Patient education: When to worry about a fever in adults (The Basics)
Written by the doctors and editors at UpToDate
What is a fever?
— A fever is a rise in body temperature that goes above a certain level. The level that is considered a fever depends on how you take the temperature. Here are the values that are considered a fever:
●Oral (mouth) temperature above 100ºF (37.8ºC)
●Armpit temperature above 99ºF (37.2ºC)
●Ear temperature above 100.4ºF (38ºC) in rectal mode or 99.5ºF (37.5ºC) in oral mode
●Forehead temperature above 100.4ºF (38ºC)
●Rectal temperature above 100.4ºF (38ºC)
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. Common infections that can cause fever include:
●A cold or the flu
●An airway infection, such as bronchitis
●A stomach bug
Most of these infections are not serious and get better on their own.
When should I see a doctor?
— Call your doctor if you get a fever and you:
●Are pregnant
●Recently got back from a trip to Africa, Asia, Latin America
●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.
You should also call if you have:
●Fever that lasts several days or keeps coming back
●A recent bite from an insect called a tick – Infections you can catch from tick bites can cause fever and other symptoms.
●A serious health condition, such as diabetes, heart disease, cancer, lupus, or sickle cell anemia
●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 will do an exam and talk with you about your symptoms. You might also have the following tests:
●Blood tests
●Urine tests
●Chest X-ray or CT scan – These imaging tests create pictures of the inside of the body.
Your doctor 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.