Medically reviewed by Kristin Hall, FNP
Written by Our Editorial Team
Last updated 8/15/2020
Suffering from a fever is one of the most uncomfortable situations you can be in. C’mon — how can you feel chilled to the bone, but still burning up?
Fevers are your body’s natural defense against invaders — your immune system is fighting a battle, and your comfort (unfortunately) is not a major concern.
But a high fever can also be a sign of a serious medical problem.
Understanding how fevers work and what they could be a sign of will help you determine when you should seek medical advice.
A fever is your body’s way of signaling for help; you should definitely pay attention.
Put simply, a fever (also called pyrexia) is when your body temperature is elevated above normal. But “normal body temperature” differs from person to person. Typically, 98.6℉ is about normal for most people.
You can take your body temperature using a home thermometer, available at most drug stores and online. While it’s possible to test for a fever using an armpit or rectal temperature, most folks find it easiest to take their temperature orally.
Several official medical organizations — including the American College of Critical Care Medicine, the International Statistical Classification of Diseases, and the Infectious Diseases Society of America — define a fever as 100.9℉ or higher.
Regardless of the precise measurement, a fever is your body’s response to an illness or infection. Bacteria and viruses thrive at the normal human body temperature, but a fever makes it difficult for them to survive.
In other words, a fever is a sign that your body is fighting invaders such as a virus or bacterial infection.
There are other possible causes for fevers (more on those below), but most often a fever is a sign that you have an infection of some kind.
Infections. Any number of illnesses can cause a fever. The most common and likely causes include: respiratory tract infections, gastrointestinal infections, skin infections and urinary tract infections.
These classifications would include illnesses such as influenza, COVID-19 (coronavirus), strep throat, sinus infections, ear infections and more. Fevers caused by an acute infection generally last four days or less.
Medications. Several medications can trigger a fever, including blood pressure medications, anti-seizure drugs and antibiotics.
They may do this by interfering with how your body normally dispels heat, interfering with temperature regulation, damaging tissue, stimulating an immune response or because of certain properties within the drug itself.
Make sure to tell your healthcare provider about all of the medications you’re taking, as they’ll be able to help determine if they’re contributing to your fever.
Cancer. Kidney cancer, leukemia and lymphoma can all cause fevers.
Inflammatory disorders. Disorders that cause inflammation in the joints and connective tissues can also cause fevers. Lupus and rheumatoid arthritis are a few examples.
These aren’t the only causes of fevers. Thyroid disorders, brain injuries and more can also trigger an elevation in your body’s temperature.
If your fever lasts longer than a day or two, talking to a healthcare provider may help uncover the source of the fever and get you pointed towards treatment to make you more comfortable and lessen the risks of complications.
In some cases, a fever can be a medical emergency. Red flags that you need to contact a healthcare provider immediately include:
Temperature higher than 104℉
Confusion or other changes in cognitive function
Stiff neck and headache
Low blood pressure
Purplish-red spots underneath the skin
Rapid breathing and/or heart rate
Recent travel to areas where malaria or other infectious diseases are present
Use of immunosuppressants
A healthcare professional will evaluate your other symptoms and possibly order diagnostic tests to rule out serious health concerns.
Fevers are a symptom, so proper treatment depends on proper diagnosis. Once you know what’s causing the fever, your healthcare provider will help determine the best course of action to treat the underlying illness.
If the fever is uncomfortable, your healthcare provider may suggest taking an over-the-counter nonsteroidal anti-inflammatory drug (NSAID) such as ibuprofen (Advil®), acetaminophen (Tylenol®) or naproxen. These can lower the body’s temperature while the underlying cause of the fever is addressed.
For example, if your fever is caused by strep throat, an antibiotic may be necessary to fight the infection.
Insider tips, early access and more.