By Kristina Herndon, RN 

 Medically reviewed by Lyndsey Garbi, MD

There are many reasons why your baby may have a fever—even teething can cause tiny rises in temperature—and most of the causes aren't life-threatening.

Fever is normally a sign that the body is fighting an infection to stay healthy. But a young baby's fever can be concerning, especially if your child has other symptoms. There are times when a fever and related symptoms may signal a true emergency, so 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.

What Causes Fever

The normal human body temperature is recognized at 98.6 degrees F (37 C).

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

Fever in Babies

Babies and children can have mild variations in their "normal" temperature, so it's important to know what is actually considered a fever. Unless your child's healthcare provider has told you otherwise, a high temperature is not considered a fever until it is over 100.4 F.1

If your baby has a fever of 100.4 F (38 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:

• Tylenol (acetaminophen) is safe for infants, 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. Viral infections are rarely serious, with some exceptions.

Among the most common viral infections linked to fever in babies:

• 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 the most common cause of bronchiolitis in children younger than 1 year.2

Bacterial Infections

Bacterial infections usually cause minor illnesses such as strep throat and ear infections.

An associated fever can signal a more serious bacterial infection, like salmonella, Escherichia coli (E. coli), tuberculosis, and the antibiotic-resistant MRSA. And meningitis (inflammation of the tissue surrounding the brain) can be viral, but bacterial forms of meningitis can be life-threatening.

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.3

Like viral infections, bacterial infections have other symptoms besides fever. Since your baby can't tell you if their throat is sore or their stomach hurts, watch for vomiting, diarrhea, or a lack of appetite. Dehydration can be a complication of these types of infections.

Vaccine Reactions

Babies sometimes get fevers after vaccinations,4 including the DTaP (diphtheria, pertussis, tetanus) immunization. A low-grade fever is common, and it's not considered serious.

A mild fever associated with immunizations usually can be treated with sponge baths and non-aspirin pain relievers.5

Overheating

It may seem obvious, but your baby may have a slight fever because they're too warm! Babies don't regulate their body temperatures as well as older children and adults. That's especially 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 it can cause heat exhaustion and heat stroke. Overheating also is linked to a higher risk of Sudden Infant Death Syndrome (SIDs).6

Most causes of fever in babies are because of common infections or vaccine reactions.

But it's also 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.

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 sleepy. Infants with meningitis likely have a fever, and possibly a bulging or swelling at the fontanelle (soft spot on head).7

Other symptoms of meningitis in babies can include:

• Jaundice (a yellowish tint to the skin)

• Neck and body stiffness

• Weakness when sucking

• Lethargy

• Low body temperature

Call your doctor immediately if your baby develops symptoms. The doctor may need 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.8

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 and is more common in some Asian families. Other symptoms include swelling, skin peeling on the hands and feet, vomiting, and diarrhea.

The cause of this illness is not known, but it's highly treatable. It may be linked to genetics, environmental factors, and respiratory viruses.9

Autoimmune Disorders

It's not as common, but fever in babies can be linked to autoimmune disorders.10 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 fever above 100.4 F.

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 seizure11

• Fever with symptoms of meningitis

• Fever with vomiting, diarrhea, or decreased intake of fluids

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.12

Summary

A baby's fever needs attention, primarily to make your child more comfortable. But it's not serious most of the time, and fever is actually one way the body works to keep itself healthy. Antibiotics for the treatment of a bacterial infection or other medications may help your baby, depending on the cause of the fever.

Sometimes a fever signals a true health threat, especially if it comes with other symptoms. Your child's pediatrician can help to determine if your child's fever requires further evaluation and medical treatment.

 Sources

Nemours Foundation. Fevers. Updated September 2018.

Centers for Disease Control and Prevention. Symptoms and care of RSV. Updated December 18, 2020.

Chen Y-T, Chang Y-J, Liu B-Y, Lee E-P, Wu H-P. Severe bacterial infection in young infants with pyrexia admitted to the emergency department. Medicine. 2021;100(27):e26596. doi: 10.1097/MD.0000000000026596

Office of Infectious Disease and HIV/AIDS Policy. Vaccine side effects. Updated April 29, 2021.

Centers for Disease Control and Prevention. Baby Vaccines at 4 months. Updated February 25, 2020.

Margolis HG. Heat waves and rising temperatures: human health impacts and the determinants of vulnerability. In: Pinkerton KE, Rom WN, eds. Climate Change and Global Public Health. Springer International Publishing; 2021:123-161. doi: 10.1007/978-3-030-54746-2_7

Nemours Foundation. Meningitis (for Parents). Updated May 2021.

American Academy of Pediatrics. Types of childhood and adolescent cancers. Updated September 12, 2019.

Banday AZ, Arul A, Vignesh P, Singh MP, Goyal K, Singh S. Kawasaki disease and influenza—new lessons from old associations. Clin Rheumatol. 2021;40(7):2991-2999. doi: 10.1007/s10067-020-05534-1

Institute for Quality and Efficiency in Health Care, Cologne, Germany. Fever in children: Overview. Updated June 6, 2019.

Seinfeld S, Shinnar S. Febrile seizures. Swaimans Pediatric Neurology. 2017:519-523. doi:10.1016/b978-0-323-37101-8.00065-5

NIH National Institute of Neurological Disorders and Stroke. Febrile seizures fact sheet. Updated March 16, 2020.

Additional Reading

American Academy of Pediatrics.Fever and your baby. Updated July 19, 2021.

By Kristina Herndon, RN
Kristina Herndon, BSN, RN, CPN, has been working in healthcare since 2002. She specializes in pediatrics and disease and infection prevention.