7 Types of Thermometers: The Best Way To Take a Temperature

Parents can use many different types of thermometers, including oral, rectal, ear, forehead, and more. Here's how the different methods measure up.

woman looking at thermometer
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A fever indicates your child's body is fighting off an infection. If your little one has a fever, they may be warm to the touch, flushed or sweating, or have chills. Because being bundled in too many clothes or blankets may result in fever-like symptoms, taking your child's temperature is the best and most reliable way to determine whether a fever is present.

Knowing how to use a thermometer to measure your child's temperature is important. Temperatures can be taken in several different places on the body with various thermometers; whichever type of thermometer you use, be sure to read the directions carefully. Almost all thermometers require correct positioning to get the most accurate reading.

Although many fevers run their course without medical intervention, see your doctor if your child's temperature is above 102 degrees Fahrenheit for more than 24 hours or if the fever is higher than 104 degrees Fahrenheit. For infants under 3 months, call the doctor if the fever is over 100.4 degrees Fahrenheit.

When you report a fever to your doctor, always tell them where you took your child's temperature and which type of thermometer you used. Here's how different thermometers measure up.

Rectal Thermometer

Because it's the most internal and, therefore, the most accurate measurement, many doctors recommend taking a rectal temperature in babies and children 3 years of age and younger. To use, first dab petroleum jelly on the bulb of the clean thermometer. Place your baby belly-down on your lap or changing table. You can also position your baby face-up on the changing table, lifting their legs (knees to chest) as though you were changing a diaper. Then gently insert the bulb 1/2 to 1 inch into your child's rectum. Loosely hold the thermometer in place with two fingers until it beeps, making sure your baby doesn't squirm too much.

Oral Thermometer

Placing the thermometer under the tongue in cooperative children over 3 is also accurate, provided the child keeps their mouth closed and refrains from drinking hot or cold liquids 15 to 20 minutes before the thermometer is inserted. The reading can be thrown off if your child doesn't keep the thermometer under their tongue until it beeps.

Ear (Tympanic) Thermometer

Tympanic thermometers, also known as remote ear thermometers, measure the body's temperature through the ear canal using an infrared ray. This type of thermometer can be a great option for kids who are too wiggly or sensitive to sit still with a touch thermometer. However, parents should note that accuracy is easily affected by things like ear wax buildup, ear canal curvature, and how close or far the device is held. The cost for tympanic thermometers varies greatly and while a device for under $20 may be tempting for a watchful budget, make sure to read reviews first. You can ask your doctor what brands they recommend for home use.

Underarm Thermometer

Your child's armpit gives the least accurate reading. However, a thermometer under the arm for four to five minutes is still good in a pinch, especially if your child doesn't let you insert one anywhere else. Many doctors recommend adding 1 degree Fahrenheit to the reading for greater accuracy because the temperature under the arm is generally lower than the temperature at the body's core. If the room is chilly, you may get a false low reading.

Digital Forehead (Temporal) Thermometer

These are fast, fairly accurate, and great to use when your baby is too young to sit still. Make sure that the infrared sensor is near the temporal artery (between the outside edge of the eye and the hairline). Look at the directions carefully to make sure you get an accurate reading.

Similar to the tympanic style thermometer, the temporal thermometer's accuracy is also easily affected by things like direct sunlight, forehead sweat, and how close or far away the device is held while reading a temperature.

Wearable Thermometer

Wearable thermometers can be used continuously and don't require waking or disturbing the child. Their ability to track the fever across time can be helpful. Most wearable thermometers connect to an app to display the temperature reading.

These noninvasive thermometers may sound perfect for kids, but studies have shown they lack consistent accuracy, which can be problematic for kids fighting off a fever. One major issue with wearable thermometers is that they measure skin temperature instead of core temperature. Other factors can also influence the reading, such as the location of the sensor, physical exertion level, and outside temperature.

Forehead Thermometer Strips

Foreheard thermometer strips are the least invasive and disruptive way to take a child's temperature. They work by holding the strip on the forehead until the color registers along the strip. That said, forehead thermometer strips are inaccurate and probably not worth using. According to the University of Oxford in England, under testing, forehead strip thermometers were only accurate 4 out of 10 times, making them ineffective at detecting fevers.

Consider Ditching Mercury

No matter which type of thermometer you choose, you should consider ditching old-school varieties containing mercury. This potent toxin affects the brain, spinal cord, liver, and kidneys and can cause learning disabilities. If it breaks, you risk exposing your family to mercury's harmful vapors. Still, have one lurking in your medicine cabinet? Don't just toss it into the trash. Take it to your pediatrician (they can dispose of it safely), or drop it off at your local hazardous-waste collection site.

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