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When your child is running a fever, it’s a sign that their body is trying to fight an infection1. A child’s age determines the best way to take their temperature – for children under age 2, the rectal method is first choice and axillary (armpit) second; for ages 2-5, the rectum, ear, or armpit; while the oral method is first choice for over-5s able to hold the thermometer under their tongue for long enough2,3.

The axillary (armpit) method is usually used to screen whether or not a child has a fever – but if it signals a high temperature, it should be rechecked with a more accurate oral or rectal reading, according to the child’s age3,4.

You can treat an older child at home, providing you give enough liquids and they appear generally well2. See your child’s healthcare provider if the fever lasts for more than 72 hours2.

A word about babies and toddlers…

Babies aren’t yet able to regulate their body temperature and toddlers are also more sensitive to temperature5. Your baby or toddler may have a high temperature if they show signs such as feeling hotter to the touch, on their forehead, back or stomach, feeling sweaty, or having flushed cheeks1. Babies younger than six months must see a healthcare provider when they have a fever2. 

What type of thermometer should I use?

Digital thermometers use electronic heat sensors to record body temperature and can be used in the rectum (rectal), mouth (oral) or armpit6. They work much faster than the old mercury thermometers and are more accurate3,4. Oral and rectal digital thermometers have different shapes and you should never substitute one for the other4. Using an oral thermometer in the rectum can cause injury – so rectal thermometers have a security bulb designed specifically for taking the temperature safely4.

Warning: Never use an old-fashioned glass thermometer1,4,6. These can break, releasing glass splinters and poisonous mercury1.

Ways to take a temperature

In all cases, first check that the digital thermometer is switched on6.

Rectal (in the rectum)

Coat the tip of the clean thermometer with petroleum jelly6. Put your baby tummy down, holding them in place with one hand4,6. Or put them face-up, bend their legs towards their chest and secure them by holding the back of the thighs with one hand3. Insert the thermometer gently ±1,3 cm – 2,5cm into the rectum4,6. Don’t force it if you feel resistance3. Hold the thermometer steady until it beeps (usually ±30 seconds), then remove and check the reading3.

Oral (by mouth)

Place the end of the clean thermometer under the back of the tongue6. Leave it there until it beeps. Remove the thermometer and check the reading. Always wait until at least 15 minutes after eating or drinking to take an oral reading6.

Axillary (under armpit)

Place the digital thermometer under the child’s armpit, touching the skin, not the clothing6. While taking the temperature, hug your child so their arm is tucked tightly against their body until you hear the beep, at which point you can remove the thermometer and read the temperature6.

Tympanic (in the ear)

Although this method is quick, it can give inaccurate readings if inserted incorrectly1. Always read the manufacturer’s instructions so you insert the thermometer the correct distance into the ear canal6. Hold it in place firmly until you hear the beep6.  You can then read the temperature6.

Temporal artery (forehead)

This newer method, which measures the temperature of blood flowing through the temporal artery, is considered very accurate5. It’s also more comfortable than a rectal thermometer and more calming for babies5. You place the thermometer sensor in the middle of your child’s forehead and then press and hold the scan button5. Keep the thermometer in direct contact with the skin while you slowly move it across their forehead towards the top of the ear5. Stop at the hairline before removing the thermometer and reading the temperature5.

Tip: Clean the thermometer with warm, soapy water before and after using3.Don’t bundle up your child too tightly beforehand, check that they’ve not been in a very warm room, been very active, and don’t have a hot water bottle against their body1. Never leave a child unattended with a rectal thermometer inserted4.

What is a normal temperature?2

MethodNormal temperature range
Rectum36,6 °C – 38 °C
Mouth35,5 °C – 37,5 °C
Armpit36,5 °C – 37,5 °C
Ear35,8 °C – 38 °C


  1. NHS. Staff overview. How to take your baby’s temperature. Available at
  2. Canadian Pediatric Society. Staff overview. Fever and Temperature Taking. Available at
  3. Cleveland Clinic. Staff overview. Thermometers: How to Take your Temperature. Available at
  4. Johns Hopkins Medicine. Staff overview.  Measuring a Baby’s Temperature. Available at
  5. NHS North East Essex Clinical Commissioning Group. Staff overview. Staying well in hot weather – tips for parents and guardians. Available at
  6. Mayo Clinic. Staff overview. Thermometer basics: Taking your child’s temperature. Available at