Patient education: When to worry about a fever in adults (The Basics)

What is a fever? — A fever is a rise in body temperature that goes above a certain level.

In general, a fever means a temperature above 100.4ºF (38ºC). You might get slightly different numbers depending on how you take your temperature – oral (mouth), armpit, ear, forehead, or rectal.

What is the best way to take my temperature? — Armpit, ear, and forehead temperatures are easier to measure than rectal or oral temperatures, but they are not as accurate.

Here is the right way to take an oral temperature:

●Wait at least 30 minutes after you eat or drink anything hot or cold

●Wash the thermometer with cool water and soap. Then rinse it.

●Place the tip of the thermometer under your tongue toward the back. Hold the thermometer with your lips, not your teeth.

●Keep your lips closed around the thermometer. A glass thermometer takes about 3 minutes to work. Most digital thermometers take less than 1 minute.

The height of the temperature is less important than how sick you feel. If you think you have a fever and you feel sick, your doctor or nurse might want you to double-check by getting an oral or rectal temperature.

What causes fever? — The most common cause of fever in adults is infection. Infections that can cause fever include:

●Coronavirus 2019 (COVID-19)

●A cold or the flu

●An airway infection, such as bronchitis

●A stomach bug

Some people can get very sick from COVID-19 or the flu. But most common infections are not serious and get better on their own.

When should I see a doctor or nurse? — Call your doctor or nurse if you live in an area where people have COVID-19. They will ask you questions about your symptoms and whether you might be at risk. They can also tell you if you should get tested for the virus.

You should also call your doctor or nurse if you get a fever and you:

●Are pregnant

●Recently got back from a trip to Africa, Asia, Latin America, or the Middle East

●Just got out of the hospital, or had surgery or another medical procedure

●Get infections often

●Are on chemotherapy – Call your doctor or nurse if your oral temperature goes above 100.4ºF (38.0ºC) for more than 1 hour. Also call if it goes above 101ºF (38.3ºC) even just 1 time.

●Take medicines that suppress the body's infection-fighting system, also called the "immune system" – Examples of these medicines include steroids and medicines used to prevent rejection after organ transplant.

Other reasons to call include:

●Your fever lasts several days or keeps coming back

●You think you were recently bitten by a tick – Infections you can catch from tick bites can cause fever and other symptoms.

●You have a serious health condition, such as diabetes, heart disease, cancer, lupus, or sickle cell anemia

●You have a fever plus 1 or more of these symptoms:

•Rash

•Trouble breathing

•Severe headache or neck pain

•Seizure or confusion

•Severe vomiting or diarrhea

•Severe pain in the belly, back, or sides

•Any other symptom that is unusual or worries you

Will I need tests? — Maybe. Your doctor or nurse will do an exam and talk with you about your symptoms. You might also have the following tests:

●A swab from inside your nose – This can be tested for the virus that causes COVID-19.

●Blood tests

●Urine tests

●Chest X-ray or CT scan – These imaging tests create pictures of the inside of the body.

Your doctor or nurse will talk to you about any other tests you might need.

Can I do anything on my own to feel better? — Yes. You can stay home, rest, and drink plenty of fluids. You can also take acetaminophen (sample brand name: Tylenol) to relieve fever.

How are fevers treated? — That depends on the cause. Many people do not need treatment. If you do, treatments can include:

●Antibiotics to fight the infection. But antibiotics only work on infections caused by bacteria, not infections caused by viruses. For example, antibiotics will not work on a cold.

●Medicines, such as acetaminophen (sample brand name: Tylenol) or ibuprofen (sample brand names: Advil, Motrin). These medicines can help bring down a fever. But they are not always necessary.

More on this topic

Patient education: Fever in children (The Basics)
Patient education: COVID-19 overview (The Basics)
Patient education: Flu (The Basics)
Patient education: Viral gastroenteritis in adults (The Basics)
Patient education: Neutropenia (The Basics)
Patient education: Neutropenia and fever in people being treated for cancer (The Basics)
Patient education: What you should know about antibiotics (The Basics)

Patient education: Foodborne illness (food poisoning) (Beyond the Basics)
Patient education: Infectious mononucleosis (mono) in adults and adolescents (Beyond the Basics)
Patient education: Influenza symptoms and treatment (Beyond the Basics)