How to take your kid’s temperature

When your little one is sick, one of the most important things you can do—besides cuddle on the couch—is to take your kid’s temperature. Figuring out if your child has a fever and keeping tabs on how long it lasts will help you know if they need medication or if you should be taking them to get checked out by a healthcare provider.

But what might seem like a simple task is complicated by the wide range of devices out there, from the mercury thermometer in grandma’s medicine cabinet—which you should never use because it can break and release poisonous vapour—to a wearable thermometer that continuously monitors your child’s temperature and sends updates to your smartphone.

Here’s what you need to know about the different types of thermometers and how to use them.

Digital thermometers

Digital thermometers are the basic ones you find at the pharmacy for $10 to $20. The Canadian Paediatric Society (CPS) says that digital thermometers are the best devices for taking a kid’s temperature, but the way you use them depends on the age of the child. A rectal thermometer (yup, in the bum) is the first choice for kids under five.

“Even though parents might be slightly uncomfortable with this method, the bottom line is that rectal temperatures are the most accurate,” says Lenora Brace, a nurse practitioner in Pictou County, Nova Scotia, and president of the Nurse Practitioner Association of Canada. It’s especially important to get an accurate reading in babies less than six months old because illnesses can affect them more seriously, as their immune systems are still developing, and they should be seen by a healthcare provider sooner.

If your kid is really resisting a rectal reading, you can take it in the armpit. Kids under five often have trouble holding thermometers under their tongues long enough to get an accurate reading. After age five, experts say it’s best to use a digital thermometer under the tongue, as kids this age will likely resist a rectal reading. Again, the next best place is the armpit.

How to use a digital thermometer

Start by washing the tip of the thermometer in cool, soapy water and rinsing it thoroughly. If you’re taking your kid’s temperature rectally, cover the tip of the thermometer with petroleum jelly, put your child on their back with their knees bent and gently insert the thermometer about 2.5 centimetres.

To get an oral reading, wait 15 minutes after your kid has had anything to eat or drink, place the tip of the thermometer under their tongue and ask them to close their mouth. For an armpit measurement, place the tip of the thermometer in the middle of your child’s armpit and ensure that they keep their arm snug against their body—you can help by gently holding it in place.

Regardless of what method you use, digital thermometers typically need to be held in place for between five seconds and one minute before they beep and display a reading. Your child has a fever when their armpit or oral reading is over 37.5C or their rectal reading is over 38C.

Ear (tympanic) thermometers

If you’re standing in the thermometer section at the pharmacy, you may notice infrared ear devices and wonder if they’re worth the much heftier price tag (they’re often two or three times as much as basic digital thermometers).

For children two and older, the CPS considers this method to be a solid second choice on par with the digital armpit method, as long as it’s used correctly. However, it’s not recommended for children under two because their ear canals are too small.

One of the big benefits of ear thermometers is that they only take a few seconds to register a reading. “When you’ve got a grumpy, sick kid, you want to get in and out pretty quickly with your temperature readings, so the ear thermometer can be a really nice option,” says Mike Dickinson, a paediatrician in Miramichi, New Brunswick, and past president of the Canadian Paediatric Society.

Excess earwax or an ear infection can interfere with a reading, though not significantly, according to the CPS. Poor positioning of the device or a wiggly child can also affect accuracy, but they aren’t major hurdles and most parents can figure them out pretty quickly, says Dickinson.

How to use an ear thermometer

Some devices come with disposable probe covers, so start by slipping one on or cleaning the probe with alcohol if it doesn’t call for a cover. Gently tug your kid’s earlobe to straighten the ear canal, insert the thermometer until the ear canal is closed off and hold down the button for a second. Every model of thermometer is different, so it’s important to follow the directions closely. If you’re worried that an ear infection or earwax may affect the reading, Dickinson recommends taking your child’s temperature in both ears to cross-reference them. A reading of 38C or above is considered a fever.

Forehead (temporal artery) thermometers

Like something straight out of Star Trek, infrared temporal artery thermometers are simply scanned across your child’s forehead to deliver a temperature reading in seconds. Your kid doesn’t even need to be awake, which makes them very appealing to parents.

“It’s an up-and-coming technology that’s showing a lot of promise,” says Dickinson. “I’m not sure we’re quite at the stage yet where we’re comfortable saying it’s as good as the other tried-and-tested methods. We’re still trying to get a feel for it.”

Temporal thermometers are typically in the same price range as ear thermometers or slightly more expensive. Charlie Wharton, a nurse practitioner in the emergency department at SickKids in Toronto, says that, based on his experience, temporal thermometers may be a better tool for parents because there aren’t any barriers (like earwax) to getting an accurate reading.

How to use a forehead thermometer

Different models call for different techniques, so it’s important to read the instructions before you begin. Some thermometers are held on or near the centre of the forehead, while others are scanned across the forehead. Your child should have the same ambient temperature for about 10 minutes without eating, drinking or being physically active before taking their temperature. Their forehead should be clean, with their hair out of the way. Check the instructions to see what temperature constitutes a fever.

Wearable thermometers and apps

If you’re a Fitbit fanatic, this may appeal to you: a wearable thermometer that continuously monitors your child’s temperature and sends data to your smartphone or tablet via Bluetooth. In recent years, several models have come on the market, but research on their safety and effectiveness is lacking.

“There’s no benefit at home to constant temperature measurement for a child,” says Wharton. “It’s more likely to cause anxiety than help you make decisions about whether to treat a fever or seek care.”

Fever strips, which are like Band-Aids that go on the forehead, aren’t recommended because they measure skin temperature rather than core temperature and aren’t accurate.

Pacifier thermometers are also discouraged because they can be affected by how fast the child is breathing, if they have had anything to eat or drink recently and how willing they are to suck on the device (some babies just don’t like pacifiers).

If you’re the type of person who loves the idea of a thermometer app and wants to try out wearables, Dickinson advises you to also take your kid’s temperature with a proven device and not get distracted by the technology. “Parents should be careful to not be hypervigilant about temperature to the exclusion of other, more important symptoms,” he says. “A fever isn’t necessarily dangerous. It’s just a marker of your child’s infection, so people need to put it in context.”