Medical Author : John P. Cunha, DO, FACOEP
Medical Editor : Melissa Conrad Stöppler, MD
Aches, pain, fever facts
- Although a fever could be considered any body temperature above the normal 98.6 F (37 C), medically, a person is not considered to have a significant fever until the temperature is above 100.4 F (38.0 C).
- Most fever is beneficial, causes no problems, and helps the body fight off infections. The main reason for treating a fever is to increase comfort.
- Fever is the result of an immune response by your body to a foreign invader. These foreign invaders include viruses, bacteria, fungi, drugs or other toxins.
- Children under 3 months of age with a temperature of 100.4 F (38.0 C) or greater should be seen by a health care professional. They may be quite ill and not show any signs or symptoms besides a fever. Infants less than 6 weeks of age should be seen immediately by their doctor.
- Acetaminophen (Tylenol and others) and ibuprofen (Advil, Motrin) can be used to treat a fever. Aspirin should not be used in children or adolescents to control fever.
- The prognosis for a fever depends on the cause. Most cases of fever are self-limited and resolve with symptomatic treatment.
- A person who is taking immunosuppressant drugs or who has a history of or diagnosis of cancer, AIDS, or other serious illness, such as heart disease or diabetes, should seek medical care if a fever develops.
What is a fever?
Fever refers to an elevation in body temperature. Technically, any body temperature above the normal oral measurement of 98.6 F (37 C) or the normal rectal temperature of 99 F (37.2 C) is considered to be 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). 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 defenses against bacteria and viruses which cannot live at a higher temperature. For that reason, low fevers should normally go untreated, unless accompanied by troubling symptoms.
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, fatigue, joint pains or aches, chills, nausea, etc.
Fevers of 104 F (40 C) or higher demand immediate home treatment and prompt medical attention, as they can result in delirium and convulsions, particularly in infants and children.
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.
What causes a fever?
Fever is the result of an immune response by your body to a foreign invader. These foreign invaders include viruses, bacteria, fungi, drugs, or other toxins.
These foreign invaders are considered fever-producing substances (called pyrogens), which trigger the body's immune response. Pyrogens tell the hypothalamus to increase the temperature set point in order to help the body fight off the infection.
Fever is a common symptom of most infections. In children, immunizations or teething in may cause low-grade fever.Autoimmune disorders, medication reactions, seizures, or cancer may also cause fevers.
What are the signs and symptoms of a fever?
A fever can cause you 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, chills
- Aching muscles and joints
- Intermittent sweats
- Rapid heart rate and/or palpitations
- Skin flushing
- Feeling faint, dizzy, or lightheaded
- With very high temperature (> 104 F/40 C), convulsions, hallucination, or confusion is possible. Seek medical attention.
How is a fever diagnosed?
Along with having the generalized symptoms of a fever, taking your 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.
How should I 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 your child's armpit.
- Leave in place about one minute or until you hear a beep to check a digital reading.
Measuring fever by eardrum temperature
Tympanic (ear) thermometers must be placed correctly in your 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 you hear 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 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 your 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 your hand cupped around your child's bottom, and keep your fingers on the thermometer to avoid it accidently sliding further into the rectum. Keep it there for about one minute, until you hear 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.
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 your doctor.
The following 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 your physician.
- Ibuprofen (Motrin/Advil) can also be used to break a fever in patients over 6 months of age. Discuss the best dose with your doctor. For adults, 400 mg-600 mg (two to three 200 mg tablets) can be used every six 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 which causes prolonged vomiting, confusion, and even coma and liver failure.
Learn more about: Tylenol
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 are a home remedy that may help bring down a fever. Never immerse someone 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.
When should I seek medical care for a fever?
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.
Otherwise, observe the person with the fever. If they appear sick or have symptoms that would suggest a major illness, such as meningitis (headache, stiff neck, confusion, problems staying awake), urinary tract infection (shaking chills, burning with urination), pneumonia (shortness of breath, cough), or any other signs of a serious illness, contact your health care professional.
Other symptoms that may be indicative of a severe illness include repeated vomiting, severe diarrhea, or skin rashes (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, caused by a virus. 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 your child's doctor.
On the other hand, if the fever accompanies a simple cold or virus, you can treat the fever as described above and be assured that the fever is only a symptom of the illness. This is not to say that you should ignore a fever. If there are other associated symptoms that are bothersome, you should contact your 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 your child's doctor.
A low percentage of all children 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 episode. Febrile seizures, while frightening to the parents, are not associated with long-term nervous-system side effects. Children used to be prescribed phenobarbital 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 always recommended.
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 the fever. 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 depends on the cause. Most cases of fever are self-limited and resolve with symptomatic treatment. 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.
Can fevers be prevented?
Fever is preventable only to the extent that the specific cause of the fever can be prevented. Most fevers are caused by infection. Avoiding sources the infection and maintaining good hygiene practices are your 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 you and your child's immunizations are up to date.
Medically reviewed by Martin E Zipser, MD; American board of Surgery
Baumann, R. "Technical Report: Treatment of the Child With Simple Febrile Seizures." Pediatrics 103.6 June 1999: e86. <http://aappolicy.aappublications.org/cgi/content/full/pediatrics;103/6/e86>.
Davis, Bets. "Body Temperature." WebMD. Feb. 20, 2009. <http://www.webmd.com/a-to-z-guides/body-temperature>.
Davis, Charles P. "Fever in Adults." eMedicineHealth. Apr. 20, 2012. <http://www.emedicinehealth.com/fever_in_adults/article_em.htm>.
"How to Take a Child's Temperature." Healthy Children. June 15, 2010. <http://www.aap.org/publiced/BR_Fever.htm>.
Webster's New World Medical Dictionary, Third Edition
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