How to take a temperature
How to take a temperature
- body temperature by itself does not tell you how sick your child is
- regardless of whether your child has a fever or not, if you think they are unwell and you are worried, see your doctor
- in babies, an unstable body temperature is very worrying. See your doctor if your baby has either a high or low temperature
- there are a number of different types of thermometers
- there are a number of different places on the body you can measure temperature
- how you measure your child’s temperature depends on their age and the type of thermometer that you have
Why take my child’s temperature?
You might want to measure your child’s body temperature if they feel hot. If they do not seem unwell, you do not need to take their temperature.
The most common reason for a child to have a raised temperature is because they are fighting off an infection. A very young baby can get too hot if they are wrapped in too many layers.
If your child is very young (under three months old) and they have a fever, they should be checked by a doctor.
- for information about fever (high temperature) and what it means, see Fever
- if you are worried about your child, see BabyCheck for children under six months old and Is my child sick? for older children
What am I measuring?
When you take a temperature, you are trying to measure how hot your child is inside their body. This is called their “core temperature”.
You measure the temperature in places that are closest to the inside temperature. You measure the temperature inside the mouth (oral), under the arm (axillary), or in their outer ear canal (tympanic). In hospital temperatures are sometimes measured in the bottom (rectal). We advise that you do not take your child’s rectal temperature at home.
The normal temperature inside your child’s body is around 37 degrees Celsius. Your child’s brain helps control their core temperature and to keep it around that level. After three months of age, body temperature changes with a daily rhythm - rising to 37.3 toward the end of daytime before dropping to 36.8 shortly after going to sleep at night and then slowly coming up to about 37 in the morning. New babies are not as good at controlling their temperature as older children.
We say that there is a fever when the temperature is more than 38 degrees Celsius. A fever by itself does not indicate whether your child is seriously sick or not.
What sort of thermometer should I use, and how do I use it?
Which thermometer you use, and how you use it, depends on the age of your child.
There are many types of thermometers available.
The most common type are the digital thermometers. These can be used at any age from birth. They are easy to use and accurate, and are usually the cheapest.
The electronic ear thermometer is expensive, and it is not suitable for use in small babies.
How to use a digital thermometer
These thermometers are used in a similar way to the old-fashioned mercury-in-glass thermometers, but they are much easier to read. They give a digital read out. They can be used for all ages. There are a number of brands. They are usually the cheapest option. You need to read and follow the instructions that come with your one.
If your child is under five years, you can use the digital thermometer under the arm. If you measure the temperature under the arm, it records about half to one (0.5 - 1.0) degree Celsius lower than the core temperature.
To use a digital thermometer under the arm (the axillary temperature):
- turn it on (these thermometers usually have a button you press to turn on)
- place the end in the armpit against the skin, and bring your child’s arm down over the top of it. It often helps to hug your child to keep the arm down and the thermometer in place
- some thermometers beep while measuring, with a change in the beep when the core temperature is reached; others only beep when the core temperature is reached. To avoid confusion, it is worth keeping the thermometer in place for two minutes.
- remove the thermometer and read the number on the side. The temperature you read is about half to one (0.5 - 1.0) degree Celsius lower than your child’s actual body or core temperature
If your child is five years of age or older you can try to measure the temperature in the mouth (the oral temperature).
To use it in the mouth in older children:
- your child has to be able to co-operate, which usually means they are of school age
- turn it on
- place the end in the mouth under the side of the tongue. Try to get your child to keep it there
- some thermometers make beeping noises when they have finished, but it is worth keeping it in place for at least two minutes
- remove the thermometer and read the number on the side. The temperature you read in in degrees Celsius is close to your child’s actual body or core temperature
How to use an ear thermometer
The electronic or infrared ear thermometer is fast and accurate if it is used correctly. It can be used in older children but is not recommended for use in young babies.
There are a number of brands. They are more expensive than digital thermometers.
Read the instructions for your thermometer to find out how to turn it on and take the reading. When placing the measuring end in the ear, be gentle. You do not have to push it far into the ear canal, just at the entrance.
How to use an infrared forehead thermometer
Infrared forehead thermometers are a new type of thermometer. They are quick and easy to use, as you simply point them at your child’s forehead. They are expensive and it is not clear yet how accurate they are. They measure the forehead skin temperature which changes a lot with blood flow and room temperature.
How to use a mercury-in-glass thermometer
These old style thermometers are no longer available but some households still have them. Mercury vapour can be toxic if the thermometer breaks, so consider getting a new one.
If you do use a mercury-in-glass thermometer, be very careful. You use them the same way you use a digital thermometer, except that, before using it, you hold the thermometer by the end (not the tip) and gently shake it a few times to make the mercury settle down.
Reading the thermometer takes a bit of practice.
How to use a plastic strip thermometer
These are plastic strips that you place on your child’s forehead. They are not accurate, and are not recommended.
Where to go for more information
This website tool, for babies under six months old, might help guide you as to whether you need to take your baby to a doctor. The website has been designed by a neonatal doctor. The other areas of this website (NICU Tools) are aimed at health professionals.
Telephone advice - Healthline and PlunketLine
- ring PlunketLine on 0800 933 922 if you have child health and parenting questions or queries. For example, if you have questions about such issues as parenting, crying, sleeping, your child's growth, development, behaviour, immunisation, breastfeeding, nutrition, oral health, safety or want to know more about the Well Child / Tamariki Ora programme
- call Healthline on 0800 611 116 if you need advice about a child of any age who is unwell or hurt, or has any symptoms of sickness. Healthline provides a full range of telephone triage and health advice for children (and adults)
- both services are available 24 hours and are free to callers throughout New Zealand, including from a mobile phone
The image of the mercury-in-glass thermometer comes from http://www.istockphoto.com/license.php and is reproduced in accordance with the site's Content License Agreement.
Thank you to Dr Greg Williams for providing the other images in this fact sheet.
© Paediatric Society of New Zealand and Starship Foundation 2005 – 2013
Printed on 18 June 2013. Content is regularly updated so please refer to www.kidshealth.org.nz for the most up-to-date version
DISCLAIMERThis fact sheet is for educational use only.
Please consult your doctor or other health professional to make sure this information is right for your child.
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© The Paediatric Society of New Zealand and Starship Foundation 2005 - 2012