Normal body temperature varies from person to person and throughout the day (it is typically highest in the afternoon). Normal body temperature is higher in preschool-aged children and highest at about 18 to 24 months of age. However, despite these variations, most doctors define fever as a temperature of 100.4° F (about 38° C) or higher when measured with a rectal thermometer (see How to Take A Child's Temperature How to Take a Child’s Temperature ).
Although parents often worry about how high the temperature is, the height of the fever does not necessarily indicate how serious the cause is. Some minor illnesses cause a high fever, and some serious illnesses cause only a mild fever. Other symptoms (such as difficulty breathing, confusion, and not drinking) indicate the severity of illness much better than the temperature does. However, a temperature over 106° F (about 41° C), although quite rare, can itself be dangerous.
Fever can be useful in helping the body fight infection. Some experts think that reducing fever can prolong some disorders or possibly interfere with the immune system's response to infection. Thus, although a fever is uncomfortable, it does not always require treatment in otherwise healthy children. However, in children with a lung, heart, or brain disorder, fever may cause problems because it increases demands on the body (for example, by increasing the heart rate). So lowering the temperature in such children is important.
Infants with a fever are usually irritable and may not sleep or feed well. Older children lose their interest in play. Usually, the higher a fever gets, the more irritable and disinterested children become. However, sometimes children with a high fever look surprisingly well. Children may have seizures when their temperature rises or falls rapidly (called febrile seizures Febrile Seizures Febrile seizures are seizures triggered by a fever of at least 100.4° F (about 38° C). Most febrile seizures are harmless and caused by fever from a minor infection. Less often, a febrile seizure... read more ). Rarely, a fever gets so high that children become listless, drowsy, and unresponsive.
(See also Fever in Adults Fever in Adults Fever is an elevated body temperature that occurs when the body's thermostat (located in the hypothalamus in the brain) resets at a higher temperature, primarily in response to an infection... read more .)
Causes of Fever in Infants and Children
Fever occurs in response to infection, injury, or inflammation and has many causes. Likely causes of fever depend on whether it has lasted 14 days or less (acute) or more than 14 days (chronic), as well as on the age of the child. Fevers are usually acute.
Acute fevers in infants and children are usually caused by an infection. Teething Teething A child's first tooth usually appears by 6 months of age, and a complete set of 20 primary or first teeth usually develops by 2½ years. Before a tooth appears, the child may cry, be fussy, and... read more does not typically cause fever over 101° F.
The most common causes of acute fever are
Respiratory infections due to a virus, such as colds or flu
Certain bacterial infections, particularly ear infections Acute Middle Ear Infection in Children Acute middle ear infection is a bacterial or viral infection of the middle ear, usually accompanying a cold. Bacteria and viruses can infect the middle ear. Children with ear infections may... read more (otitis media), sinus infections, pneumonia Overview of Pneumonia Pneumonia is an infection of the small air sacs of the lungs (alveoli) and the tissues around them. Pneumonia is one of the most common causes of death worldwide. Often, pneumonia is the final... read more , and urinary tract infections Urinary Tract Infection (UTI) in Children A urinary tract infection is a bacterial infection of the urinary bladder ( cystitis), the kidneys ( pyelonephritis), or both. Urinary tract infections are caused by bacteria. Infants and younger... read more
Newborns and young infants are at higher risk of certain serious infections because their immune system is not fully developed. Such infections may be acquired before birth or during birth and include sepsis Sepsis in Newborns Sepsis is a serious bodywide reaction to infection spread through the blood. Newborns with sepsis appear generally ill—they are listless, do not feed well, often have a gray color, and may have... read more (a serious infection of the blood), pneumonia (infection of the small air sacs of the lungs), and meningitis Meningitis in Children Bacterial meningitis is a serious infection of the layers of tissue covering the brain and spinal cord ( meninges). Bacterial meningitis in older infants and children usually results from bacteria... read more (infection of the tissues covering the brain).
Children under 3 years old who develop a fever (particularly if their temperature is 102.2° F [39° C] or higher) sometimes have bacteria in their bloodstream (bacteremia Bacteremia Bacteremia is the presence of bacteria in the bloodstream. Bacteremia may result from ordinary activities (such as vigorous toothbrushing), dental or medical procedures, or from infections ... read more ). Unlike older children, they sometimes have bacteremia with no symptoms besides fever (called occult bacteremia Occult Bacteremia Occult (hidden) bacteremia is the presence of bacteria in the bloodstream of a child who has a fever but who looks well and has no obvious source of infection. Most commonly, occult bacteremia... read more ). Routine vaccines Childhood Vaccination Schedule Most doctors follow the vaccination schedule recommended by the Centers for Disease Control and Prevention (CDC—see the schedule for infants and children and the schedule for older children... read more against the bacteria that usually cause occult bacteremia (Streptococcus pneumoniae Pneumococcal Vaccine Pneumococcal vaccines help protect against bacterial infections caused by Streptococcus pneumoniae (pneumococci). Pneumococcal infections include ear infections, sinusitis, pneumonia... read more and Haemophilus influenzae type b [Hib] Haemophilus influenzae Type b Vaccine The Haemophilus influenzae type b (Hib) vaccine helps protect against bacterial infections due to Hib, such as pneumonia and meningitis. These infections may be serious in children. Use... read more ) are now widely used in the United States and Europe. As a result, these vaccines have nearly eliminated occult bacteremia in children in this age group.
Less common causes of acute fever include side effects of vaccinations and of certain drugs, bacterial infections of the skin (cellulitis Cellulitis Cellulitis is a spreading bacterial infection of the skin and the tissues immediately beneath the skin. This infection is most often caused by streptococci or staphylococci. Redness, pain, and... read more ) or joints (septic arthritis Infectious Arthritis Infectious arthritis is infection in the fluid and tissues of a joint usually caused by bacteria but occasionally by viruses or fungi. Bacteria, viruses, or fungi may spread through the bloodstream... read more ), viral or bacterial infections of the brain (encephalitis Encephalitis Encephalitis is inflammation of the brain that occurs when a virus directly infects the brain or when a virus, vaccine, or something else triggers inflammation. The spinal cord may also be involved... read more ) or the tissues covering the brain (meningitis Meningitis in Children Bacterial meningitis is a serious infection of the layers of tissue covering the brain and spinal cord ( meninges). Bacterial meningitis in older infants and children usually results from bacteria... read more ), or disorders where different parts of the body become inflamed (Kawasaki disease Kawasaki Disease Kawasaki disease causes inflammation of blood vessels throughout the body. The cause of Kawasaki disease is unknown but may be associated with an infection. Children typically have fever, rash... read more or multisystem inflammatory syndrome in children Complications COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more [MIS-C]). Heatstroke Heatstroke Heatstroke is a life-threatening condition that results in very high body temperature and malfunction of many organ systems. (See also Overview of Heat Disorders.) Heatstroke can develop after... read more causes a very high body temperature.
Typically, a fever due to vaccination lasts a few hours to a day after the vaccine is given. However, some vaccinations can cause a fever even 1 or 2 weeks after the vaccine is given (as with measles vaccination Side Effects The measles, mumps, and rubella (MMR) vaccine is a combination vaccine that helps protect against these three serious viral infections. The vaccine contains live but weakened measles, mumps... read more ). Children who have a fever when they are scheduled to receive a vaccine can still receive the vaccine if the fever is low and they have no serious illness.
Chronic fever most commonly results from
A prolonged viral illness
Back-to-back viral illnesses, especially in young children
Chronic fever can also be caused by many other infectious and noninfectious disorders.
Infectious causes of chronic fever include
Infections of the digestive tract caused by bacteria or parasites
Noninfectious causes of chronic fever include
Juvenile idiopathic arthritis or other connective tissue disorders
Cancer (such as leukemia Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more and lymphoma Overview of Lymphoma Lymphomas are cancers of lymphocytes, which reside in the lymphatic system and in blood-forming organs. Lymphomas are cancers of a specific type of white blood cells known as lymphocytes. These... read more )
Occasionally, children fake a fever, or caregivers fake a fever in the child they care for Factitious Disorder Imposed on Another Factitious disorder imposed on another is falsifying or producing symptoms of a physical or psychologic disorder in another person. It is usually done by caregivers (typically parents) to someone... read more . Sometimes the cause is not identified.
Evaluation of Fever in Infants and Children
Detecting a fever is not difficult, but determining its cause can be.
Certain symptoms are cause for concern. They include
Any fever in infants less than 3 months old
Lethargy or listlessness
Bleeding in the skin, appearing as tiny reddish purple dots (petechiae) or splotches (purpura)
Continuous crying in an infant or toddler (inconsolability)
Headache, neck stiffness, confusion, or a combination in an older child
When to see a doctor
Children with fever should be evaluated by a doctor right away if they have any warning signs or are less than 3 months old.
Children without warning signs who are between 3 months and 3 years of age should be seen by the doctor if the fever is 102.2° F (39° C) or higher, if there is no obvious upper respiratory infection (that is, children are sneezing and/or have a runny nose and nasal congestion), or if the fever has continued more than 5 days.
For children without warning signs who are over 3 years of age, the need for and timing of a doctor's evaluation depend on the child's symptoms. Children who have upper respiratory symptoms but otherwise appear well may not need further evaluation. Children over 3 years of age with fever lasting more than 5 days should be seen by the doctor.
What the doctor does
Doctors first ask questions about the child's symptoms and medical history. Doctors then do a physical examination. A description of the child's symptoms and a thorough examination usually enable doctors to identify the fever’s cause ( see Table: Some Common Causes and Features of Fever in Children Some Common Causes and Features of Fever in Children ).
Doctors take the child’s temperature. It is measured rectally in infants and young children for accuracy. The breathing rate is noted. If children appear ill, blood pressure is measured. If children have a cough or breathing problems, a sensor is clipped on a finger or an earlobe to measure the oxygen concentration in blood (pulse oximetry Pulse oximetry Both arterial blood gas testing and pulse oximetry measure the amount of oxygen in the blood, which helps determine how well the lungs are functioning. Arterial blood gas tests are invasive... read more ).
As doctors examine children, they look for warning signs (such as an ill appearance, lethargy, listlessness, and inconsolability), noting particularly how children respond to being examined—for example, whether children are listless and passive or extremely irritable.
Occasionally, the fever itself can cause children to have some of the warning signs including lethargy, listlessness, and ill appearance. Doctors may give children fever-reducing drugs (such as ibuprofen) and reevaluate them once the fever is reduced. It is reassuring when lethargic children become active and playful once the fever is reduced. On the other hand, it is worrisome when ill-appearing children remain ill-appearing despite a normal temperature.
The need for testing depends on the child's age, overall appearance, vaccination status, and whether the fever is acute Testing for Acute Fever Normal body temperature varies from person to person and throughout the day (it is typically highest in the afternoon). Normal body temperature is higher in preschool-aged children and highest... read more or chronic Testing for Chronic Fever Normal body temperature varies from person to person and throughout the day (it is typically highest in the afternoon). Normal body temperature is higher in preschool-aged children and highest... read more . Doctors may also do testing for particular disorders they suspect ( see Table: Some Common Causes and Features of Fever in Children Some Common Causes and Features of Fever in Children ).
Testing for Acute Fever
For acute fever, doctors test for infectious causes according to the age of the child. They thoroughly evaluate children who are under 3 years of age, even those who do not look very ill and those who seem to have a source of infection (for example, an ear infection Acute Middle Ear Infection in Children Acute middle ear infection is a bacterial or viral infection of the middle ear, usually accompanying a cold. Bacteria and viruses can infect the middle ear. Children with ear infections may... read more ). Doctors need to rule out a serious bacterial infection, such as meningitis Meningitis in Children Bacterial meningitis is a serious infection of the layers of tissue covering the brain and spinal cord ( meninges). Bacterial meningitis in older infants and children usually results from bacteria... read more , sepsis/bacteremia Occult Bacteremia Occult (hidden) bacteremia is the presence of bacteria in the bloodstream of a child who has a fever but who looks well and has no obvious source of infection. Most commonly, occult bacteremia... read more , or a urinary tract infection Urinary Tract Infection (UTI) in Children A urinary tract infection is a bacterial infection of the urinary bladder ( cystitis), the kidneys ( pyelonephritis), or both. Urinary tract infections are caused by bacteria. Infants and younger... read more . Testing is especially necessary in infants, because the source of their fever is difficult to determine and because their immature immune system puts them at high risk of serious infection.
Fever in infants under 1 month old
Children in this age group who have a fever are hospitalized for testing and treatment because their risk of having a serious infection is high. Testing typically includes blood and urine tests, a spinal tap Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more (lumbar puncture), and sometimes a chest x-ray Chest Imaging Chest imaging studies include X-rays Computed tomography (CT) CT angiography Magnetic resonance imaging (MRI) read more . Stool tests are done in newborns who have diarrhea.
Fever in infants between 1 month and 3 months old
Children with fever in this age group who look ill (that is, who have an abnormal cry, lethargy, or other unusual behavior) or who have risk factors for a serious bacterial infection (that is, who have severe birth defects, were preterm, or are unvaccinated) should be hospitalized. These children undergo blood tests, urine tests, a chest x-ray, and a spinal tap to look for bacteremia, urinary tract infections, and meningitis.
Children with fever in this age group who look well also undergo blood and urine tests, but might not have a spinal tap. They are sometimes not admitted to the hospital.
Fever in children between 3 months and 3 years old
Children in this age group who have a fever but look well and can be watched closely may not need tests, especially if doctors find a source of the fever. If symptoms suggest a specific infection, doctors do the appropriate tests.
If children have no symptoms suggesting a specific disorder but look ill, have risk factors for a serious bacterial infection, or have a temperature of 102.2° F [39° C] or higher), blood and urine tests are usually done. Sometimes a spinal tap is done.
The need for hospitalization depends on how well or ill children look, the results of any tests done, and whether a follow-up examination can be done in a timely fashion.
Fever in children over 3 years old
Children in this age group do not typically undergo tests unless they have specific symptoms suggesting a serious disorder or if no source of the fever can be found.
Testing for Chronic Fever
For chronic fever, tests are often done. If doctors suspect a particular disorder, tests for that disorder are done. If the cause is unclear, screening tests are done. Screening tests include a complete blood cell count Complete blood count Doctors select tests to help diagnose blood disorders based on the person's symptoms and the results of the physical examination. Sometimes a blood disorder causes no symptoms but is discovered... read more , urinalysis and culture, and blood tests to check for inflammation. Tests for inflammation include the erythrocyte sedimentation rate (ESR) and measurement of C-reactive protein (CRP) levels. Other tests doctors sometimes do when there is no clear cause include stool tests, blood cultures or tests of antibody levels in the blood to detect bacteria or viruses, tuberculosis skin test or interferon-gamma release assay, chest x-rays, computed tomography (CT) of the sinuses, and bone scans.
Rarely, fevers persist, and doctors cannot identify the cause even after extensive testing. This type of fever is called fever of unknown origin Fever of unknown origin (FUO) Fever is an elevated body temperature that occurs when the body's thermostat (located in the hypothalamus in the brain) resets at a higher temperature, primarily in response to an infection... read more . Children with a fever of unknown origin may require additional testing and evaluation.
Treatment of Fever in Infants and Children
If the fever results from a disorder, that disorder is treated. Other fever treatment is focused on making children feel better.
Ways to help children with a fever feel better without using drugs include
Putting cool, wet cloths (compresses) on their forehead, wrists, and calves
Placing children in a warm bath (only slightly cooler than the temperature of the child)
Because shivering may actually raise the child’s temperature, methods that may cause shivering, such as undressing and cold baths, should not be used.
Rubbing the child down with alcohol or witch hazel must not be done because alcohol can be absorbed through the skin and cause harm. There are many other unhelpful folk remedies, ranging from the harmless (for example, putting onions or potatoes in the child's socks) to the uncomfortable and possibly harmful (for example, coining or cupping Cupping Cupping (a manipulative and body-based practice) is used in traditional Chinese medicine. Cupping is believed to increase blood flow to the area on which a cup is placed, thereby improving healing... read more ).
Drugs to lower fever
Fever in an otherwise healthy child does not necessarily require treatment. However, drugs called antipyretic (fever-lowering) drugs may make children feel better by lowering the temperature. These drugs do not have any effect on an infection or other disorder causing the fever. However, if children have certain chronic disorders or a history of seizures triggered by fever, using these drugs may be recommended by the doctor because they reduce the extra stress put on the body by fever.
Typically, the following drugs are used:
Acetaminophen, given by mouth or by suppository
Ibuprofen, given by mouth
Acetaminophen tends to be preferred. Ibuprofen, if used for a long time, can irritate the stomach’s lining. These drugs are available over the counter without a prescription. The recommended dosage is listed on the package or may be specified by the doctor. It is important to give the correct dose at the correct interval. The drugs do not work if too little drug is given or it is not given often enough. And although these drugs are relatively safe, giving too much of the drug or giving it too often can cause an overdose.
Rarely, acetaminophen or ibuprofen is given to prevent a fever, as when infants have just been vaccinated.
Aspirin is no longer used for lowering fever in children because it can interact with certain viral infections (such as influenza Influenza (Flu) Influenza (flu) is a viral infection of the lungs and airways with one of the influenza viruses. It causes a fever, runny nose, sore throat, cough, headache, muscle aches (myalgias), and a general... read more or chickenpox Chickenpox Chickenpox is a highly contagious viral infection with the varicella-zoster virus that causes a characteristic itchy rash, consisting of small, raised, blistered, or crusted spots. Chickenpox... read more ) and cause a serious disorder called Reye syndrome Reye Syndrome Reye syndrome is a very rare but life-threatening disorder that causes inflammation and swelling of the brain and impairment and loss of function of the liver. The cause of Reye syndrome is... read more .
Usually, fever is caused by a viral infection.
The likely causes of fever and need for testing depend on the age of the child.
Infants under 3 months of age with a temperature of 100.4° F or higher need to be evaluated promptly by a doctor.
Children age 3 months to 3 years with fever who have no symptoms suggesting a specific disorder but who look ill or have a temperature of 102.2° F (39° C) or higher need to be evaluated promptly by a doctor.
Teething does not cause significant fever.
Drugs that lower fever may make children feel better but do not affect the disorder causing the fever.