Motrin or Advil (ibuprofen) is safe for babies over 6 months old.
  • Do not give aspirin to a child.

You can also try fever-reducing techniques that don't involve medication, like taking off extra layers of clothing, giving lukewarm baths (not cold) and offering extra fluids. These actions can be appropriate for conditions that aren't considered serious, a few of which we'll look at next.

Common Conditions that Cause Fever

Viral Infections

Viruses are easily spread, especially among children, but are rarely serious, with some exceptions. Among the most common viral infections linked to fever in babies are:

  • Common cold: Adenovirus, non-COVID coronavirus and rhinovirus cause most colds.
  • Influenza: The flu is common, but it can cause high fevers that require a doctor's visit.
  • Gastroenteritis: Vomiting and diarrhea may come with fever and also cause dehydration.
  • Ear infections: These are common in children and may cause fever, but usually get better without treatment.
  • Croup: The distinctive cough and fever are most common in kids from 6 months to 3 years of age.
  • Respiratory syncytial virus (RSV): With its cold and flu-like symptoms, RSV can be life-threatening in premature babies. It is also the most common cause of pneumonia in children younger than 1 year.

Bacterial Infections

Bacterial infections usually cause minor illnesses such as strep throat and ear infections, but an associated fever can signal a life-threatening condition like meningitis. These infections also include salmonella and Escherichia coli (E. coli), tuberculosis, and the antibiotic-resistant MRSA.

A 2021 study found E. coli, commonly associated with feces (poop), was the most common cause of severe bacterial infection in newborns with high fevers who went to the emergency room.

Like viral infections, bacterial infections have other symptoms besides fever—and your baby can't tell you if their throat is sore or their stomach hurts. Watch for vomiting and diarrhea along with a lack of appetite, because the dehydration that results can contribute to a fever, especially in newborns.

Vaccine Reactions

Babies sometimes get fevers after vaccinations, including the DTaP (diphtheria, pertussis, tetanus) immunization. A low-grade fever is common and it's less serious than high fevers associated with the previous generation of DPT vaccines.

For example, it's recommended that babies get five different shots at their 4-month-old checkup. A mild fever associated with these immunizations usually can be treated with sponge baths and non-aspirin pain relievers.

Overheating

It may seem obvious, but your baby may have a slight fever because they're too warm! Babies, like elders, don't regulate their body temperatures as well as other people do. That's even more true in hot seasonal temperatures or in overheated winter rooms, and it's easy to fix. Remove clothing, move to a different room, make sure the baby has fluids, and try a sponge bath.

Overheating can be serious, though, and babies can experience heat exhaustion and heat stroke just as adults do. Overheating also is linked to a higher risk of Sudden Infant Death Syndrome.

Recap

Most causes of fever in babies are because of common infections or vaccine reactions, and often can be treated without calling a healthcare provider.


But it's also important to consider that bacterial infections like meningitis, or overheating that leads to heat stroke, can become life-threatening. It's important to look at the total picture and not just the thermometer if you think your baby may have a serious condition.

Serious Conditions

Some illnesses that cause fever in babies are serious and may be life-threatening. Some of the more common conditions may be acute (sudden onset) or chronic (long-lasting) health threats.

Meningitis

Meningitis is an infection of the tissues and fluid that cover the brain and spinal cord, and bacterial meningitis is potentially fatal. Babies with meningitis are irritable, don't eat well, and may be sleepy and difficult to wake. Infants with meningitis likely have a fever, and possibly a bulging or swelling at the fontanelle (soft spot on head).

Other symptoms of meningitis in babies can include:

  • Jaundice (a yellowish tint to the skin)
  • Neck and body stiffness
  • Weakness when sucking

Call your doctor immediately for these symptoms. The doctor may want to do a spinal tap if meningitis is suspected.

Cancer

Persistent fevers, especially when the baby also has night sweats or very pale, waxy skin, are symptoms associated with childhood cancers. The most common kinds of cancer in very young children include neuroblastoma and leukemia, according to the American Academy of Pediatrics.

Kawasaki Disease

Kawasaki disease is an inflammation of the blood vessels. When left untreated, it is one of the top causes of heart problems that develop in childhood. A stubborn fever is a telltale sign of Kawasaki disease, which can affect all children but is more common in some Asian families. Other symptoms include swelling, skin peeling on the hands and feet, vomiting, and diarrhea.

Doctors aren't sure what causes this illness but it's highly treatable. They think it may be linked to genetics, environmental factors, and respiratory viruses.

Autoimmune Disorders

It's not as common, but fever in babies can be linked to autoimmune disorders. They include diseases like Type 1 diabetes and lupus, with fever being one of the earliest signs of lupus. Other causes may include allergic reactions to foods or medications.

Symptoms change depending on the underlying illness, but it's important to call your baby's doctor if you think that fever is part of a pattern of symptoms so it can be diagnosed right away.

When to Call the Doctor

Babies generally tolerate fevers well. However, for babies under 12 months old, call your doctor or 911 right away for a fever above:

  • 100.4 F if under 3 months
  • 102.2 F in babies aged 3 to 12 months

You should also call the doctor if your baby has a fever for more than 48 hours, even if it isn't very high, to see if your baby needs an appointment.

Other reasons to call may include:

  • Fever that comes and goes
  • Fever that lasts longer than three days
  • Fever with a febrile seizure
  • Fever with symptoms of meningitis
  • Fever with vomiting, diarrhea or inability to drink

Signs of a Seizure

Febrile seizures seem alarming but typically cause no harm to the child. Watch for body stiffening or shaking, eyes rolling back in the head, or loss of consciousness. If symptoms continue more than 15 minutes, call for help.

Summary

A baby's fever needs attention, if for no other reason than to make your child more comfortable. But it's not serious most of the time, and a fever is actually one way the body works to keep itself healthy. Antibiotics for an infection, or other medications, may help your baby, depending on the cause of the fever.

Sometimes a fever signals a true health threat, and along with other symptoms may suggest a serious illness like meningitis or cancer. Your child's pediatrician can help to determine if there is an underlying condition, and can order the tests needed for a diagnosis.

A Word From Verywell

Perhaps the most important thing to understand about fevers in babies (and kids of all ages) is to treat them based on how the child behaves, not the number on the thermometer. As long as the temperature doesn't meet one of the criteria listed above and your baby is acting normally (smiling or happy and playful), there is no need to be concerned.

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