Learn How to Use a Thermometer Correctly

Understanding the Different Types of Thermometers

A thermometer is a tool that measures body temperature. Several types exist, and each works in a different way. Understanding the differences helps you choose the right one for your situation.

Digital thermometers are the most common type used in homes today. They have a small screen that displays the temperature in numbers. Inside, they contain a sensor that detects heat. When placed under the tongue, in the armpit, or in the ear, the sensor reads the temperature and shows it on the display within seconds to a few minutes. Digital thermometers are affordable, reliable, and widely available at drugstores and supermarkets.

Infrared thermometers, also called temporal or forehead thermometers, measure temperature by detecting heat radiation from the skin. You hold the device near the forehead and press a button. The reading appears almost instantly on a screen. These thermometers never touch the skin, which some people prefer for hygiene reasons. However, they can be less accurate than other types if not used correctly.

Tympanic thermometers measure temperature inside the ear canal. They work quickly—usually within one to two seconds—by detecting infrared radiation from the eardrum. These thermometers are popular in hospitals and medical offices but are less common in homes.

Mercury thermometers were once the standard but are now being phased out in many places due to health and environmental concerns. Mercury is toxic, and if the thermometer breaks, the mercury can be dangerous. Many countries have restricted or banned their sale.

Practical Takeaway: Digital thermometers are the most practical choice for home use because they are safe, affordable, and straightforward to operate. They provide accurate readings when used correctly.

Preparing Yourself and the Thermometer Before Taking a Reading

Preparation is a crucial step that many people overlook. Taking a few minutes to get ready before measuring temperature leads to more accurate results.

First, wash your hands with soap and water before handling a thermometer. This reduces the chance of spreading germs, especially if you are measuring someone else's temperature. If using a digital thermometer that will go in the mouth, rinse it with cool water and dry it completely. If you are measuring someone else, wash your hands again after touching their skin.

Wait at least 30 minutes after the person has eaten, drunk something hot or cold, smoked, or exercised. These activities raise or lower mouth temperature temporarily and will give a false reading. If the person is very cold or very hot from being outside, wait 15 to 30 minutes before measuring to allow their body temperature to stabilize.

Check that the digital thermometer has fresh batteries and is working properly. You can test this by turning it on and making sure the display lights up and shows numbers clearly. If the screen is dim, hard to read, or the device does not turn on, replace the batteries or consider getting a new thermometer.

If using an infrared thermometer, make sure the forehead area is dry and clean. Sweat, dirt, or hair can block the sensor and cause an inaccurate reading. Gently wipe the forehead with a clean cloth if needed.

Choose a quiet, comfortable place to take the measurement. The person should sit or lie down for a few minutes before you measure. This helps their body settle into a normal state. Stress, activity, or being anxious can raise body temperature slightly.

Practical Takeaway: Spend a few minutes preparing by checking the thermometer works, waiting after meals or hot drinks, and choosing a calm environment. These simple steps significantly improve accuracy.

Using an Oral Digital Thermometer Correctly

Oral thermometers are placed under the tongue and are one of the most common methods of taking temperature at home. When used correctly, they give reliable results.

Turn on the digital thermometer and wait for it to be ready. Most devices show a symbol or make a beep when they are powered on. Hold the thermometer by the handle, never by the metal or plastic tip. Clean the tip with a tissue or cool water if it has been sitting for a while.

Place the tip under the tongue, roughly in the center of the mouth, toward the back. Press the tip gently upward against the roof of the mouth. This position allows good contact with the blood vessels in that area, which gives an accurate temperature reading. Close your mouth firmly around the thermometer and keep it closed. Breathing through the mouth or talking will let cool air in and lower the reading.

Hold the thermometer still and in place. Do not move it around or take it out to check the reading before it is done. Most digital thermometers take about one to two minutes to measure. Wait for the beep or signal that indicates the reading is complete. The time varies depending on the brand and model of thermometer.

When you hear the signal or see a final reading displayed, carefully remove the thermometer and read the temperature shown on the screen. Write down the number and the time, especially if you are tracking temperature over several days due to illness. This record helps doctors if you need to call with questions.

After use, clean the tip with cool water and a tissue, or use an alcohol wipe designed for thermometers. Allow it to dry before putting it away. Never use hot water, as this can damage the device.

Practical Takeaway: Place the oral thermometer tip under the tongue, close your mouth, and keep it still until you hear the signal. Write down the reading and the time for your records.

Using an Underarm and Ear Thermometer Correctly

Axillary thermometers (underarm) and tympanic thermometers (ear) are alternative methods that some people prefer because they are less invasive or quicker than oral measurement.

For underarm measurement, make sure the armpit area is dry. If the person has been sweating, wipe the skin gently with a dry cloth. Remove any clothing from that shoulder if needed. Place the thermometer tip in the center of the armpit, against the skin. Keep the person's arm pressed down against their body to keep the thermometer in place. The tip should be completely covered by skin and arm, not exposed to air. Hold the thermometer steady for three to five minutes, or until the device signals that the reading is complete. Underarm readings are typically about 0.5 to 1 degree Fahrenheit lower than oral readings, so this is normal.

For ear thermometers, gently pull the outer part of the ear upward and backward to straighten the ear canal slightly. This helps the thermometer sensor point directly at the eardrum. Place the tip gently into the ear opening—do not push it in deeply or forcefully. Press and hold the button for one to two seconds until you hear a beep. Remove the thermometer and read the temperature on the screen. Ear thermometers are fast but require proper positioning to be accurate.

Earwax buildup can sometimes block the sensor and cause incorrect readings. If you suspect earwax is present, gently clean the outer ear with a washcloth, but do not insert anything into the ear canal. Some people prefer to take readings from both ears and use the higher temperature, as this may be more accurate.

Both underarm and ear measurements work well for children or people who have difficulty keeping an oral thermometer in place. However, underarm readings take longer, while ear readings can be affected by positioning and earwax.

Practical Takeaway: For underarm measurement, keep the area dry and the arm pressed firmly against the body for three to five minutes. For ear measurement, gently straighten the ear canal before inserting the tip and pressing the button.

Reading and Recording Your Results Accurately

Once you have taken a temperature reading, knowing how to read, record, and interpret the result is important. Normal body temperature is typically between 97°F and 99°F (36.1°C to 37.2°C), though it varies slightly from person to person and throughout the day.

When you see the reading on the digital display, read it carefully. Make sure you are looking at the correct number and the temperature unit (Fahrenheit or Celsius). If the display is hard to see, move to a brighter location or ask someone to help you read it. Write down the exact number shown, the time of day, and the