- 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 to treat a fever is to increase comfort.
- Fever is the result of an immune response by your body to a foreign invader. Foreign invaders include virus, 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 younger than 6 weeks of age should be seen immediately by their doctor.
- Acetaminophen (Tylenol and others) ibuprofen (Advil and 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 treatment of symptoms.
- 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?
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 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 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.
What Causes 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 signal the hypothalamus in the brain to increase the body temperature set point in order to help the body fight off the infection.
Fever is a common symptom of most infections such a colds and gastroenteritis (also referred to as stomach flu), and thus a risk factor for fever is exposure to infectious agents. Typical infections that may cause a fever include those of the ear, throat, lung, bladder, and kidney. In children, immunizations (such as vaccine shots) or teething may cause short-term low-grade fever. Autoimmune disorders (including rheumatoid arthritis, lupus, and inflammatory bowel disease), medication side effects, seizures, blood clots, hormone disorders, cancers and illicit drug use may also cause fevers.
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 soars
- Loss of apetite
- Fussiness (in children and toddlers)
- Also important to note in children are symptoms that can accompany an infection, including cough, ear ache, vomiting and diarrhea
- With very high temperatures (>104 F/40 C), convulsions, hallucination or confusion is possible. Always seek medical attention for a high fever or if these symptoms occur.
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.
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 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.
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