"Mummy, I feel sick!" It's a cry that's all too familiar to most parents. A hand on your child's forehead is a good first step when checking for fever, but for a proper measurement you'll need a thermometer.
What is a fever?
Fever, an elevated temperature above the normal range, is a typical symptom of disease. It's often defined as an oral temperature over 37.5°C for mild cases, or over 38.2°C in more severe cases. Fever passes as the body fights off the disease, but babies with fever – especially those under three months of age – must be checked by a doctor in case the illness is serious. Always seek medical advice if you're concerned about your child's temperature or health.
Know your 'normal' temperature
Normal temperature ranges are slightly different for babies, toddlers, older kids, adults, and the elderly. They can vary a lot; the "normal" temperature of 37°C is only approximate and varies from person to person, and can also be dependent on time of day. Temperature also tends to be lower in the morning and higher in the evening – a variation of 0.5°C is typical.
The best method to determine an individual's normal temperature is to use the thermometer when the person is feeling well. Record readings twice a day (early morning and late afternoon) and take the average of the two temperatures.
You have several options when choosing a thermometer to check temperatures (and you won't find old mercury or alcohol models on most retail shelves these days).
Digital probe thermometers are accurate and cheap.
Used for oral, armpit or rectal readings, digital probe thermometers are the most commonly available type of thermometer. Features vary depending on what you pay for, but they can include a fever alert indicator, large display and a recall of the last reading.
- Accurate for oral and rectal readings, often up to 0.1°C.
- Relatively cheap.
- Some can give oral results in as little as 8–10 seconds.
- May take up to two or three minutes for some models to give a result for armpit (axillary) readings, so may not be suitable for restless babies or children.
How much they cost: $10–$20.
How to get the most accurate reading from a probe thermometer
In general, a person should be still when their temperature is taken. Avoid taking temperatures immediately after your child (or an adult) has exercised or taken a shower or bath, as these temporarily affect body temperature. How you take a reading will also depend on where you're taking the temperature.
The person whose temperature is being taken should not eat or drink for 15 minutes beforehand, as both can affect mouth temperature. Put the probe at the back of their mouth under the tongue and keep their mouth closed until the reading is complete.
Lay your child on their side or, for an infant, on their stomach with legs hanging, such as over your knees. Lubricate the thermometer tip with petroleum jelly and insert it gently about one centimetre into the rectum. Temperature readings are usually 0.5°C higher than for an oral reading.
Ensure the armpit is clean and dry. Place probe in the armpit with tip touching skin and position the arm next to the body to ensure room air doesn't affect the reading. You could gently hug your child to keep their arm in place. These readings are usually 0.5°C lower than for an oral reading.
Handling the thermometer after use
- You should always sterilise a probe thermometer after use, especially when it has been used for rectal readings.
- Check the instructions for specific advice on how to clean your thermometer.
- Usually, you can wipe thermometers with a soft cloth and warm water/mild detergent. Do not immerse in water unless the instructions state otherwise. Sterilise the probe with alcohol but avoid alcohol contact with the battery/display end of the thermometer.
- Use of a disposable sheath on the probe tip minimises spread of bacterial and viral infections.
Ear thermometers are quick but must be positioned correctly.
Ear thermometers are inserted into the ear canal and use infrared rays to read the core body temperature. The temperature is calibrated to be used with a disposable probe cover intact, which keeps the thermometer hygienic.
- Quick to use.
- Less invasive than digital probe thermometers.
- While a good ear thermometer can be accurate, they must be carefully positioned to get an accurate reading. That may be hard if the thermometer is not shaped to suit the eardrum, or if your child's ear canal is too small.
- Either ear may show a different reading, and there must not be any built-up earwax.
- Not generally recommended for infants under six months.
- Need to factor in the ongoing cost of the probe covers, which are single-use only.
How much they cost: $20–$120, plus probe covers ($18–21 for a pack of 40 depending on the brand).
Forehead thermometers are non-invasive but results can vary.
Forehead thermometers use an infrared scanner to measure the temperature of the temporal artery in the forehead.
- Quick (it takes one to three seconds for a result).
- Some are 'touchless' – these are handy for a sleeping infant and can limit the spread of germs.
- A good indicator of temperature, but generally not as accurate as a digital probe thermometer.
- Temperature variations may appear depending on skin type, skin colour, whether the person is wearing make-up, or sweat.
- They aren't always easy to use.
- They aren't usually considered accurate for use on infants under three months.
How much they cost: $30–120.
Some thermometers combine multiple functions.
A plastic strip with heat-sensitive crystals that change colour to give a temperature reading. Temperature strips are very easy to use, but not very accurate. They cost around $10 or less.
These thermometers contain mercury (a silvery-grey liquid metal) or alcohol (usually coloured red). They're cheap and accurate, but nowadays are more likely to be found in an old first aid kit than on a chemist's shelves. They're harder to read than digital thermometers, and there's a risk of poisoning if they break and release their contents.
Other types of thermometers
- We previously reviewed the Nurofen 'FeverSmart' thermometer which used a Bluetooth-enabled temperature monitor placed under your baby's armpit with an adhesive patch. It connected to an app to continually track your baby's temperature but at $140 plus $10 for a four-pack of single-use adhesives, it wasn't cheap.
- Some thermometers have multiple functions such as both ear and forehead functionality, or both forehead and touchless modes.
Regardless of which type you choose, always read the instructions to make sure you know how to use the thermometer correctly and get the most accurate reading.
For instance, it's a good idea not to consume anything for half an hour before using an oral thermometer, in case hot/cold foods influence the reading. Similarly, exerting yourself may mean that sweat can influence the accuracy of a forehead thermometer.
If you're unsure, get your doctor to show you the best way to use the thermometer.
Rather than wait until someone is sick until you use your thermometer for the first time, you can find out what constitutes a 'normal' temperature for you or your child by noting down multiple readings when you're healthy.
Some ear and forehead thermometers use an algorithm to convert the temperature to an oral temperature equivalent, while others may display a slightly higher 'core' temperature. It isn't always clarified in the instructions. Your baseline might also be different depending on other variables such as gender, age, skin type, skin colour, and the ambient temperature.
CHOICE has confirmed that good digital probe thermometers can meet their claimed accuracy to within 0.1°C.
Ear and forehead thermometers are accurate enough, though they usually don't claim to be quite as accurate as digital probes – accuracy to within 0.2°C is the typical claim. Correct usage is the key to getting an accurate reading, so read the instructions or get a medical expert's advice.
Time to reading
Probe models generally deliver a reading in less than 60 seconds. Most models wait until the thermometer reaches a stable temperature then emit a tone and display the reading, but some use a predictive method, meaning they take a partial reading and calculate the final temperature based on mathematical modelling. This makes them faster than most other models, and according to CHOICE tests, just as accurate.
Infrared ear and forehead thermometers usually give a very fast reading, often within three seconds or less, making them easier to use on a restless child. The Nurofen FeverSmart takes eight minutes to 'warm' up.
The larger the display, the easier it is to read. Ideally it should be backlit, too, so you can take a reading at night.
Audible beeps indicate when the thermometer is ready to take a reading, and when it has finished. Many models also let you turn the sound off, which is handy if you want to avoid waking a sleeping infant.
Some models have a distinct tone and/or colour-coded display to show when the patient's temperature is above normal.
This is useful for comfort, particularly when taking rectal temperatures.
This is for protecting the thermometer when it's not in use.
Many models can recall at least one previous reading, some as many as 35. This is good to detect whether temperature is improving or stabilising.
For a digital probe thermometer, disposable sheaths help keep the thermometer clean and hygienic, which is useful if you have to take readings from more than one person, though wiping the probe with sterilising alcohol between readings will also do the trick. Ear thermometers also have compatible, disposable covers, which are typically required to be in place before they can be used (they're also calibrated to work with the covers placed). They can cost between $18–21 for a pack of 40. Always keeps probe covers away from infants as they may pose a choking hazard.
It's important that you, the adult user, can easily access and change the battery when needed, but you don't want your child to do that. Many digital probe and infrared thermometers use button batteries, which are very dangerous if swallowed. After a lengthy CHOICE campaign, products sold in Australia now have to adhere to a mandatory button battery standard. So always keep thermometers and any spare batteries well out of reach of young children and don't let them use thermometers unsupervised.
Our thermometers review lists the battery type required for each model.
Stock images: Getty, unless otherwise stated.