Fever in Children

 Where Does Fever Come From?

 How Do I Measure Temperature?

 What Should I Worry About? When Should I Call My Doctor?
 What Other Symptoms Typically Accompany Fever?
 What Types of Illnesses Cause Fever, and What Are Their Specific Symptoms?
 How Do I Treat Fever?
 Is There a Downside to Treating a Fever?
 What Might the Doctor Do?
How Do I Prevent Fever?

          Fever in children can provoke tremendous anxiety in parents.  Children with fever are hot, sweaty, flushed, and fussy.  In healthy children, however, fevers rarely indicate serious illness.  In fact, fever is a way your child’s body actually fights infections.  It is not even necessary always to treat fever in children.  High fevers, however, make children increasingly uncomfortable and may cause irritability and dehydration.

Normal body temperature is usually cited as 98.6 degrees Fahrenheit, as measured by a thermometer placed under the tongue (“oral temperature”).  “Normal” temperature varies in children by 1-1.5 degrees throughout the day and according to their level of activity; it is usually lowest early in the morning and highest in late afternoon.  Fever is an elevation of body temperature above that normal range. Fever is defined as a rectal temperature greater than 100.4 degrees Fahrenheit, an oral temperature greater than 99.5 degrees Fahrenheit, or an axillary temp greater than 99 degrees Fahrenheit.  Children under 2 months of age should always be evaluated by a physician for temperature above 100.4 degrees measured rectally.  Fever is the human body’s normal and healthy reaction to infection and is caused by a complex chain of biochemical and cellular reactions that are launched to fight that infection.  Elevation of a child’s body temperature associated with active play or with exposure to hot weather is not considered a fever.

          Fever is a symptom, not a disease.  The magnitude of fever does not

necessarily correlate to the severity of infection, as fever may be very high with a brief viral illness and lower (or sometimes the body temperature is actually abnormally low) in the face of a life-threatening infection.  It is generally felt that a fever up to around 102 degrees Fahrenheit (oral) can help the body fight the infection, although as stated above this does not apply to children under two months of age  In general, children have higher fevers than adults (1).  This Knol discusses fever in children; fever in adults is discussed separately.


Fever in Children

Where Does Fever Come From?

          Body temperature is controlled by a small organ deep in the brain called thehypothalamus (FIGURE 1).  The hypothalamus controls metabolic processes in the body (such as body temperature, hunger, thirst, fatigue, and stress reactions) by releasing tiny amounts of chemicals that act on other body organs either directly or indirectly.  With respect to body temperature, the hypothalamus acts as a thermostat; it helps maintain body warmth when someone is exposed to cold temperatures by causing shivering and an increased metabolic rate.  When a child is hot (from a fever, from exercise, or from hot weather), it causes sweating and dilation (opening up) of blood vessels in the skin, allowing dissipation of heat. 

          Fever results when the hypothalamus detects the presence of pyrogens, or fever-inducing substances. Pyrogens are usually foreign substances to your child’s body, such as bacteria, viruses, parasites, immunizations, or toxins.  The presence of these pyrogens activates other “native” (not foreign) infection-fighting pyrogens such as white blood cells inside the body, and the accumulation of these substances signals the hypothalamus to raise the temperature on the body’s thermostat.  In response, the child feels cold and his body shivers, blood vessels in the skin constrict (tighten down) to retain heat, and he seeks warm clothing or bed covers, all in an attempt to reach the new target temperature on the thermostat.  That new, higher temperature represents a higher metabolic level for the body, assisting the child’s fight against the infection.

          Once the higher temperature is reached, the child begins to feel hot.  Clothing and bed covers are shed, and the temperature begins to drop back towards normal.  The child may begin to sweat and the blood vessels in the skin dilate, leading to rosy cheeks and release of heat.  Fever medications, also called “anti-pyretics” such as acetaminophen and ibuprofen, work by interfering with the function of the hypothalamus.  These drugs therefore inhibit the body’s natural response to infection (see “Is There a Downside to Treating a Fever?,” below).


How Do I Measure Temperature?

          Body temperature can be measured by glass thermometers or plastic analog or digital thermometers placed under the tongue (oral), into the rectum (rectal), or into the armpit (axillary) with the arm held tightly against the torso.  There are also digital thermometers that measure temperature inside the ear (tympanic), plastic strip thermometers that measure the temperature on the forehead, and pacifier thermometers that measure an above-the-tongue oral temperature.  Axillary temperatures are not considered reliable by physicians, but may give caregivers an idea of the magnitude of fever if they are uncomfortable obtaining a rectal temperature.  In very young children, particularly infants in whom an accurate temperature reading is important, tympanic, forehead, and pacifier temperature are not optimal.  Rectal temperature is closer to the body’s true “core” temperature.  Generally, rectal temperatures are preferred in children under 2-3 years of age; oral temps are preferred thereafter. 

Rectal temps are obtained by inserting a petrolatum-coated thermometer about a half-inch inside the rectum; stop if any resistance is felt. Hold the rectal thermometer there until the temperature is taken; depending on the thermometer, this may take only a few seconds or as long as a couple of minutes.  If the child is moving, it is important to hold the thermometer between the second and third fingers, with the hand resting on the buttock, so that the probe doesn’t go too deep if the child squirms (FIGURE 2).  Oral temperature is measured by placing the thermometer under the tongue, and holding it there for 2-3 minutes (or until a digital thermometer signals that it is ready) without talking and preferably while breathing through the nose; this may be difficult in a child who is coughing or who is mouth-breathing because of nasal congestion. Avoid measuring oral temperature within 15 minutes after drinking a hot or cold beverage, or just after a bath. Rectal temperatures are always about one degree higher than oral temps, and a fever is defined as a rectal temperature greater than 100.4 degrees Fahrenheit, an oral temperature greater than 99.5 degrees Fahrenheit, or an axillary temp greater than 99 degrees Fahrenheit. 

          If no thermometer is available, feeling the skin temperature on the forehead or the side of the neck may give a relative sense of whether or not fever is present.  Flushing of the skin, shaking chills, fatigue, perspiration, and lethargy or fussiness often accompany fever and may be suggestive in the absence of actual temperature measurement.


What Should I Worry About? When Should I Call My Doctor?

          Children under 2 months of age should be evaluated by a physician for any fever.  Older children should be evaluated by a physician for a temperature higher than 102.2 degrees Fahrenheit, or when fever is accompanied by one of the following conditions:


  • seizure
  • inconsolable crying or irritability
  • rash or purple spots that look like bruises on the skin (FIGURE 3, photo reproduced with permission of Annals of Emergency Medicine)
  • bluish tinge around the lips or finger- and toenails
  • stiff neck or severe headache
  • difficulty breathing that does not improve after clearing the nose
  • leaning forward and drooling
  • persistent vomiting or diarrhea
  • signs of dehydration (small amounts or no urination, no tears when crying, listless or drowsiness) and not taking oral fluids well
  • a specific, localized complaint, such as an earache, sore throat, abdominal pain, or pain with urination
  • in infants, a swelling or noticeable sinking of the soft spot at the top of the head
  • sore or swollen joints
  • fever developed after child was left in a very hot environment, including an automobile
  • fever that persists for more than 24 hours in children 2 mos-2 years of age, or for more than 72 hours in children over 2, or fever that comes and goes over several days

In the absence of these conditions, and in children who are fully vaccinated and do not have chronic health problems, parents can try to manage fever at home with antipyretics, rest, and hydration.


What Other Symptoms Typically Accompany Fever?

          Physicians often determine the approach to fever based on the child’s age.  There are three age groups with respect to the concern physicians have for a fever: age 1-30 days, age 1-24 months, and age greater than two years (2,3).  Neonates (a term used for patients less than one month of age) have very immature immune systems and are exposed to a variety of infections uncommon in older children.  Children more than one month but less than two years old may require a more intensive evaluation for fever than older children.  Beyond age two, children increasingly resemble adults in terms of the fevers they develop in response to exposure to infections, drugs, and toxins.

Common general symptoms accompanying a fever in children include flushing/redness, profuse perspiration, irritability, fatigue, and lethargy.  More so than in adults, the rate at which the temperature rises in ill children is as important as the actual height of the fever.  In fact, “febrile seizures”--seizures due to rapid rise in body temperature that typically occur in children between the ages of 6 months and 3 years--appear to be related primarily to the fast rise of temperature.  About 4% of children under the age of 5 suffer a febrile seizure; usually no specific treatment (other than fever control) is required for these children (2).  The symptoms accompanying fever--whether as dramatic as a seizure or as nonspecific as flushing--give physicians clues to the source of the illness and the need and urgency for specific treatment.


What Types of Illnesses Cause Fever, and What Are Their Specific Symptoms?

          The most common source of fever in otherwise healthy children is a viral infection (2).  Viruses can cause croup, bronchiolitis (caused by respiratory syncitial virus or “RSV”) and other “URIs,” or upper respiratory infections, sore throat, nasal congestion or runny nose, cough, and muscle aches (4).  Other viruses cause gastrointestinal illnesses, marked by fever, nausea with or without vomiting, diarrhea, abdominal pain, and malaise.  Chicken pox is caused by the varicella virus, and in addition to typical skin lesions, may occasionally cause pneumonia in children.  Normally, such viral illnesses resolve on their own, over time (they may last as long as a week or two), with what physicians call “supportive care.”  Supportive care includes rest, lots of noncaffeinated fluids to drink, and over-the-counter medications such as cough syrup, decongestants, or acetaminophen.  Viral infections by definition do not improve with antibiotics, and in fact children with viral illness who are treated with antibiotics may end up feeling worse than they did before therapy.

          There are, of course, more serious viral infections.  Influenza is caused by a virus and can be a significant source of illness and even death, especially in the very young or chronically ill child.  Other important viruses that can cause fever in children include mononucleosis (which infects the lymph glands and spleen), hepatitis (liver), viral meningitis (fluid around the brain and spinal cord), and viral encephalitis (brain).  Although fever is nearly always present with one of these serious illnesses, other symptoms typically cause more concern and prompt consultation with a physician.  Viral illnesses also make children who have asthma more likely to have wheezing and breathing difficulty.

          A low-grade fever (less than 101 degrees Fahrenheit) may be associated with teething.  This probably results from inflammation of the gums as the teeth erupt, and not from an actual infection.  Teething fever resolves with acetaminophen and the child can be made more comfortable with cold liquids or popsicles. Infants may develop low-grade fevers from overdressing, sometimes called “overbundling.” The hypothalamus of a newborn is not as efficient as that of older children, so they sometimes do not regulate their body temperature effectively.  Parents should avoid overbundling, but should also not keep infants uncovered to the extent that the child shivers.

          Bacterial infections can occur in most organs and tissues in the body and are usually more serious than viral illnesses, even though most are easily treatable with antibiotics.  Fever is a typical feature of bacterial infections.  Fever associated with a bacterial infection of the central nervous system (brain and spinal cord) such as meningitis is typically accompanied by headache, stiff neck, and changes in behavior such as lethargy or confusion.  These symptoms should prompt urgent consultation with a physician.  In children, the middle ear is particularly prone to infection by both bacteria and viruses (5).  This is called “otitis media.”  Very young children may not be able to express the symptoms of a painful ear, but parents may notice a child--particularly one that has recently had a cold--pulling or tugging at one of his ears.  The skin, which is the largest organ of the body, can be infected by bacteria.  Usually there is a clear point of bacterial entry, such as a cut or scrape. Skin infections are characterized by fever accompanied by pain, redness, swelling, and warmth.  Sometimes pus drains from the area.  Antibiotics are used to treat such illnesses, which are called “cellulitis” (6). 

          The respiratory and gastrointestinal tracts are common locations for bacterial infections that cause fever.  Bronchitis and pneumonia cause cough and difficulty breathing in addition to fever, while gastrointestinal infections are associated with fever, abdominal pain, loss of appetite, vomiting, and/or diarrhea.  Urinary tract infections may cause fever, flank pain, nausea and vomiting, and burning and frequent urination.  The bottom line about bacterial infections is that, although fever is often part of the general illness, there are specific symptoms that can direct a caregiver to a specific cause and thence to specific antibacterial therapy.

          Another common cause of fever in children is immunizations.  Fever is common within a few hours of administration of the diphtheria-tetanus-pertussis (DTP) vaccine, and it may persist (along with fussiness) for a couple of days.  Fever may also occur after the administration of vaccines containing live viruses, such as the measles-mumps-rubella (MMR) vaccine, although often not until 7-10 days after the shot.  Treatment with acetaminophen or ibuprofen is effective.  Overall immunization status is also important when a child is evaluated by a physician for fever; the physician will want to know if the child has received pneumococcal, H.flu, and hepatitis vaccines because if the child is not up-to-date on these immunizations, the likelihood of serious illness underlying a high fever or other manifestations of severe illness may be greater.  It is also important to note that sometimes a very serious bacterial infection in children will cause the body temperature to be lowerthan normal.


How Do I Treat Fever?

          Fever in children can be treated with acetaminophen or ibuprofen.  Aspirin is not recommended because of its association with a rare but potentially fatal liver disease called Reye’s syndrome in some children with viral illnesses.  Both acetaminophen and ibuprofen can also help reduce the aches, pains, and fussiness that often accompany fever.  The dosing of acetaminophen and ibuprofen for fever is based on your child’s age and weight.  Acetaminophen (Tylenol®, Panadol®, Feverall®, etc.) comes in syrups, chewable tablets, and pills for swallowing; it can be given every four hours as need.  Ibuprofen (Advil®, Motrin®, Nuprin®, etc.) also comes in a variety of formulations and can be given to children every six hours.  It may be beneficial to alternate or even combine acetaminophen and ibuprofen when children have especially high fevers or feel very ill with their fever. Children younger than two months of age with a fever should always be evaluated by a physician.

          General treatment measures that might reduce an elevated body temperature and make the patient feel better overall include rest, oral hydration (with Pedialyte®, Gatorade®, or other rehydration fluids), and over-the-counter medications for specific fever-related symptoms, such as decongestants, cough remedies, or anti-diarrhea medications.  A sponge bath may make the child feel better, but it is important to use lukewarm--not cold--water, so as not to cause shivering, which raises body temperature.  Alcohol sponge baths are not recommended, nor are ice packs or cold baths.

          If a child experiences a febrile seizure, try to lay the child on his or her side and protect the child from falling or from injury from any nearby objects.  Febrile seizures typically do not last more than a couple of minutes, but to the parent observing it, it may seem to last much longer.  If possible, grab a watch and time the duration of the seizure activity, during which the child will typically shake and not be responsive to your words or physical comforting.  Don’t put anything in the child’s mouth and don’t do anything to try to stop the seizure. Simply protect the child from falling or otherwise hurting himself or herself.  A child who has had a febrile seizure should be evaluated in an emergency department as soon as possible.

          Although fevers in their children make parents anxious, low-grade fevers in healthy children don’t necessarily require aggressive treatment.  The illness underlying a fever in a child is probably not serious if the child remains playful, is eating and drinking, is alert and normally interactive with parents, and feels better when the temperature comes down.

          Ill children--even those with mild viral sicknesses--often experience a decreased appetite.  The child should generally be allowed to eat what he or she wants, in small amounts, and forced feedings are not necessary.  More attention should be paid to providing ample liquids and encouragement for drinking.  Children with fever should generally be kept out of school and daycare settings.  Generally it is safe to return to such activities when the child’s temperature has been normal for 24 hours.


Is There a Downside to Treating a Fever?

          This is an intriguing question for which the answer is not entirely clear.  What is known is that the answer varies by type of illness.  Acetaminophen and aspirin do not prolong the duration of a URI in adults, although they do appear to prolong the duration of the contagious interval and may worsen nasal congestion.  In a small study, acetaminophen did not impact the overall condition of children with chicken pox, but it did prolong the time until scabbing over of lesions (chicken pox is considered contagious until all lesions are scabbed over). Another study seemed to indicate that patients with influenza A treated with antipyretics had longer courses of illness than those who were not treated, although it also appeared that it was sicker patients--with higher fevers--who took the acetaminophen, so it may be that those patients were destined to remain ill longer, anyway.  What has not been studied well is the balance between symptomatic relief--i.e., reduction of the fever itself--and duration of illness; that is, even if patients are ill a day or two longer, do they feel better sooner with the fever treatment?  The thinking behind this question is that, if fever is a natural response to infection, and if the higher metabolic rate associated with fever helps the body fight infection, should we try to suppress fever and interfere with that immune response?  The viruses that cause URIs, for example, seem to thrive at cool temperatures.  In summary, however, available data at the present time suggest that there is little if any significant downside to the use of antipyretic medications in patients with fever associated with acute illness(7).


What Might the Doctor Do?

          As noted, children under 2 months of age should be evaluated by a physician for any fever.  Older children should be evaluated by a physician for a temperature higher than 102.2 degrees Fahrenheit, or when fever is accompanied by one of the symptoms listed in What Should I Worry About?  When Should I Call My Doctor?  If you have any doubt as to whether your child’s fever, or general condition, is critical, call your doctor to see whether you should bring the child in for an exam. 

The physician’s first and primary goal in assessing and managing fever is to make certain that the child does not have a life-threatening illness (8).  The types of very serious infections that are typically marked by very high fever include meningitis, pneumonia, bacteria in the bloodstream (called bacteremia), and appendicitis or other intra-abdominal infection.  The physician will first take a history of the patient’s possible exposure to pyrogens.  Has the patient been in close proximity to another ill child or adult with a fever?  Is the child chronically ill (9)?  Has he recently received a vaccination?  Is he in school or daycare?

          Next, a thorough history of the fever itself will be sought.  How high has the temperature been?  Does it stay elevated despite the use of acetaminophen or ibuprofen?  How many days has the fever been present?   

The physician’s next focus is on the patient’s other, non-fever, symptoms.  Symptoms that prompt immediate concern and thorough evaluation include new rashes, headache, stiff neck, persistent vomiting and/or diarrhea, and coughing or wheezing that makes breathing difficult.  What was the time course of these symptoms?  Did their appearance precede or follow the development of fever?  Are these symptoms getting worse?  Are there sweats associated with the fever, and do these occur throughout the day or only at night? The answers to these questions help guide the physician’s thinking; if the fever is high (>101.6 degrees Fahrenheit), generalized symptoms (aches, pains, malaise, fatigue) are not prominent, and the specific complaints are limited to the throat, chest, or abdomen, then bacterial infection is relatively more likely and antibiotics may be needed.  If the fever is lower (100.4-101.5 degrees Fahrenheit), systemic complaints are more prominent, and specific complaints are less apparent, then a viral illness is relatively more likely and antibiotics are not expected to be helpful. 

          A thorough physical examination will be performed to try to find the source of the fever.  If after these questions and examination the cause of the fever has not been definitely identified, then any of a wide variety of tests may be conducted.  These may include blood tests to determine the intensity of the body’s response to infection; culture samples of the throat, sputum, urine, or mucous and fluids from other sources; x-rays, including such tests as CAT scans; urine tests; and lumbar puncture (“spinal tap”) (FIGURE 4).  These tests not only confirm the presence of absence of infection but may also assist the physician in choosing a specific therapy beyond treatment of fever.  Such therapy may include antibiotics, but it is important to remember that the majority of fever-associated illnesses in children are caused by viruses, for which antibiotic therapy is not helpful.  Infants less than two months of age with fever are frequently kept in the hospital for ongoing observation and intravenous (into a vein) antibiotics.  Young children, from 2 months-2 years of age, may be sent home pending the results of various culture tests for bacterial infections, but often only after an intramuscular (into the muscle of the thigh or buttock) injection of a strong antibiotic, the effects of which last 24 hours or more; children so treated will ordinarily be brought back to the doctor’s office or emergency department for re-evaluation (and possibly another injection) the next day, until a final diagnosis is determined (8). 

How Do I Prevent Fever?

          Illnesses associated with fever are common in children between 2 months of age and middle-school age.  The vast majority of these illnesses are not serious, and children are back to normal within a few days. To some extent, illnesses that cause fever can be avoided by good parenting: encouragement of hand-washing (by both the children and the adults who care for them), keeping kids with fever out of school and daycare, and keeping immunizations up to date.  



1.  Carson SM: Alternating acetaminophen and ibuprofen in the febrile child: examination of the evidence regarding efficacy and safety. Pediatr Nurs 2003;29:379-82.

2.  Ishimine P: The evolving approach to the young child who has fever and no obvious source.  Emerg Med Clin N Am 2007;25(4):1087-1115.

3.  Ishimine P: Fever without source in children 0 to 36 months of age.  Pediatr Clin N Am 2006;53(2):167-94.

4.  Shah S: Pediatric respiratory infections.  Emerg Med Clin N Am 2007;25(4):961-79.

5.  Powers JH: Diagnosis and treatment of acute otitis media: Evaluating the evidence.  Infect Dis Clin N Am2007;21(2):409-26.

6.  Lopez FA: Skin and soft tissue infections.  Infect Dis Clin N Am  2006;20(4):759-72.

7.  Hudgings L, Safranek S: Do antipyretics prolong febrile illness?  J Fam Pract 2005;53:57-61.

8.  American College of Emergency Physicians Clinical Policies Subcommittee on Pediatric Emergency Medicine: Clinical policy for children younger than three years presenting to the emergency department with fever. Ann Emerg Med 2003;42:530-45.