What is a fever?
The definition of fever is an elevation in body temperature or a high body temperature. Technically, any body temperature above the normal oral measurement of 98.6 degrees Fahrenheit (37 Celsius) or the normal rectal temperature of 99 F (37.2 C) is considered elevated. However, these are averages, and one's normal body temperature may actually be 1 F (0.6 C) or more above or below the average of 98.6 F. Body temperature can also vary up to 1 F (0.6 C) throughout the day.
- Fever is not considered medically significant until body temperature is above 100.4 F (38 C), which is the temperature considered to be a fever by medical professionals. Anything above normal but below 100.4 F (38 C) is considered a low-grade fever. Fever serves as one of the body's natural infection-fighting defenses against bacteria and viruses that cannot live at a higher temperatures. For that reason, low-grade fevers should normally go untreated, unless accompanied by troubling symptoms or signs.
- Also, the body's defense mechanisms seem to work more efficiently at a higher temperature. Fever is just one part of an illness, many times no more important than the presence of other symptoms such as cough, sore throat, sinus congestion, fatigue, joint pains or aches, chills, nausea, etc.
- Fevers of 104 F (40 C) or higher may be dangerous and demand immediate home treatment and prompt medical attention, as they can result in delirium and convulsions, particularly in infants, children, and the elderly.
- Fever should not be confused with hyperthermia, which is a defect in your body's response to heat (thermoregulation), which can also raise the body temperature. This is usually caused by external sources such as being in a hot environment. Heat exhaustion and heat stroke are forms of hyperthermia. Other causes of hyperthermia can include side effects of certain medications or medical conditions.
- Fever should also not be confused with hot flashes or night sweats due to hormonal changes during perimenopause (the time period around menopause). Hot flashes and night sweats cause a sudden and intense feeling of heat, and may be accompanied by flushing (skin redness and tingly feeling) and sweating, but are not the same thing as a fever.
Which illness is known as a viral upper respiratory tract infection?
What are the signs and symptoms of a fever?
A fever can cause a person to feel very uncomfortable. Signs and symptoms of a fever include the following:
- Temperature greater than 100.4 F (38 C) in adults and children
- Shivering, shaking, and chills
- Aching muscles and joints or other body aches
- Intermittent sweats or excessive sweating
- Rapid heart rate and/or palpitations
- Skin flushing or hot skin
- Feeling faint, dizzy, or lightheaded
- Eye pain or sore eyes
- Loss of appetite
- Fussiness (in children and toddlers)
- Also important to note in children are symptoms that can accompany an infection, including sore throat, cough, earache, vomiting, and diarrhea
- With very high temperatures (>104 F/40 C), convulsions, hallucinations, or confusion is possible. Always seek medical attention for a high fever or if these symptoms occur.
How to Prevent the Common Cold
How do health care professionals diagnose a fever?
- Along with having generalized symptoms of a fever, taking one's temperature with a thermometer can confirm the diagnosis of a fever. A temperature greater than 100.4 F in adults or children is considered a fever.
- Different tests may be done by a doctor, such a blood and imaging tests, to determine the cause of a fever and if the cause of the fever needs to be treated.
How should someone take a temperature for fever?
Digital thermometers can be used to measure rectal, oral, or axillary (under the armpit) temperatures. The American Academy of Pediatrics does not recommend use of mercury thermometers (glass), and they encourage parents to remove mercury thermometers from their households to prevent accidental exposure to this toxin.
Measuring an axillary (under the armpit) temperature for fever
Axillary temperatures are not as accurate as rectal or oral measurements, and these generally measure 1 degree lower than a simultaneously obtained oral temperature.
- Place the tip of the digital thermometer in a child's armpit.
- Leave the thermometer in place about one minute or until one hears a beep to check a digital reading.
Measuring fever by eardrum temperature
Tympanic (ear) thermometers must be placed correctly in a child's ear to be accurate. Too much earwax can cause the reading to be incorrect.
Eardrum temperature measurements are not accurate in small children and should not be used in children under 3 years (36 months) of age. This is especially true in infants below 3 months of age when obtaining an accurate temperature is very important.
Measuring fever by oral temperature
People 4 years old and older can have their temperature taken with a digital thermometer under the tongue with their mouth closed.
- Clean the thermometer with soapy water or rubbing alcohol and rinse.
- Turn the thermometer on and place the tip of the thermometer as far back under the tongue as possible.
- The mouth should remain closed, as an open mouth can cause readings to be inaccurate.
- The thermometer should remain in place for about one minute or until one hears the beep. Check the digital reading.
Avoid hot or cold drinks within 15 minutes of oral temperature measurement to ensure correct readings.
Measuring fever by rectal temperature
The American Academy of Pediatrics recommends rectal temperature measurements for children and toddlers under 3 years of age, as this gives the most accurate reading of core temperature.
- Clean the thermometer with soapy water or rubbing alcohol and rinse with cool water.
- Use a small amount of lubricant, such as petroleum jelly, on the end.
- Place the child or baby prone (belly-side down) on a firm surface, or place a child face up and bend his legs to his chest.
- After separating the buttocks, insert the thermometer approximately ½ to 1 inch into the rectum. Do not insert it too far.
- Hold the thermometer in place, loosely keeping one's hand cupped around the child's bottom, and keep one's fingers on the thermometer to avoid it accidently sliding further into the rectum. Keep it there for about one minute, until one hears the beep.
- Remove the thermometer, and check the digital reading.
- Label the rectal thermometer so it's not accidentally used in the mouth.
A rectal temperature will read approximately 1 degree higher than a simultaneously obtained oral temperature.
Subscribe to MedicineNet's General Health Newsletter
What is the treatment for a fever?
Generally, if the fever does not cause discomfort, the fever itself need not be treated. It is not necessary to awaken an adult or child to treat a fever unless instructed to do so by a doctor.
The following over-the-counter fever-reducing medications may be used at home:
- Acetaminophen (Tylenol and others) can be used to lower a fever. The recommended pediatric dose can be suggested by the child's pediatrician. Adults without liver disease or other health problems can take 1,000 mg (two "extra-strength" tablets) every six hours or as directed by a physician. The makers of Tylenol state the maximum recommended dose of acetaminophen per day is 3,000 mg, or six extra-strength tablets per 24 hours, unless directed by a doctor. Regular-strength Tylenol tablets are 325 mg; the recommended dosage for these is two tablets every four to six hours, not to exceed 10 tablets per 24 hours. If your fever is accompanied by vomiting and you are unable to keep oral medications down, ask a pharmacist for acetaminophen suppositories, which are available without a prescription.
- Ibuprofen (Motrin, Advil) can also be used to break a fever in patients over 6 months of age. Discuss the best dose with a doctor. For adults, generally 400 mg to 600 mg (two to three 200 mg tablets) can be used every six hours as fever reducers.
- Naproxen (Aleve) is another nonsteroidal anti-inflammatory drug (NSAID) that can temporarily reduce fever. The adult dose is two tablets every 12 hours.
- Aspirin should not be used for fever in children or adolescents. Aspirin use in children and adolescents during a viral illness (especially chickenpox and influenza, or flu) has been associated with Reye's syndrome. Reye's syndrome is a dangerous illness that causes prolonged vomiting, confusion, and even coma and liver failure.
Health Solutions From Our Sponsors
What are home remedies for a fever?
- An individual with a fever should be kept comfortable and not overdressed. Overdressing can cause the temperature to rise further. Tepid water (85 F [30 C]) baths or sponge baths are a home remedy that may help bring down a fever. Never immerse a person with a fever in ice water. This is a common misconception. Never sponge a child or an adult with alcohol; the alcohol fumes may be inhaled, causing many problems.
- Other home remedies for fever include staying hydrated. Drink plenty of water and fluids, and avoid alcohol or caffeinated beverages, which can contribute to dehydration. Popsicles can also be cooling and provide fluids while also soothing a sore throat if that is present.
- A fan to circulate air or an open window may be helpful, as well as applying a cool damp washcloth to the forehead. If you are caring for a child, make sure the child does not feel too cold.
When should you worry about fever?
- A fever over 104 F/40 C in children and adults is considered dangerous. Seek medical attention immediately.
- Any child below 3 months of age who has a temperature of 100.4 F (38 C) or greater should be seen by a physician. If a child or adult has a history or diagnosis of cancer, AIDS, or other serious illness, such as heart disease, diabetes, or is taking immunosuppressant drugs, medical care should be sought for a fever.
- Children with a fever who have signs and symptoms such as rash, sore throat, ear pain, stiff neck, drowsiness, fussiness, or headache should see a doctor. In addition, if a fever lasts more than one day in a child or toddler 2 years of age or under, or last more than three days in a child over age 2, seek medical care.
- Otherwise, observe the person with the fever. If he or she appears sick or has symptoms that would suggest a major illness, such as meningitis (headache, stiff neck, confusion, problems staying awake), urinary tract infection (shaking chills, back pain, burning with urination), pneumonia (shortness of breath, cough), or any other signs of a serious illness, contact a health care professional.
- Other symptoms that may be indicative of a severe illness include repeated vomiting, severe diarrhea, or skin rashes (that could be a sign of dengue fever, Rocky Mountain spotted fever, scarlet fever, rheumatic fever, strep throat, or chickenpox).
- Fever blisters (herpangina) are small blisters that turn into ulcers, usually on the lips, mouth, or tongue; a virus causes fever blisters. When a child contracts this virus for the first time, the symptoms and the fever blisters can be quite severe. If the child is not eating or drinking, contact the child's pediatrician.
- Women who are pregnant should contact a doctor for a fever over 101 F (38 C). A fever during pregnancy that is accompanied by a rash and joint pain could be a sign of an infection that could affect the baby. Some infections, such as cytomegalovirus (CMV), can cause congenital deafness and other problems in the baby. If a pregnant woman contracts the Zika virus (also called Zika fever), it may cause a birth defect called microcephaly (small head).
- On the other hand, if the fever accompanies a simple cold or virus, one can treat the fever as described above and be assured the fever is only a symptom of the illness. This is not to say one should ignore a fever. If there are other associated symptoms that are bothersome, contact a doctor.
- Some vaccines given in childhood can cause a low-grade fever within a day or two of getting the injection. This fever is usually self-limited and short-lived. If the reaction seems severe or the skin at the injection site is red, hot, and painful, contact the child's doctor.
- A low percentage of all children and toddlers between 18 months to 3 years of age will have a seizure (convulsion) with a high fever. Of those with a history of febrile seizure, some will have another seizure associated with another febrile (fever) episode. Febrile seizures, while frightening to the parents, are not associated with long-term nervous-system complications. Children used to be prescribed the antiseizure drug phenobarbital (Solfoton, Luminal) following a febrile seizure as a preventive measure (prophylaxis). This has not been shown to be beneficial and possibly may be harmful, so it is not recommended.
- Recurrent fever in children (three or more episodes of fever in a six-month period, with no apparent causative illness) can be a symptom of a few different illnesses, such as PFAPA (periodic fever, aphthous ulcers, pharyngitis, and adenopathy) syndrome, cyclic neutropenia, Epstein-Barr virus (EBV) infection, and others. See your child's pediatrician if fevers are recurrent.
- Recurrent, persistent, or chronic fever in adults may accompany immune-deficient fever of unknown origin (FUO), also known as neutropenic FUO, and HIV-associated FUO, as well as many other infectious conditions. Adults should see their doctors if they develop recurrent fever.
What kind of doctors treat a fever?
Any kind of doctor is able to treat a fever, but most likely when you have a fever you will see your family medicine specialist (also called a general practitioner) or internist, and your child will see a pediatrician. You may see an emergency medicine specialist in an emergency department.
If fever is due to a specific underlying or recurrent medical condition, you may see a specialist for that particular condition. For example, if a person has cancer and a fever, an oncologist may be consulted. A pregnant woman with a fever may see her obstetrician. Newborns with fever may see neonatal specialists. Patients with HIV/AIDS and fever may consult an infectious disease specialist.
What are complications of a fever?
While having a fever is generally very uncomfortable, a fever itself does not usually cause severe complications.
High fever (>103 F/40 C) or prolonged bouts of fever can lead to
It is important to seek treatment for the underlying cause of a fever in the situations described above. Many of the infections that can cause fever can lead to severe complications if untreated.
What is the prognosis for a fever?
The prognosis for a fever and how long it lasts depends on the cause. Most cases of fever are self-limited and resolve with symptomatic treatment. For example, a fever associated with a common cold usually only lasts two to three days. If fever is caused by influenza, most flu symptoms including fever go away in about a week. Depending on the cause, antibiotics or other appropriate medications may be used.
Fevers associated with severe infections, or in patients whose immune system is compromised (such as those with cancer, elderly people, newborn infants, patients with HIV/AIDS, or people with autoimmune disorders), can be life-threatening.
3 Possible ways to prevent a fever
Prevention of fever is possible only to the extent that the specific cause of the fever can be prevented. Most fevers are caused by infection. Avoiding sources of infection and maintaining good hygiene practices are the best way to prevent a fever.
Some ways to prevent the spread of infection include the following:
- Proper hygiene: Wash hands frequently.
- Avoid contact with sick people.
- Make sure immunizations are up to date.
Where can people find more information about fevers?
American Academy of Pediatrics
141 Northwest Point Boulevard
Elk Grove Village, IL 60007-1098
Medically Reviewed on 7/1/2019
American Academy of Pediatrics. "Treating a Fever Without Medicine." Aug. 20, 2015. <https://www.healthychildren.org/English/health-issues/conditions/fever/Pages/Treating-a-Fever-Without-Medicine.aspx>.
Pappas, Diane E. "Patient Information: The Common Cold in Children (Beyond the Basics)."
UpToDate.com. Aug. 4, 2015. <http://www.uptodate.com/contents/the-common-cold-in-children-beyond-the-basics>.
Roth, Alan R., and Gina M. Basello. "Approach to the Adult Patient with Fever of Unknown Origin." American Family Physician 68.11 Dec. 1, 2003: 2223-2229. <http://www.aafp.org/afp/2003/1201/p2223.html>.
Sadovsky, Richard. "Recurrent Fevers in Children: Differential Diagnosis." American Family Physician 67.4 Feb. 15, 2003. <http://www.aafp.org/afp/2003/0215/p863.html>.
United States. Centers for Disease Control and Prevention. "Question and Answers: Zika virus infection (Zika) and pregnancy." Aug. 9, 2016. <http://www.cdc.gov/zika/pregnancy/question-answers.html>.
Ward, Mark A. "Patient Information: Fever in Children (Beyond the Basics)."
UpToDate.com. Aug. 31, 2015. <http://www.uptodate.com/contents/fever-in-children-beyond-the-basics>.
Webster's New World Medical Dictionary, Third Edition