• Although a fever (pyrexia) could be considered any body temperature above the normal temperature of 98.6 degrees Fahrenheit (98.6 F or 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 viruses, bacteria, fungi, drugs, or other toxins.
  • Children under 3 months of age with a higher-than-normal 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) 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 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.

When to Call the Doctor for a Fever

Fever is a routine symptom in infants and children. It is a normal immune response to an infection to generate an elevated body temperature and make the body inhospitable. That doesn’t mean that the fever should be ignored, but if the child is otherwise doing well, treating the fever with over-the-counter (OTC) medicines such as acetaminophen (Tylenol and many others) or ibuprofen (Advil, Motrin, and many others) may be all that is needed.

 

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.

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What causes a fever?

  • Fever is the result of your immune system’s response 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 as colds, flu, 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 are some non-infectious causes of fevers.
  • Fever itself is not contagious; however, if the fever is caused by a viral or bacterial infection, the infection may be contagious.