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:
●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:
•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:
●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.