A fever is a temporary rise in body temperature. It’s one part of an overall response from the body’s immune system. A fever is usually caused by an infection. For most children and adults, a fever is a body temperature that’s higher than is considered normal. It’s also called a high temperature, hyperthermia, or pyrexia, and it’s usually a sign that your body is working to keep you healthy from an infection. Normal body temperatures are different for everyone, but they lie within the range of 97 to 99. A temperature of 100.4 or higher is considered a fever.
A part of your brain called the hypothalamus controls your body temperature. In response to an infection, illness, or some other cause, the hypothalamus may reset the body to a higher temperature. So when a fever comes on, it’s a sign that something is going on in your body.
Fevers themselves generally aren’t dangerous, but you should check in with your doctor if the fever may be uncomfortable.
The most common causes of fever are infections such as colds and stomach bugs (gastroenteritis).
Other causes include:
- Infections of the ear, lung, skin, throat, bladder, or kidney
- Heat exhaustion
- Conditions that cause inflammation, such as rheumatoid arthritis
- Side effects of medications
- Vaccines and immunizations
- Blood clots
- Autoimmune conditions such as lupus and inflammatory bowel disease (IBS)
- Hormone disorders such as hyperthyroidism
- Illegal drugs such as amphetamines and cocaine
- Teething in babies can cause a mild, low-grade fever (not over 101 degrees)