Test Overview

Body temperature is a measure of how well your body can make and get rid of heat. The body is very good at keeping its temperature within a safe range, even when temperatures outside the body change a lot.

• When you are too hot, the blood vessels in your skin widen to carry the excess heat to your skin's surface. You may start to sweat. As the sweat evaporates, it helps cool your body.
• When you are too cold, your blood vessels narrow. This reduces blood flow to your skin to save body heat. You may start to shiver. When the muscles tremble this way, it helps to make more heat.

Your body temperature can be measured in many places on your body. The most common ones are the mouth, the ear, the armpit, and the rectum. Temperature can also be measured on your forehead.

Thermometers show body temperature in either degrees Celsius (°C) or degrees Fahrenheit (°F). The standard in Canada and most other countries is degrees Celsius. In the United States, temperatures are often measured in degrees Fahrenheit.

Why It Is Done

Body temperature is measured to:

• Check for fever.
• Check for a very low body temperature in people who have been exposed to cold.
• Check for a very high body temperature in people who have been exposed to heat.
• Find out how well a fever-reducing medicine is working.
• Help a woman plan for pregnancy by finding out if she is ovulating.

How To Prepare

Take your temperature a few times when you are well. This will help you find out what is normal for you. Check your temperature in both the morning and evening. Body temperature can vary by as much as 0.6°C (1°F) during the day.

Before you take your temperature:

• Wait at least 20 to 30 minutes after you smoke, you eat, or you drink a hot or cold liquid.
• Wait at least an hour after hard exercise or a hot bath.

Glass thermometers that contain mercury aren't recommended. If you have a glass thermometer, contact your local health unit to find out how to dispose of it safely. If you break a glass thermometer, call your local poison control centre right away.

How It Is Done

Oral (by mouth) temperature

Before you take a temperature, read the instructions for how to use your type of thermometer.

Oral (by mouth) is the most common method of taking a temperature. This method can be used for children who are older than 5 years of age. For you to get an accurate reading, the person must be able to breathe through their nose. If they can't, then use the rectum, ear, or armpit to take the temperature.

1. Place the thermometer under the tongue, just to one side of the centre.

   Ask the person to close their lips tightly around it.

2. Leave the thermometer in place for the required amount of time.

   Time yourself with a clock or watch. Some digital thermometers give a series of short beeps when the reading is done.

3. Remove the thermometer, and read it.
4. Clean the thermometer.

   Clean a digital thermometer with cool, soapy water, and rinse it off before you put it away.

Rectal temperature

Before you take a temperature, read the instructions for how to use your type of thermometer.

This is the most accurate way to measure body temperature. It's recommended for babies, small children, and people who can't hold a thermometer safely in their mouths. Use a rectal thermometer only if you are comfortable doing so. It's also used when it is very important to get the most accurate reading. Don't use a thermometer to take an oral temperature after it has been used to take a rectal temperature.

1. Apply a lubricant jelly or petroleum jelly, such as Vaseline, on the bulb of the thermometer.

   This will make it easy to insert.

2. With a baby or small child, turn the child face down on your lap or on a flat surface that's covered or padded, such as a bed. If a baby is unable to safely lie on their stomach, place them on their back.

   Choose a quiet place so that the child won't be distracted or move around too much.

3. Insert the thermometer.
   1. Spread the child's buttocks with one hand. With the other hand, gently insert the bulb end of the thermometer into the anus.
   2. Push it in about 1.25 cm (0.5 in.) to 2.5 cm (1 in.). Don't force it into the rectum.
   3. Hold the thermometer in place with two fingers close to the anus (not near the end of the thermometer).

4. Time yourself with a watch or clock. Some digital thermometers give a series of short beeps when the reading is done.

5. Remove the thermometer and read it.
6. Clean a digital thermometer with cool, soapy water and rinse it off before you put it away.

Armpit temperature

Before you take a temperature, read the instructions for how to use your type of thermometer.

Taking a temperature in the armpit may not be as accurate as taking an oral or rectal temperature.

1. Place the thermometer under the arm, with the bulb in the centre of the armpit.
2. Press the arm against the body, and leave the thermometer in place for the required amount of time.

   Time yourself with a watch or clock.

3. Remove the thermometer and read it.
4. Clean a digital thermometer with cool, soapy water and rinse it off before you put it away.

Ear temperature

Before you take a temperature, read the instructions for how to use your type of thermometer. This method is recommended for children older than 2 years. 

This method is recommended for children older than 2 years. Ear thermometers may need to be cleaned before they are used.

1. Check that the probe is clean and free of debris.

   If dirty, wipe it gently with a clean cloth. Do not put the thermometer underwater.

2. To keep the probe clean, use a disposable probe cover.

   Use a new cover each time you take an ear temperature.

3. Turn on the thermometer, and gently pull the earlobe back.
4. Centre the probe tip in the ear, and push gently inward toward the eardrum.

   Do not force it in.

5. Press the "on" button to display the temperature reading.
6. Remove the thermometer, and throw away the used probe cover.

Temporal artery temperature

Before you take a temperature, read the instructions for how to use your type of infrared thermometer.

1. Remove the cap over the cup part of the thermometer, if it has a cap.
2. Turn on the thermometer.
3. Place the thermometer cup on the skin in the centre of the forehead.

   Make sure nothing is between the thermometer cup and the skin.

4. Press the button for making a measurement.
5. Slide the thermometer across the forehead to one side (not up or down).
6. Listen for a sound.

   Most of these thermometers make a beep or other sound when they are ready to read.

7. Remove the thermometer from the forehead, and read the temperature.

How It Feels

Taking an oral temperature causes only mild discomfort. You have to keep the thermometer under your tongue and hold it in place with your lips.

Taking a rectal temperature can cause a little discomfort, but it should not be painful.

Taking an ear temperature causes little or no discomfort. The probe is not inserted very far into the ear, and it gives a reading in only a few seconds.

Taking a temporal artery, forehead, or armpit temperature does not cause any discomfort.

Risks

There is very little chance of having a problem from this test.

When taking a rectal temperature, do not push the thermometer in more than 1.25 cm (0.5 in.) to 2.5 cm (1 in.). Pushing it farther can be painful and may damage the rectum.

Results

If you tell your doctor about your temperature reading, be sure to say where it was taken: on the forehead or in the mouth, rectum, armpit, or ear.

Comparing temperature types

You can take a temperature using the mouth (oral), anus (rectal), armpit (axillary), or ear (tympanic). But the temperature readings vary depending on which one you use. And you need an accurate measurement to know if a fever is present.

Medical research hasn't found an exact correlation between oral, rectal, ear, armpit, and forehead temperature measurements. In general, a forehead (temporal) scanner is usually 0.3°C (0.5°F) to 0.6°C (1°F) lower than an oral temperature.