Written by:

Dr Sarah Montgomery-Taylor

BM BCh, BA (Oxon), MRCPCH

Dr Montgomery-Taylor is a paediatrician working in London with particular clinical interests in acute paediatrics. Her wider areas of research include child public health, delivery of integrated care, and digital health.

Taking your child’s temperature

In this article:

  • What causes a high temperature?
  • How do you measure temperature?
  • Main Points
  • References

Taking your child’s temperature

High temperature in children is common. Normal baby and child temperature is between 36.5 and 37.5°C and is considered high if it is 38°C or above; this is also known as fever. Babies and young children often develop infections and this may lead to a temperature. What can be challenging is that there are lots of different types of infections and it can be hard for parents to know why children have temperatures and what infection has caused it. Most temperatures in children are not serious and can safely be managed by parents at home. Some can be more severe, especially in babies, and may need urgent treatment in hospital. This article will help you further understand what causes fever and how you should measure it. You can also read this article on managing a temperature for more information on what simple treatments you can give at home and, importantly, what you should look out for to know whether your child needs to get an urgent medical review.

What causes a high temperature?

Temperatures occur as a normal part of the body’s immune response to an infection. Not all infections cause a temperature, particularly in milder cases, although very young babies may also not develop fever even with a more severe infection. Babies and children commonly get infections as their immune system is still developing, particularly the ‘memory’ cells, which remember and fight off infections once the body has already responded to them before. Babies and children are also often in close contact with lots of others who also have infections, particularly in nurseries and schools, and these infections get passed around easily.

Other situations that can cause temperatures in children include having routine immunisations. The health professional giving the vaccination should warn you if this is the case. Even if your child has had immunisations, if they show any of the worrying signs described, later on, it’s important to take them to be seen by a health professional in case there is another more serious cause for this as well. Other inflammatory conditions and reactions to some medications can also cause fever, but these are less common.

The main groups of bugs which cause infection are viruses and bacteria. As a general rule, the most common infections affecting children are viruses, while bacterial and other infections are less common. An area of confusion is around the difference between viruses and bacteria and how they are treated – see the table below for some examples of popular misconceptions.

False True
All infections can be treated with antibiotics Antibiotics only work for bacterial infections
Antibiotics have no side effects Antibiotics often cause diarrhoea and repeated use can cause bugs to become resistant to them
Temperatures that last longer than a day or two must be caused by bacteria Both viral and bacterial infection can be long in duration although fever caused by most common viral infections usually lasts 12-48 hours
The higher the temperature, the more likely it is to be bacterial Both viruses and bacteria can cause very high temperatures
Most infections in children are bacterial Most infections in children are viral
Bacteria and viruses infect very different sites in the body Most infection sites in the body can be caused by either bacteria or viruses – for example chest infections
Nothing can be done to prevent infections Routine immunisations protect against certain viruses and bacteria
Only bacteria causes serious infections Both bacteria and viruses can cause serious infections

Although this may help to clear up some common areas of misunderstanding, you may also be left wondering how parents and doctors can ever tell the difference between the two. The answer is that it can be difficult, and doctors will often need to consider lots of different aspects of your child’s illness – they may examine your child and sometimes conduct special blood tests or scans to determine the cause.

How do you measure temperature?

It is not recommended to measure your child or baby’s temperature routinely unless you are worried that they might have a temperature. If your child feels hot to touch, or there is something about their behaviour that doesn’t seem normal, such as them crying a lot or seeming miserable, it can be worth checking their temperature. Importantly, children who feel hot to touch do not always have a temperature and how hot they feel does not always correspond with how high their temperature is. This is because the temperature that matters is the core body temperature, which is different to the skin temperature, so it is important to get a thermometer to check the number.

What thermometer should you use?

The recommended ways of measuring temperature depend on the age of your child:

  • Babies under the age of 4 weeks:
    • Electronic thermometer in the armpit
  • Children 4 weeks to 5 years:
    • Electronic thermometer in the armpit
    • Chemical dot thermometer in the armpit
    • Infra-red thermometer in the ear

Digital armpit thermometers are the most accurate, easiest to use properly and can be used right from birth. Other types of thermometers not listed above are not recommended as they are not reliable or safe. These include any forehead based skin strips or thermometers in the mouth or bottom.

How do you measure a temperature with these?

  • Electronic armpit thermometer:
    • Hold your baby comfortably in your lap and place the tip of the thermometer in their armpit
    • Gently but firmly hold their arm against their body in order to hold the thermometer in the same place. Most digital thermometers will beep when they are ready, but for some you will need to count the seconds and check the instructions to see how long to hold it for.
    • The display will then show the temperature
  • Infra-red ear thermometer:
    • Hold your baby comfortably in your lap with their head gently held still
    • Lightly pull the top of the ear up and back and then insert the tip of the thermometer into the ear so that it is sealed around the outside edge
    • Press the button down as per instructions, the thermometer will usually beep when ready
    • The display will then show the temperature

Sometimes a reading can be falsely high if your child is wrapped up tightly in a blanket or in lots of clothes, has had a hot bath or been very active. If this happens, let your child cool down for a few minutes and take the temperature again to see if there is any change.

You can read Dr Sarah Montgomery-Taylor’s article on managing your child’s fever here

Main Points

  • High temperature in children is common.
  • Most temperatures in children are not serious and can safely be managed by parents at home.
  • Temperatures occur as a normal part of the body’s immune response to an infection.
  • Other situations that can cause temperatures in children include having routine immunisations. The health professional giving them the vaccination should warn you if this is the case.
  • The main groups of bugs which cause infection are viruses and bacteria. Viruses are more common in children than bacterial and other infections.
  • There are a few common misconceptions regarding infections in babies and children, and there tends to be confusion around the difference between viruses and bacterial infections.
  • It is not recommended to measure your child or baby’s temperature routinely unless you are worried that they might have a temperature.
  • Remember that children who feel hot to touch do not always have a temperature and how hot they feel does not always correspond with how high their temperature is. This is because body temperature is different from skin temperature.
  • The recommended ways of measuring temperature depend on the age of your child.
  • Digital armpit thermometers are the most accurate, easiest to use properly and can be used right from birth.
  • To use a digital armpit thermometer, hold your baby comfortably in your lap and place the tip of the thermometer in their armpit.
  • If your child is wrapped up tightly in a blanket or in lots of clothes, has had a hot bath or been very active, this may affect the reading. You should let them cool down for a few minutes and then take their temperature again.

References

Fever in under 5s: assessment and initial management https://www.nice.org.uk/guidance/cg160