What is the most accurate thermometer?

On a baby registry for every new or expecting parent is a good, reliable thermometer. But what exactly does that mean and how do you choose from the seemingly dozens of varieties and hundreds of models? And, more importantly, for whatever type of thermometer you choose, how do you use it correctly?

“There are so many different types of thermometers available today that it’s no wonder parents get confused,” says Dr. Markeita Moore, a virtual primary care physician with Advocate Health Care. “To make matters more complicated, a normal temperature range can differ depending on the age of the child, the type of thermometer and where it is used. It’s enough to stress out any parent, especially when they’re dealing with a sick kid.”

Types of thermometers

Now that mercury thermometers are no longer recommended, there are essentially two main types of thermometers: contact thermometers and remote thermometers. But within those two main groups there are still more choices.

Digital contact thermometers

• Use an electronic heat sensor to record body temperature.
• For adults and older children who can tolerate it, digital contact thermometers should be used orally, under the tongue, for the most accurate reading.
• Make sure to wait 15 minutes after eating or drinking for the greatest accuracy.
• For younger children, these thermometers can be used rectally (clean thoroughly after use or use a disposable probe cover) or under the armpit, which will provide the least accurate reading.
• When it’s considered a fever:
  • Mouth: Above 99.4 degrees Fahrenheit is considered a low-grade fever for a baby; above 100 degrees Fahrenheit for a child over the age of 1
  • Rectum: Above 100.4 degrees Fahrenheit for a baby; above 101 degrees Fahrenheit for a child
  • Armpit: Above 98.4 degrees Fahrenheit for a baby; above 99 degrees Fahrenheit for a child

“For parents with wiggly kids, sometimes an armpit reading will have to do,” Dr. Moore says. “In that case, don’t forget to either change the setting on your thermometer to underarm or to subtract about 1 degree Fahrenheit, compared to an oral reading.”

Temporal contact thermometers

• Not to be confused with non-contact infrared forehead thermometers, temporal contact thermometers (sometimes called temple touch thermometers) measure the heat flowing from blood vessels to the skin surface.
• Users typically only need to run the sensor across the forehead.
• A reading is considered a fever when it’s above 98.4 degrees Fahrenheit for a baby; above 99 degrees Fahrenheit for a child.

Ear thermometers

• Also known as tympanic thermometers, ear thermometers measure the temperature inside the ear canal.
• Pull the top of the ear upward to open the ear canal, insert the tip of the thermometer and press the button. Do not insert too far. Excessive earwax can skew temperature readings.
• It’s considered a fever when the reading is above 100.4 degrees Fahrenheit for a baby; above 101 degrees Fahrenheit for a child.

“Though less accurate than rectal or oral thermometers, ear thermometers can make a nice alternative for people with young kids,” Dr. Moore says. “However, do not use this thermometer for children under 6 months old since their ear canals are too small.”

Pacifier thermometers

• Typically used for infants, they are not considered the most accurate way to measure oral temperature.
• Many brands require the infant to suck on the thermometer for at least three minutes.
• It’s considered a fever when the temperature is above 99.4 degrees Fahrenheit for a baby; above 100 degrees Fahrenheit for a child.

Non-contact infrared forehead thermometer

• An increasingly popular choice, these non-contact thermometers measure the temperature of the superficial temporal artery in the forehead.
• Point the scanner at the forehead and press the button. These thermometers are generally less accurate than a standard oral thermometer.
• It’s considered a fever when the reading is above 98.4 degrees Fahrenheit for a baby; above 99 degrees Fahrenheit for a child.

“These are becoming a go-to option, because parents can take their child’s temperature without even waking them,” Dr. Moore says. “But infrared thermometers are notoriously tricky to use, as parents have to hold them at the correct angle and correct distance. Things like sunlight and sweat can impede proper temperature readings.”

Dr. Moore emphasizes that for all methods of taking a temperature, children should not be overly clothed or wearing a hat.

When reporting a fever, tell your health care professional what type of thermometer you used and how you used it.

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