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).
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). Rarely, a fever gets so high that children become listless, drowsy, and unresponsive.
(See also Fever in Adults.)
How to Take a Child’s Temperature
A child's temperature can be taken from the rectum, ear, mouth, forehead, or armpit. It can be taken with a digital thermometer. Digital thermometers are easier to use and give much quicker readings (and usually give a signal when they are ready). Glass thermometers containing mercury are no longer recommended because they can break and expose people to mercury. Rectal temperatures are most accurate. That is, they come closest to the child's true internal body temperature. For a rectal temperature, the bulb of the thermometer should be coated with a lubricant. Then the thermometer is gently inserted about 1/2 to 1 inch (about 1 1/4 to 2 1/2 centimeters) into the rectum while the child is lying face down. The child should be kept from moving. Oral temperatures are taken by placing a digital thermometer under the child's tongue. Oral temperatures provide reliable readings but are difficult to take in young children. Young children have difficulty keeping their mouth gently closed around the thermometer, which is necessary for an accurate reading. The age at which oral temperatures can be reliably taken varies from child to child but is typically after age 4. Armpit temperatures are taken by placing a digital thermometer in the child's armpit, directly on the skin. Doctors rarely use this method because it is less accurate than others (readings are usually too low and vary greatly). However, if caretakers are uncomfortable taking a rectal temperature and do not have a device to measure ear or forehead temperature, measuring armpit temperature may be better than not measuring temperature at all. Ear temperatures are taken with a digital device that measures infrared (heat) radiation from the eardrum. Ear thermometers are unreliable in infants under 3 months old. For an ear temperature, the thermometer probe is placed around the opening of the ear so that a seal is formed, then the start button is pressed. A digital readout provides the temperature. Forehead temperatures (temporal artery temperatures) are taken with a digital device that measures infrared radiation from an artery in the forehead (the temporal artery). For a forehead temperature, the head of the thermometer is moved lightly across the forehead from hairline to hairline while pressing the scan button. A digital readout provides the temperature. Forehead temperatures are not as accurate as rectal temperatures, particularly in infants under 3 months old. |
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 fever
Acute fevers in infants and children are usually caused by an infection. Teething does not typically cause fever over 101° F (38.3° C).
The most common causes of acute fever are
Respiratory infections due to a virus, such as colds or flu
Gastroenteritis (infection of the digestive tract) due to a virus
Certain bacterial infections, particularly ear infections (otitis media), sinus infections, pneumonia, and urinary tract infections
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 (a serious infection of the blood), pneumonia (infection of the small air sacs of the lungs), and meningitis (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). Unlike older children, they sometimes have bacteremia with no symptoms besides fever (called occult bacteremia). Routine vaccines against the bacteria that usually cause occult bacteremia (Streptococcus pneumoniae and Haemophilus influenzae type b [Hib]) 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) or joints (septic arthritis), viral or bacterial infections of the brain (encephalitis) or the tissues covering the brain (meningitis), or disorders where different parts of the body become inflamed (Kawasaki disease or multisystem inflammatory syndrome in children [MIS-C]). Heatstroke 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). 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
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
Abdominal abscesses (pockets of pus in the abdomen)
Infections of the digestive tract caused by bacteria or parasites
Bone infections (such as osteomyelitis)
Heart infections (such as endocarditis)
Noninfectious causes of chronic fever include
Juvenile idiopathic arthritis or other connective tissue disorders
Occasionally, children fake a fever, or caregivers fake a fever in the child they care for. 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.
Warning signs
Certain symptoms are cause for concern. They include
Any fever in infants less than 3 months old
Lethargy or listlessness
Ill appearance
Difficulty breathing
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).
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).
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.
Testing
The need for testing depends on the child's age, overall appearance, vaccination status, and whether the fever is acute or chronic. Doctors may also do testing for particular disorders they suspect ( see Table: 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). Doctors need to rule out a serious bacterial infection, such as meningitis, sepsis/bacteremia, or a urinary tract infection. 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 (lumbar puncture), and sometimes a chest x-ray. 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, 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. 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.
General measures
Ways to help children with a fever feel better without using drugs include
Giving children plenty of fluids to prevent dehydration
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).
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 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.
influenza or chickenpox) and cause a serious disorder called Reye syndrome.
Key Points
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 (about 38° C) 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.
