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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:
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.
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:
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