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.
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 (febrile seizures—see Febrile Seizures). Rarely, a fever gets so high that children become listless, drowsy, and unresponsive.
Fever occurs in response to infection, injury, or inflammation and has many causes. Likely causes of fever depend on whether it has lasted 7 days or less (acute) or more than 7 days (chronic), as well as on the age of the child.
Acute fevers in infants and children are usually caused by an infection. Teething does not typically cause fever over 101° F.
The most common causes are
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 bodywide infection), pneumonia, and meningitis.
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—see Occult Bacteremia). 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, occult bacteremia is less common. However, pneumococcal strains that are not a part of the current pneumococcal vaccine or other bacteria can sometimes cause it.
Less common causes of acute fevers include side effects of vaccinations and of certain drugs, bacterial infections of the skin (cellulitis) or joints (septic arthritis), and viral or bacterial infections of the brain (encephalitis), the tissues covering the brain (meningitis), or both. 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.
Chronic fever most commonly results from
Chronic fever can also be caused by many other infectious and noninfectious disorders. Infectious causes include hepatitis, sinusitis, pneumonia, pockets of pus (abscesses) in the abdomen, infections of the digestive tract caused by bacteria or parasites, bone infections (osteomyelitis), heart infections (endocarditis), and tuberculosis. Noninfectious causes include Kawasaki disease, inflammatory bowel disease, juvenile idiopathic arthritis or other connective tissue disorders, and cancer (such as leukemia and lymphoma). Occasionally, children fake a fever, or caregivers fake a fever in the child they care for. Sometimes the cause is not identified.
Detecting a fever is not difficult, but determining its cause can be.
Certain symptoms are cause for concern. They include
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 2 months old.
Children without warning signs who are between 3 months and 36 months old 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 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 36 months old, 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 36 months 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 5: 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.
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.
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For acute fever, doctors can often make a diagnosis without testing. For example, if children do not appear very ill, the cause is usually a viral infection; a respiratory infection if they have a runny nose, wheezing, or a cough; or gastroenteritis if they have diarrhea and vomiting. In such children, the diagnosis is clear, and testing is not needed. Even if no specific symptoms suggest a diagnosis, the cause is still often a viral infection in children who otherwise do not appear very ill. Doctors try to limit testing to children who may have a more serious disorder. The chance of a serious disorder (and thus the need for tests) depends on the child's age, symptoms, and overall appearance, plus the particular disorders the doctor suspects (see Table 5: Some Common Causes and Features of Fever in Children).
If newborns (28 days old or younger) have a fever, they are hospitalized for testing because their risk of having a serious infection is high. Testing typically includes blood and urine tests, a spinal tap (lumbar puncture—see Spinal Tap), and sometimes a chest x-ray.
In infants between 1 month and 3 months old, blood tests and urine tests (urinalysis) and cultures are done. The need for hospitalization, a chest x-ray, and a spinal tap depends on results of the examination and blood and urine tests, as well as how ill or well infants appear and whether a follow-up examination can be done. Testing in infants under 3 months old is done to look for occult bacteremia, urinary tract infections, and meningitis. Testing is necessary because the source of fever is difficult to determine in infants and because their immature immune system puts them a high risk of serious infection.
If children aged 3 to 36 months look well and can be watched closely, tests are not needed. If symptoms suggest a specific infection, doctors do the appropriate tests. If children have no symptoms suggesting a specific disorder but look ill or have a temperature of 102.2° F (39° C) or higher, blood and urine tests are usually done. The need for hospitalization depends on how well or ill children look and whether a follow-up examination can be done.
In children over 36 months old, tests are typically not done unless children have specific symptoms suggesting a serious disorder.
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, tuberculosis tests, chest x-rays, and computed tomography (CT) of the sinuses.
Rarely, fevers persist, and doctors cannot identify the cause even after extensive testing. This type of fever is called fever of unknown origin (see Testing). Children with a fever of unknown origin are much less likely to have a serious disorder than are adults.
If the fever results from a disorder, that disorder is treated. Other treatment focuses on making children feel better.
Ways to help children with a fever feel better without using drugs include
Because shivering may actually raise the child's temperature, methods that may cause shivering, such as undressing and cool baths, should be used only for dangerously high temperatures of 106° F (about 41° C) and above.
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 (for example, coining or cupping).
Drugs to lower fever:
Fever in an otherwise healthy child does not necessarily require treatment. However, drugs called antipyretic 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 a heart, lung, brain, or nerve disorder or a history of seizures triggered by fever, using these drugs is important because they reduce the extra stress put on the body by fever.
Typically, the following drugs are used:
Acetaminophen tends to be preferred. However, some doctors are concerned that acetaminophen use has contributed to the recent increase in asthma in children and thus do not recommend its use in children with asthma or who have a family history of asthma. 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 been vaccinated.
Aspirin is no longer used for lowering fever in children because it can interact with certain viral infections (such as influenza or chickenpox) and cause a serious disorder called Reye syndrome (see Reye Syndrome).
Last full review/revision February 2013 by Deborah M. Consolini, MD