What causes a fever in babies and toddlers?

A fever can be a common symptom of infections and childhood illnesses. Find out what causes fever in babies and toddlers with guidance from Dr Philippa Kaye

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A fever – a high temperature of at least 38C – is often a red flag that your baby or toddler has an infection or illness.

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While it’s the body’s natural response to fighting off common illnesses like coughs, colds, and chicken pox, it can very rarely be a sign of something more serious.

So we share the latest medical guidance on what causes a fever in babies and toddlers, and tips from a GP.

What are the main reasons babies get a fever?

A fever is very common in babies and young children and, while it isn’t an illness itself, it’s a good indicator your little one might be coming down with something.

Many things can cause a high temperature in children, from common childhood illnesses like coughs, colds, chickenpox and tonsillitis, to vaccinations and teething.

These can all be uncomfortable and painful at times, but generally can be treated at home or with a trip to the GP.

Research has shown that a raised temperature is the body’s way of fighting an infection, as it helps the immune system get to work against the illness.

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MFM’s GP Dr Philippa Kaye explains: “A fever is part of the body’s defence system against infection – to heat the body up in an attempt to kill off whatever bacteria or virus is causing the infection.

“The virus or bacteria doesn’t cause the fever, your immune system does, but releasing chemicals called pyrogens into your blood which act on the hypothalamus in the brain which controls body temperature.

“So, a fever can be a useful thing, which is why unless your child is unwell, miserable and not drinking you don’t always need to treat a fever. If they are running around as normal, leave it be.”

Read more on what temperature is a fever in babies and toddlers, and when to call a doctor

Fever with a cold

There’s a reason they call it the common cold: babies can get up to 8 colds in the first year alone, mainly because their immune systems are still developing.

Colds are infections of the upper respiratory tract, which includes the nose, throat and sinuses, and can be caused by numerous different viruses.

And if your baby has a cold, along with the bunged-up, runny nose, it’s likely she’ll have a fever too.

“Children can have a fever with coughs and colds, tummy bugs causing diarrhoea and vomiting, ear infections, sore throats and more,” explains Dr Philippa.

And while colds are usually not serious, it’s important to take your child to be checked out by a doctor if they are under 3 months with a fever of 38C or between 3-6 months with a fever of 39C.

If the fever lasts for 5 days or more, or your baby isn’t drinking, it’s also time to get a GP appointment.

Fever with an ear infection

An ear infection can be especially distressing, as the illness can come on quickly and be very painful.

If your baby has a fever along with tell-tale signs like pulling their ear, or if the ear is red or inflamed, there’s a good chance she could have an ear infection.

“The fever is not a specific response to a specific infection, rather the response of the immune system to the presence of an infection,” points out Dr Philippa.

Other signs your baby might have an ear infection include irritability or restlessness, not reacting to some sounds, losing balance or being off their food.

And while most ear infections clear up after a few days, the symptoms could last for up to a week in some cases.

Writing on our forum, mum Quesera was concerned about her son’s high temperature and general illness, as well as not wanting to drink.

Taking him to the doctor helped get to the bottom of what was causing the fever: “My poor little man. I couldn’t keep his temperature down and he has just been sleeping all day, so I took him to the doctor and he has got tonsillitis and an ear infection,” she said.

Fever with diarrhoea

If your baby has a fever with diarrhoea it could be a number of things: teething (if it’s accompanied by red cheeks and sore gums) or some kind of gastric infection or stomach bug.

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Norovirus – also called the winter vomiting bug – causes diarrhoea and vomiting with a fever and can be really nasty for a few days, with a plentiful supply of nappies and changes of clothes a must!

Food poisoning is another cause of diarrhoea and vomiting with a fever, and can also cause stomach cramps, aches and pains and feeling really unwell and run down.

If your little one has a fever with diarrhoea caused by norovirus, food poisoning or some other stomach bug, it’s best to keep her at home for a few days so she doesn’t pass on the infection.

Mum Lauren29, writing on our forum, experienced the pain of one illness after another, when her baby got an ear infection followed by the norovirus.

“My poor J has struggled with an ongoing ear infection for weeks. He has just started to get rid of it and feel much better and has since last night…. [but has] now got Norovirus!!” she wrote. “He’s got a temperature and is so upset this morning…poor thing!”

The NHS recommends taking your baby or toddler to the GP with diarrhoea if they:

  • are under 12 months old and have signs of dehydration – such as fewer wet nappies
  • are under 3 months old and have a temperature of 38C or higher
  • are 3 to 6 months old and have a temperature of 39C or higher
  • have diarrhoea for more than 7 days
  • have vomiting for more than 2 days.

My baby has a fever with spots or a rash – what should I do?

If your baby has a high temperature with spots or a rash, this again could mean she has one of any number of illnesses, usually not serious – but that might need treating professionally.

These might include chicken pox, slapped cheek syndrome, roseola, or hand, foot and mouth disease, all of which are likely to cause a fever.

Illnesses like measles and rubella – which are fairly rare now because of widespread vaccination – can also cause a fever with a rash or spots.

For mum Lucy-H, writing on our forum, her son was unlucky enough to get chicken pox twice (yes, it is possible!) and suffered with a fever both times.

“Aaron has got chickenpox again. He had it when he was 5 1/2 months old and it was really bad. He was covered from head to toe and felt poorly with a temperature,” she said.

“And now he has it again, the spots so far are not too bad but he was feeling poorly and had a temp over 39C. With the help of [medicine] he is feeling brighter and his temperature has come down.”

However, there are some much more serious illnesses which can cause a rash or spots and a fever, such as meningitis or septicaemia, so it’s always good to be alert and seek medical advice if you are worried.

A quick check can be done with a glass, and Dr Philippa explains this is an easy test to do at home.

“Check if the rash blanches – or fades – when a glass is pressed against it,” she says.

“If it doesn’t call 999 as this could be a sign of a serious infection (such as meningitis) causing septicaemia.

“If it does blanche see your GP, as many infections cause rashes and some of them are diagnostic of the virus causing them such as the rash of chickenpox, but many cough and cold viruses will also cause a very fine blanching rash, often on the trunk of the body.”

Check out our picture guide to children’s rashes and spots

When is a fever a sign it could be a serious illness?

The vast majority of the time, a baby or toddler’s fever will be caused by an everyday childhood illness, teething or a vaccination, which can be treated by regular monitoring and liquid paracetamol or ibuprofen if needed.

But very occasionally a fever can be a sign of a more severe illness if the high temperature comes with other worrying signs and symptoms.

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“A fever can be a sign of a serious illness such as meningitis but this is accompanied by other symptoms you need to look out for,” advises Dr Philippa.

“It could be a serious illness if your child has a fever which you can’t control with medications, has a stiff neck, has a rash which doesn’t blanche (fade) under a glass, is lethargic or you can’t rouse them, or has cold hands and feet.”

In that case, it’s wise to call 999 and seek immediate medical help, she says.

Should I be worried if my baby is very young with a fever?

You will need to pay a visit to the doctor if your child is under 3 months old and has a fever higher than 38C, or is between 3-6 months old and has a fever over 39C.

Dr Philippa adds that any child with a fever for more than 5 days, or who isn’t drinking, should see a doctor. “If you are concerned please do see your GP,” she advises.

What should I do if my baby has a fever from an illness?

Monitoring your baby’s temperature is a great idea, as it can be reassuring to keep tabs on the fever. And the good news is there are lots of thermometers out there.

Take a look at our pick of the best baby thermometers

While your little one does have a fever, keep an eye out for any signs of dehydration like fewer wet nappies or a dry mouth.

“You can use paracetamol or ibuprofen but also give plenty of fluids – a breastfed baby may need or want to feed more often,” says Dr Philippa.

It’s important not to give paracetamol (like Calpol) to babies under 2 months, and not to give ibuprofen (like Nurofen) to babies under 3 months or 5kg, or to those with asthma.

And, as ever, if you are at all worried, see your GP.

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