How to Properly Take Someone's Temperature—and How to Know When It's a Fever

Newsflash: Not all temperatures above 98.6 are a fever, and not all thermometers work the same. Here's what you need to know.

You may be thinking, how hard is it to actually take a temperature? A recent study by Braun Thermometers and Wakefield Research revealed that 73 percent of parents believe that any temperature above 98.6 is a problem, significantly more than the 47 percent of child-free adults who say the same. The truth is, a fever is 100.4 or higher.

Taking temperatures isn't rocket science, but there are a few things you should know to get the most accurate reading possible.

how-to-take-temperature: woman in bed checking her temperature
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Get a baseline temperature for the whole family.

A true fever is a reading of 100.4 or higher, but we all have a slightly different baseline temperature. Sure, 98.6 may be average, but that doesn't mean it's the only normal temperature reading. Genetics, time of day, physical activity, and even food and beverage can impact a temperature.

"Getting to know your baseline temperature each day is a good idea," says Tanya Altmann, MD, FAAP, a pediatrician and founder of Calabasas Pediatrics & Wellness Center. "If your child runs 98.9 consistently each day and 99.8 the next day, it may be smart to monitor them for an hour to see if it increases." Everyone's temperature goes up in the afternoon, so it's not a bad idea to do a reading twice a day.

When in doubt, wait it out and call your physician with any concerns.

Know which thermometer to use.

Oral, rectal, ear, forehead, under the arm, no-touch—there are so many ways to take your temperature. All of them work, to varying degrees.

Dr. Altmann says ear thermometers are the most accurate means of taking someone's temperature. "The ear drum reflects the core body temperature most accurately because it's the same blood supply as the hypothalamus that regulates the temperature in the body," she says. Doctors will often take temperatures in the ear for that reason, however, be careful at home not to push too far and cause damage to the ear drum.

For small babies, many physicians still recommend taking the temperature rectally.

Under the tongue and under the arm have become less popular methods of taking a temperature. However, this may be the easiest way to get a reading in some adults or kids. With oral, it's important to keep in mind that eating anything hot or cold could greatly impact the reading. "The recommendation is to wait 30 minutes to an hour after eating when taking an oral temperature," says Monique Dieuvil, MD, a family medicine specialist with Orlando Health Physician Associates.

Taking a temperature on the forehead is often the easiest option for a squirmy kid (or a sleeping one!) and has become commonplace, but sometimes you'll get different readings three times in a row. If kids and babies are wearing hats, in the car seat, or really active before their reading, wait 15 to 20 minutes before using this method.

A newer technology that has really seen popularity is the non-contact infrared forehead thermometer. William Yates, MD, a former trauma surgeon and current owner of Yates Enterprises, which provides security and safety solutions to schools and other venues, is a huge fan of these, especially if you are using them on multiple people or in a school setting.

"Measuring the temperature about one inch from the forehead or temple area on an individual's face using an infrared thermometer provides for the most accurate temperature read," Dr. Yates says. "Keep in mind, forehead thermometers usually will read a temperature approximately one degree lower than a core body temperature, such as oral or rectal."

And if you still own a mercury thermometer, it's time to throw it out. They are no longer recommended in any situation due to the toxicity of mercury.

When you're concerned about fever, tell your doctor the temperature and the type of thermometer you used. "So many parents call my office and self-adjust the temperature readings one or two degrees," says Dr. Altmann. "Just read your doctor exactly what it says and let them take things from there."

Stay home if there is a fever.

A fever in adults or older kids is certainly worth a call to the doctor, and a good reason to stay home from school or work. However, there is no need to panic. Just be sure to assess other symptoms and monitor how your sick loved one is acting.

However, in babies under 3 months old, anything over 100.4 can often be concerning, so call your doctor immediately.

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