How Can You Help?
Share your StorySupport UsGet Resources

Taking Your Temperature – What Is the Best Way?

May 19, 2021

If you feel hot, cold, feverish, chilly – you may have a fever. You could have just one of those sensations or all within moments of each other. Many experienced parents rely on touching their child’s face to determine if they have a fever, but the only accurate way to know is to take the temperature with a thermometer. But not all thermometers are equal, so how can you ensure you get an accurate body temperature?

From Water Thermoscopes to the Thermometers of Today

The medical thermometer – one of the most commonly used and recognized devices in medicine – has been around for centuries. The first known one, called a water thermoscope, was invented by Galileo Galilei in the 1500s. This was followed by many others using other liquids, like alcohol.

Many of us are familiar with mercury thermometers – the glass tubes we had to shake down every time we wanted to use it. Gabriel Daniel Fahrenheit was the first to apply a scale to a thermometer using mercury instead of water or alcohol. This was followed by many other styles, including one designed by Anders Celsius, who improved the design.

Mercury is a highly poisonous substance and the glass thermometers broke easily, allowing mercury into the environment. This led to a push to develop new ways of taking the body’s temperature. Mercury thermometers are no longer sold and people who still have them in their home are encouraged to dispose of them in a safe manner.

Contact Thermometers

The thermometers most of us are familiar with today are contact thermometers. These thermometers must make and maintain contact on the skin or in the body to register the temperature.

The most precise body temperature reading comes from the rectum, followed by the mouth. Armpit temperatures should only be done if there is no other option, as these are not as accurate.

The drawback to this type of thermometer is they can take longer to register, and if the person being monitored isn’t cooperative, you can’t take their temperature.

Remote Thermometers

Since the COVID-19 pandemic began, we started seeing more infrared thermometers, either in person or on the news. These thermometers take the temperature from the forehead or in the ear. They allow the person taking the temperature to avoid making contact with the person they are evaluating.

The forehead infrared thermometers are convenient and fast, usually only taking seconds for the temperature to be recorded. However, they do have drawbacks, including potential inaccurate readings. For example, someone’s skin may be warm – or hot – for reasons other than a fever. They may have just come inside after being out in the sun or they may be having a hot flash, for example. This would give the thermometer a higher reading than the actual body temperature.

Tympanic thermometers, that measure through the ear, tend to be more precise, faster to use, and seem to be particularly useful with children. The drawback is that if someone has small ear canals or a lot of earwax, the temperature may not be accurate.

What Is a Normal Body Temperature?

We’ve all heard that a normal body temperature is about 98.6° Fahrenheit or 37° Celsius. But this isn’t always the case, as everyone’s body temperature may be slightly different. And even in the same person, body temperature can vary throughout the day. It is often lower in the morning, increasing as the day passes.

Despite the variations, the usual definition of a fever is a body temperature of 100.4°F or 37°C.

Taking a Temperature with a Contact Thermometer

The procedure to take a temperature is easy. After washing your hands with soap and water, and ensuring the thermometer is clean (according to the manufacturer’s instructions), choose which method you will use to take the temperature.

Important note: Consistency is more important than the actual number the thermometer provides. This means to use the same method (oral, rectal, under the arm) each time. The rectal temperature will always be warmer than the under-the-arm temperature, so they can’t be compared.

By mouth:

  • The person whose temperature you are taking should not drink or eat for about five minutes beforehand. The heat or coolness from the food or drink will affect the outcome.
  • Place the tip of the thermometer under the tongue, slightly off to the side. The tongue should then rest on the thermometer, covering it, until the thermometer starts to flash or beep.
  • Register the temperature and clean the thermometer for the next use.

By rectum:

This is the best method for infants and for people who need very accurate temperature readings.

  • Ensure the thermometer is meant for rectal use. You can’t use one meant for oral use.
  • Place the child on their stomach, either on your lap, or a changing table. Carefully insert the thermometer into the rectum but do not force it if you feel any resistance. Do not insert it too far.
  • Wait until the thermometer beeps or flashes.
  • For adults, place the person on their side with one knee drawn up to their chest, if possible, to insert the thermometer.
  • Record the temperature and clean the thermometer, according to manufacturer’s instructions.

By underarm:

You may use an oral thermometer for this method.

  • Remove the shirt and place the tip of the thermometer under the arm, in the center of the armpit.
  • Gently lower the arm to help hold it in place. It may be helpful to have the person cross their arm across the chest.
  • When the thermometer beeps or flashes, record the temperature and clean the thermometer.

Using an Infrared Thermometer

Because different devices have different instructions, always follow the instructions that come with your thermometer. General instructions include:

  • Wait for the device to power up before using it.
  • Point the device at the intended part of the body (forehead, side of the head, or ear).
  • Hold the device still for the number of seconds recommended by the manufacturer.
  • Read the temperature.
  • Clean the device.

The Centers for Disease Control and Prevention (CDC) recommends that if the temperature registers as below 35°C, it should be taken again.

If There Is a Fever

Most people who have a fever can be kept comfortable with over-the-counter medications. The exception is if you have been told to avoid these medications.

Teens should never be given Aspirin for a fever as there is a rare but life-threatening condition called Reye’s syndrome, associated with viruses and Aspirin in this age group.

If a child under the age of three months has a fever, speak to your doctor as soon as possible.

Other reasons to go to an emergency room or to contact your doctor is if the temperature is associated with:

  • Fever not going away or is climbing
  • Seizures, convulsions
  • A stiff neck
  • Severe headache
  • Confusion
  • Any symptoms that are either worsening or are concerning to you
  • Signs of sepsis

It’s About TIME™

Sepsis Alliance put together a memory aid to help people understand some of the more common sepsis symptoms, one of which is temperature. If the fever – or lower than normal body temperature – is associated with an infection, changes in mental status, or a feeling of extreme pain or illness, this could be sepsis. Seek help immediately and say you are concerned about sepsis.