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Learning About Fever

Two types of thermometers

What is a fever?

A fever is a high body temperature. It's one way your body fights being sick. A fever shows that the body is responding to infection or other illnesses, both minor and severe.

A fever is a symptom, not an illness by itself. A fever can be a sign that you are ill, but most fevers are not caused by a serious problem.

You may have a fever with a minor illness, such as a cold. But sometimes a very serious infection may cause little or no fever. It is important to look at other symptoms, other conditions you have, and how you feel in general. In children, notice how they act and see what symptoms they complain of.

What is a normal body temperature?

A normal body temperature is about 37ºC. Some people have a normal temperature that is a little higher or a little lower than this.

Your temperature may be a little lower in the morning than it is later in the day. It may go up during hot weather or when you exercise, wear heavy clothes, or take a hot bath.

Your temperature may also be different depending on how you take it. A temperature taken in the mouth (oral) or under the arm may be a little lower than your core temperature (rectal).

What is a fever temperature?

A core temperature of 38°C or above is considered a fever.

What can cause a fever?

A fever may be caused by:

  • Infections. This is the most common cause of a fever. Examples of infections that can cause a fever include influenza (flu), a kidney infection, or pneumonia.
  • Some medicines.
  • Severe trauma or injury, such as a heart attack, stroke, heatstroke, or burns.
  • Other medical conditions, such as arthritis and some cancers.

How can you treat a fever at home?

  • Ask your doctor if you can take an over-the-counter pain medicine, such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), or naproxen (Aleve). Be safe with medicines. Read and follow all instructions on the label.
  • To prevent dehydration, drink plenty of fluids. Choose water and other clear liquids until you feel better. If you have kidney, heart, or liver disease and have to limit fluids, talk with your doctor before you increase the amount of fluids you drink.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse advice line (811 in most provinces and territories) if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Where can you learn more?

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Care instructions adapted under license by your healthcare professional. If you have questions about a medical condition or this instruction, always ask your healthcare professional. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.