Diseases & Conditions



Fever is a rise in body temperature in response to infection, injury, or inflammation (see Biology of Infectious Disease: Fever ).

Body temperatures vary, and temperature elevations up to 100.3° F (about 38° C) can be normal in healthy children. Therefore, minor temperature elevations that do not distress a child do not require medical attention. Temperatures of 100.4° F (about 38° C) and higher are considered abnormal and usually deserve attention, particularly in infants younger than 3 months.

Causes and Symptoms

Fever is usually the result of common infections, such as colds and gastroenteritis. These infections are usually viral and get better without treatment. Less commonly, fever develops because of infection in the ear, lung, bladder, or kidney; these are usually bacterial infections that require antibiotics. In infants on rare occasions, fever may be the only sign of a bloodstream infection (occult bacteremia (see Bacterial Infections: Bacteremia (Occult) ), which can lead to meningitis and overwhelming infection (sepsis), two life-threatening conditions. Children with these kinds of infection usually appear ill. Many conditions besides infection cause fever in children, but all are rare. Unlike fevers that occur with common infections, these fevers persist for more than a few days.

Fevers can occur after routine vaccinations and are not a reason to avoid recommended vaccines. Giving the infant acetaminophen Some Trade Names TYLENOL or ibuprofen Some Trade Names ADVIL MOTRIN NUPRIN at the time of vaccination and afterward minimizes the risk of getting a fever or lowers the fever itself.

Infants with fever are usually irritable and may not sleep or feed well. Older children lose their interest in play, although sometimes children with high fevers appear surprisingly well. The irritability and disinterest that fever usually causes worsen the higher the fever gets. Occasionally, a rapidly rising fever can cause seizures (febrile seizures), and quite rarely, a fever gets so high that children become lethargic and unresponsive.

Diagnosis and Treatment

Detecting fever is not a challenge, but determining its cause can be. If the fever is low grade (100.3° F [about 38° C] or below) and of short duration, no testing or treatment may be needed. In other cases, knowledge of the child's symptoms and a thorough examination help doctors find the cause. In general, any infant with a temperature of 100.4° F (about 38° C) or higher should be seen by a doctor, as should older children with higher or recurring fevers or complaints of pain.

In infants younger than 2 months of age who have a fever, doctors may order blood and urine tests and perform a spinal tap (lumbar puncture (see Diagnosis of Brain, Spinal Cord, and Nerve Disorders:Procedures ) to look for occult bacteremia, urinary tract infection, and meningitis. The reason for these tests is that in infants, the source of fever is difficult to determine. They are also at risk of serious infection compared with older children because of their immature immune system. Doctors may also order an x-ray if the infant's breathing is abnormal. For infants older than 2 months of age, testing may not be needed, but many doctors order blood and urine tests and perform a spinal tap if the source of the fever is not obvious and the child appears ill. For children 3 months of age and older, doctors rely more on the child's behavior and physical examination to determine which tests to order. Doctors may order blood and urine tests for children younger than 3 years old with high fevers if they cannot determine the source of fever after examining the child.

Most fevers do not require treatment except to make the child feel better and thus more willing to drink, avoiding dehydration. Acetaminophen Some Trade Names TYLENOL and ibuprofen Some Trade Names ADVIL MOTRIN NUPRIN are used. Aspirin Some Trade Names ECOTRIN ASPERGUM is not safe for lowering fever because it can interact with certain viral infections and cause a serious condition called Reye's syndrome (see What Is Reye's Syndrome? ). A warm (not cold) bath can sometimes make an older child feel better by reducing the fever. Rubbing the child down with alcohol or witch hazel is not recommended. Alcohol or witch hazel may have harmful fumes, come into contact with the eyes, or be accidentally ingested.

Additional treatment depends on the child's age and cause of the fever. Rarely, fevers persist and doctors are unable to determine the source even after extensive testing. This type of fever is called fever of unknown origin (see Biology of Infectious Disease: Fever ).

How to Take a Child's Temperature

A child's temperature can be taken from the rectum, the ear, the mouth, or the armpit. can be taken with a glass or digital thermometer. Thermometers containing mercury are no longer recommended because of the risk of breakage and exposure to mercury.

Rectal temperatures are most accurate; that is, they come closest to the child's true internal body temperature. To take a rectal temperature, a thermometer with a coat of petroleum jelly around the bulb should be gently inserted about ½ to 1 inch (about 1¼ to 2½ centimeters) into the child's rectum while the child is lying face down. The child should be kept from moving. The thermometer should be kept in place for 2 to 3 minutes before removing it and taking a reading.

Ear temperatures are taken with a digital device that measures infrared radiation from the eardrum. Ear thermometers are unreliable in infants younger than 3 months of age. To take an ear temperature, the person should form a seal around the opening of the ear with the thermometer probe and press the start button. A digital readout provides the temperature.

Oral temperatures are taken by placing a glass or digital thermometer under the child's tongue for 2 to 3 minutes. Oral temperatures provide reliable readings but are difficult to take in young children, who usually cannot keep their mouth gently closed around the thermometer to get an accurate reading.

Armpit temperatures are taken by placing a glass or digital thermometer in the child's armpit for 4 to 5 minutes. Armpit temperatures are least accurate because the armpit is cooler than the rectum, ear, or mouth.

Last full review/revision January 2007 by Elizabeth J. Palumbo, MD

Source: The Merck Manual Home Edition