First Aid & Emergencies

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Fever Facts

Although a fever -- also known as a high fever or a high temperature -- is not by itself an illness, it's usually a symptom of an underlying condition, most often an infection.

Fever is usually associated with physical discomfort, and most people feel better when a fever is treated. But depending on your age, physical condition, and the underlying cause of your fever, you may or may not require medical treatment for the fever alone. Many experts believe that fever is a natural bodily defense against infection. There are also many non-infectious causes of fever.

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Fever is generally not considered dangerous, but hyperthermia can cause dangerous rises in body temperature. This can be due to an extreme temperature associated with heat injury such as heat stroke, side effects of certain medications or illicit drugs, and stroke. With hyperthermia, the body is no longer able to control body temperature.

In children with fever, accompanying symptoms such as lethargy, fussiness, poor appetite, sore throat, cough, ear pain, and diarrhea are important to relay to your health care provider.

According to the American Academy of Pediatrics, if you have an infant age 2 months or younger with a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or above, you should immediately call your doctor or go to an emergency room because it could be a sign of a potentially life-threatening infection. A doctor's attention is also warranted if a child ages 3 to 6 months has a temperature of 101 F (38.3 C) or above, or for a child over 6 months old with a temperature of 103 F (39.4 C) or higher. High fever can cause febrile seizures in young children.

Causes of Fever

A part of the brain called the hypothalamus controls body temperature, which usually varies throughout the day from the considered normal temperature of 98.6 F (37 C). Normal body temperature is generally a little cooler in the early morning but may reach as high as 99.9 F (37.7 C) by late afternoon.

In response to an infection, illness, or some other cause, the hypothalamus may reset the body to a higher temperature. The substances that cause fever are called pyrogens, which can come from inside the body (proteins called cytokines) or outside of the body (such as germs or their toxins).

Although the most common causes of fever are common infections such as colds and gastroenteritis, other causes include:

Infections of the ear, lung, skin, throat, bladder, or kidney
Inflammatory conditions
Side effects of drugs
Cancer
Routine vaccinations

Other causes of fever include:

Blood clot or pulmonary embolism
Autoimmune diseases such as lupus, rheumatoid arthritis, and inflammatory bowel disease
Hormone disorders such as hyperthyroidism
Illegal drugs that increase heat production such as amphetamines and cocaine