Fevers – a high temperature of at least 38C – are notoriously unpredictable and can go up and down over a few days or even longer.
While a fever is the body’s natural reaction to fighting off an infection, it can be worrying if your little one has a high temperature for a number of days, so we’ve got advice from a GP, and tips from parents.
How long can a fever last?
It’s completely normal for a fever to last around 3 or 4 days, but a high temperature can also be over quickly or take even longer to subside.
As a fever is the body’s natural response to fighting infections like coughs and colds, and other childhood illnesses like chickenpox, that high temperature is a good sign that your baby’s system is working hard to make them better.
MFM’s favourite GP Dr Philippa Kaye explains: “A fever is a temperature over 38C and is the body’s response to an infection. The infection itself doesn’t cause the fever, rather the body’s immune system causes it as it tries to fight the bug.
“As the fever is the body’s immune system fighting an infection and this takes a few days, often the fever can go up and down over a few days.
“The length of the fever is very variable, but they tend to only last a few days with the coughs, colds, sore throats, ear aches and diarrhoea and vomiting illnesses common in childhood.”
Writing on our forum, mum Allyd28 says her little one often has short-lived high temperatures: “J gets random high temperatures quite often. Will last 24 hours or so then he’ll be back to normal. I only medicate if it’s particularly high – over 38.5C normally.”
How do I know if my baby has a fever?
When your baby has a fever, you might spot tell-tale signs like red, flushed cheeks, or that they feel sweaty, or hotter than usual when you touch their forehead, back or tummy.
But you will only know for sure if they have a fever by checking with an accurate and reliable thermometer.
The NHS classes any temperature of 38C or higher as a fever in all babies and children up to 5 years old.
What does it mean if my baby has a fever for a few days, or longer?
There’s no need to panic if your baby has a fever for a few days, as it generally means their body is fighting off an infection, which could range from a common cough or cold, to an illness like chicken pox, Norovirus, tonsillitis, or an ear infection.
Your baby might also get a high temperature after injections, or when they are teething, so her first year might seem like it’s one fever after another.
Mum Simone’s little girl had a fever with teething, but luckily it was over quickly: “Jessica had a really high temperature when she was teething, but it was only for a day!”
“Having a short high fever or a slightly longer but lower one does not signify anything about the infection itself,” says Dr Philippa.
She points out that if your baby seems unwell, out of sorts and is not interested in food or producing wet nappies, this is the time to treat it: “If your child is unwell and you think they may have a fever then take the temperature and treat as appropriate.”
My baby has had a fever for 5 days – what should I do?
If your baby has a high temperature that has lasted for more than 5 days, then get an urgent GP appointment, says Dr Philippa.
It’s very unlikely to be something serious, but your doctor can have a good look at your child and advise you on the best action.
It’s worth looking out for other symptoms alongside a high temperature, such as any rashes, no interest in food and signs of dehydration like sunken eyes, no tears, or nappies that aren’t very wet.
What if my baby is really young with a fever?
Waiting 5 days to see a doctor is not a hard and fast rule with a fever, as a high temperature will need medical attention if your little one is tiny, or the fever is particularly high.
If your baby is less than 3 months old and has a temperature of 38C (101F) or higher, or if your baby is 3 to 6 months old with a temperature of 39C (102F) or higher then it’s time to get medical advice.
First port of call is your GP, but if it’s a weekend or the practice is closed, call NHS 111 or contact your local GP out-of-hours service.
It’s very rare that a fever could be a serious illness but, as Dr Philippa points out: “If you are concerned about your child please seek medical advice.”
Why is my baby’s temperature going up and down?
It might seem odd that your baby’s temperature is going up and down, but it can be due to any medicine wearing off.
“Medicines such as paracetamol and ibuprofen are relatively short acting,” explains Dr Philippa.
“You give paracetamol every 4-6hrs up to a maximum 4 times in 24hrs and ibuprofen every 6-8 hours up to a maximum 3 times in 24 hours, so it is common that the fever comes down while the medication is working and then goes back up as the medication wears off.”
Mum Allyd28 found that happening with her 21-month-old son: “J has had a high temp for 72 hours now. He was seen at [the] out-of-hours [clinic] on Tuesday night and GP thinks it’s viral. Calpol/Nurofen perk him up but as soon as they wear off his temp is up at 40.5.”
Meanwhile, spikeygoodness also found her little one’s temperature went up and down as the medicine wore off: “J (20 months) has an ear infection (probably, the hospital didn’t seem 100% certain) and has been on antibiotics since Monday night.
“He’s still spiking a fever of 40 degrees any time the Calpol/calprofen that we’re layering wears off.”
Babies of 2-3 months can be given infant paracetamol (like Calpol), but should be given a maximum of 2 doses, at least 4 hours apart.
What should I do if my baby’s temperature goes up at night?
You should check your baby regularly through the night, as a high temperature can be uncomfortable and affect their sleep.
It’s common for your baby’s temperature to rise at night, as any medication wears off, says Dr Philippa.
Offer her regular drinks or breastfeed to keep her hydrated, and don’t overdress her.
How can I make sure I get an accurate temperature reading?
A reliable thermometer is an essential bit of parenting kit but remember forehead thermometers shouldn’t be used, as they can give inaccurate results, says the NHS.
In babies under 4 weeks, the best way to measure temperature accurately is with an electronic thermometer in their armpit, according to latest clinical guidelines from the National Institute for Health and Care Excellence (NICE).
From 4 weeks to 5 years, you can use electronic thermometers for the armpit, ear thermometers, and even no-contact infrared skin thermometers, that can be used without waking your baby.
What should I do if my baby’s fever gets better, then comes back?
“Sometimes a baby gets a fever for a few days and then seems to get better but then develops a fever again,” says Dr Philippa.
“Sometimes this means that there is a secondary infection, for example a cold and then an ear infection develops.
“If you think that your child has improved and then a fever recurs then treat with medicine such as baby paracetamol if appropriate and as always seek medical advice if you are concerned.”