Fever is an increase in body temperature that can be a symptom of an underlying illness in a child. It is not an illness in itself, except in the case of heat stroke. Fever is the body’s response to disease and is designed to kill germs outright and stimulate the immune system to fight bacteria and viruses.

Fever may develop at various speeds and may reach heights ranging from 100.4 degrees to 104 degrees Fahrenheit (38 degrees and 40 degrees Celsius) or higher. Fevers are either acute (short duration with a definite endpoint) or chronic (recurring repeatedly over time). Because fever is a natural and healthy response to illness, it typically does not need to be treated except to relieve a child’s discomfort. A thermometer can be used to detect a fever. These instruments come in many varieties.

Children who have a fever are likely to experience associated symptoms such as perspiration, flushed appearance, lethargy or fatigue, loss of appetite (anorexia), chills, muscle aches and headaches. A febrile seizure may occur in children with very high fevers and is marked by temporary loss of consciousness and convulsions. Very high fevers also can cause hallucinations, confusion and irritability.

Viral and bacterial infections are the source of most acute fevers, while a number of medical conditions – including juvenile rheumatoid arthritis, chronic or relapsing infections and cancer – can cause chronic fevers. In rare cases, no cause can be determined for a persistent fever. Such conditions are described as “fevers of unknown origin.”

Fever itself is generally not an illness and usually does not require treatment. Nonetheless, parents often desire to reduce a fever because of the discomfort it may cause to a child. Non-aspirin fever reducers can be used to reduce a fever and lessen associated symptoms such as achiness and chills. Children also should get plenty of rest and drink plenty of fluids to avoid dehydration. Other techniques that may be useful in keeping children comfortable include dressing the child in light clothing and cooling the child with lukewarm sponge baths.

Parents are urged to consult a physician when a child under 6 months of age has a fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or a child older than 6 months has a fever of 101 degrees Fahrenheit (38.3 degrees Celsius) or higher. Any fever in an infant who is 3 months old or younger always should be reported to a healthcare professional, preferably a pediatrician, because it often indicates a potentially serious infection. Parents should also take their child to a physician if the fever is accompanied by various other symptoms (e.g., rash, seizure).

Though fevers cannot always be prevented, frequent handwashing can help prevent children from picking up germs and infecting themselves by touching their mouths, nose or eyes.

Fever is an increase in body temperature of at least 1 degree Fahrenheit that is symptomatic of an underlying illness in a child. Fever can be as low as 99 degrees Fahrenheit (37.2 degrees Celsius) but is more likely to be at least 100 degrees Fahrenheit (37.8 Celsius) in children.

Normally, the body maintains an internal temperature somewhere between 97 degrees and 100.5 degrees Fahrenheit (36.1 degrees and 38.1 degrees Celsius), with the average being 98.6 degrees Fahrenheit (37 degrees Celsius). The exact temperature varies from child to child, and a child’s body temperature also fluctuates throughout the day. Typically, this variation is only 1 degree or so, and body temperature tends to be lower in the morning and higher in the evening. 

Fever is part of the body’s response to disease. The portion of the center of the brain called the hypothalamus increases internal body temperature to kill germs and stimulate the immune system to fight bacteria and viruses. Various conditions can cause a fever to develop. In most cases, these sicknesses are minor, such as a mild bacterial or viral infection. However, sometimes fever is an indicator of a more serious disease, especially when the fever occurs in very young children.

Fevers are either acute (short duration with a definite endpoint) or chronic (recurring repeatedly over time). Because fever is a natural and healthy response to illness, it typically does not need to be treated except to relieve a child’s discomfort. However, fever can become dangerous if a child’s body temperature becomes too high.

A thermometer can be used to detect a fever. These instruments come in many varieties, including digital thermometers, electronic ear thermometers, forehead thermometers and pacifier thermometers. Digital thermometers provide the most quick and accurate temperature readings. Forehead and pacifier thermometers are less accurate and are usually not recommended.

In the past, mercury thermometers were the standard instrument used to take a child’s temperature. However, organizations such as the American Academy of Pediatrics no longer approve of the use of mercury thermometers because they can potentially expose a child to the toxic effects of mercury. Mercury thermometers are no longer commercially available.

Temperatures are most often taken with oral, rectal or axillary (under the arm) thermometers. In most cases, temperatures should be taken rectally in children younger than age 3 and orally thereafter. When taking a temperature rectally, the thermometer should be coated in petroleum jelly and inserted a half-inch (1.27 centimeters) into the rectum and held there until temperature is taken, usually about one minute.

The following standards are used to determine when a child has a fever:

Fever may develop at various speeds and may reach heights ranging from 100.4 degrees to 104 degrees Fahrenheit (38 degrees and 40 degrees Celsius) or higher. The speed and height of a temperature is not necessarily indicative of the seriousness of the underlying disease. The fever may fluctuate or remain mostly steady throughout a child’s illness.

Children who have a fever are likely to experience several associated symptoms. Typically, they will perspire, causing the skin to become hot and moist as body temperature increases. They also may have a flushed appearance, and may become lethargic or fatigued. Loss of appetite (anorexia), chills (resulting from the body’s attempt to generate extra heat), muscle aches and headaches often accompany fever.

A febrile seizure may occur in children whose fever rises very quickly and reaches heights of around 105 degrees Fahrenheit (40.6 degrees Celsius) or more. This type of seizure most often affects children between the ages of 6 months and 3 years. Symptoms include brief loss of consciousness and convulsions. However, the effects of a febrile seizure are usually not permanent.

Fevers between 103 degrees and 106 degrees Fahrenheit (39.4 degrees and 41.1 degrees Celsius) may trigger hallucinations, confusion, irritability and convulsions.

Viral and bacterial infections are the source of most acute (short-duration) fevers. Examples of viral infections include colds and influenza or chickenpox. Bacterial infections include strep throat, meningitis, pneumonia, Rocky Mountain spotted fever (spread by wood tick bite), sepsis (infection of the blood) and urinary tract infections. Other sources of acute fever include:

• Heat stroke. An abnormal rise in body temperature that can cause a high and potentially fatal fever. Heat stroke is one form of fever that qualifies as an illness in and of itself. It occurs in situations where the body becomes overheated. Examples include a child who stays outside too long on a hot day or an infant left in a hot car.
  
  
• Ear infections (otitis media). Common in children, ear infections may cause a fever along with pain, difficulty hearing and sometimes diarrhea.
  
  
• Immunizations. Some children may develop a low-grade fever after they have a vaccination shot, such as diphtheria, tetanus and pertussis or pneumococcal vaccines.
  
  
• Medication use. The use of medications such as antibiotics and antihistamines sometimes can cause fever as a side effect.
  
  
• Overdressing an infant. Very young children may get fevers if they are dressed too warmly in a hot environment because they cannot properly adjust body temperature.
  
  
• Teething. A low-grade fever sometimes occurs when an infant is teething.
  
  
• Poisoning. Chemical pneumonia accompanied by fever can result from inhaling hydrocarbon chemicals found in substances such as gasoline or furniture oil.
  
  
• Temporal arteritis. This inflammation of an artery in the head can cause a fever.

Chronic fevers also are caused by a number of different conditions. For example, viral infections that occur in sequence (such as a series of colds) can cause recurrent fever. Chronic or relapsing infections (such as tuberculosis, malaria or typhoid) also can cause chronic fevers. Other sources of chronic fever include:

• Autoimmune diseases such as juvenile rheumatoid arthritis or lupus.
  
  
• Endocrine gland disorders such as hyperthyroidism (excessive secretion of thyroid hormone).
  
  
• Hereditary disorders such as Mediterranean fever (rare disorder that causes fever and pain in the abdomen, chest and joints).
  
  
• Cancers. Malignant tumors and forms of kidney cancer can cause recurring fevers.

In rare cases, no cause can be determined for a persistent fever. Such “fevers of unknown origin” tend to be at least 100.5 degrees Fahrenheit (38.1 degrees Celsius) and last for two to three weeks. In most cases, a physician eventually will find the source of the fever. In younger children, this tends to be viral or bacterial infections. In older children, an inflammation of connective tissue is often responsible.

In addition, recent findings indicate that using positron emission tomography (PET scan) with the radioactive tracer 18-fluoro-deoxy-glucose (18-FDG) can provide early diagnosis of causes of fevers of unknown origin (e.g., cancer) and eliminate the need for additional thorough and invasive diagnostic tests. A PET scan is a minimally invasive radionuclide imaging test that produces three-dimensional images of the living heart, brain, liver or other organs at work. The scan works by creating computer images of the chemical changes that take place inside tissue. These images can provide information on blood flow, oxygen consumption, blood sugar metabolism and concentrations of various compounds in selected organs.

Although the amount of radiation used in PET scans is so low that it poses no health risks to most patients, infants and young children may have a higher level of vulnerability to the radiation.

Fever itself is generally not an illness and usually does not require treatment. Some health experts believe that treating a fever prevents the body from using natural defenses to eradicate an illness. Nonetheless, parents often desire to reduce a fever because of the discomfort it may cause to a child. Non-aspirin fever reducers can be used to reduce a fever and lessen associated symptoms such as achiness and chills. Parents should never use aspirin to treat their child, as the use of this drug in children with bacterial and viral infections can lead to Reye syndrome, a rare condition that can damage the brain or liver.

Children also should get plenty of rest and drink plenty of fluids to avoid dehydration. Water and fruit juices are best for restoring loss of fluids. However, children should be allowed to drink whatever liquids they most enjoy as long as they do not contain caffeine. Sports drinks should not be given to young children because the added sugars may cause diarrhea.

A physician also may recommend an over-the-counter pediatric electrolyte rehydration solution that will keep a child’s mineral levels in balance. It is not a good idea to “starve” a fever by curbing a child’s intake of calories. Regular meals provide a child with the energy needed to fight off a fever.

Other techniques that may be useful to keep children comfortable include dressing the child in light clothing and cooling the child with lukewarm sponge baths. Water should not be too cool or it may cause the child to shiver, which may raise the fever even higher. Sponge baths may be a good option for children who have temperatures of 103 degrees Fahrenheit (39.4 degrees Celsius) for more than one hour. A child’s temperature should begin to fall within five or 10 minutes of beginning the sponge bath. Rubbing alcohol should not be used as a substitute for or in addition to lukewarm water. Rubbing alcohol may be absorbed into the skin or inhaled. This can result in a coma. 

Ultimately, the most important factor in eliminating a fever is to treat the underlying condition that has caused the increased body temperature. Many conditions that cause fever will pass on their own without treatment, including viral infections such as influenza and mononucleosis. In other cases – such as bacterial infections, including strep throat and pneumonia – antibiotics may be necessary.

Parents are urged to check their child’s temperature every four to eight hours and to call a physician if a child under 6 months of age has a fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or if a child older than 6 months has a fever of 101 degrees Fahrenheit (38.3 degrees Celsius) or higher. Prompt medical care is required for children under 2 who have a fever for more than 12 hours, or for children older than 2 whose fever persists for more than two days.

Fever in an infant who is 3 months old or younger should always be reported to a healthcare professional, preferably a pediatrician, as it often indicates a potentially serious infection.

Parents should notify a physician of their child’s fever if the child has a history of a disease that suppresses the immune system – such as diabetes, sickle cell anemia or cancer – or is taking corticosteroids. In addition, any child whose fever is accompanied by any of the following symptoms also should receive medical attention:

• Abdominal pain
• Blue lips, nails and tongue (cyanosis)
• Breathing difficulties
• Difficulty waking
• Drooling
• Inconsolable crying that lasts for hours
• Joint pain
• Lethargy
• Loss of mental alertness
• Marked drowsiness
• Stiff neck and pain when bending head forward
• Mental confusion
• Pain during urination
• Recent and spreading rash or purple spots on the skin
• Seizure
• Severe headache
• Severe throat swelling
• Swelling of the soft spot on the head (fontanel) in infants

Children with a fever who also experience stiff neck, inability to bend the head forward or heightened sensitivity to bright lights also should see a physician. These symptoms may indicate meningitis, a serious inflammation of the membrane covering the brain and spinal cord. Meningitis requires immediate emergency medical attention.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Parents and children may wish to ask their doctor or other healthcare professional the following questions about fever:

1. How do I know if my infant has a fever?
   
   
2. What signs indicate that my child’s fever requires medical attention?
   
   
3. What is the likely cause of my child’s fever?
   
   
4. What treatments do you recommend for my child’s underlying condition?
   
   
5. If my child is diagnosed with a “fever of unknown origin,” what happens next?
   
   
6. How should I use a thermometer to take my child’s temperature?
   
   
7. Do you need to know what method I used to take my child’s temperature?
   
   
8. Am I potentially delaying my child’s recovery by treating the fever?
   
   
9. Is it OK to treat my child with a fever-reducing medication? Are there any that I should avoid?
   
   
10. Should I give my child a pediatric electrolyte rehydration solution?
    
    
11. How can I help prevent future fevers in my child?