What temperature is a fever in a baby? What to do and when to ring the GP
The number that counts as a fever, how to measure it properly and the short list of signs that mean ring someone now.
In short
A normal baby temperature is around 36.4°C. A fever is 38°C or higher. A baby under 3 months with 38°C or higher, or under 6 months with 39°C or higher, needs to be seen by a doctor the same day.
- Measure under the arm with a digital thermometer. Ear thermometers are less accurate in small babies. Never use a forehead strip or a mouth thermometer.
- Ring 999 or 112 for breathing trouble, blue lips, a floppy or hard-to-wake baby, a fit, a rash that does not fade under a glass or a high-pitched or weak cry.
- Keep the baby cool with light clothing and a normal room. Do not sponge with cold water. Offer extra feeds.
- A mild, short fever after vaccines is common. Teething does not cause a true fever.
- Write each reading down with the time so the GP gets a clear picture.
A fever in a baby is a temperature of 38°C or higher. Normal is around 36.4°C, and a baby under 3 months with 38°C or higher needs to be seen by a doctor the same day.
That is the whole answer for most 3am searches. The rest of this guide covers how to measure it properly, which numbers mean a phone call, which signs mean 999 and how to keep a warm baby comfortable while you wait.
What temperature is a fever in a baby?
A normal temperature for a baby is around 36.4°C, and it drifts a little either side of that through the day. A fever is 38°C or higher. So a reading of 37.2°C or 37.6°C is a warm baby worth keeping an eye on, not yet a fever.
A fever is not an illness on its own. It is the body's normal response to an infection, and most of the time the infection is a cold or another minor virus. What matters far more than the exact number is how old your baby is and how they look and behave, which is why the next few sections are about age limits and warning signs rather than decimal points.
How do I take my baby's temperature?
For a baby under 5, the HSE advice is to measure under the arm with a digital thermometer. Here is how:
- Sit the baby on your knee or lie them down and put the tip of the thermometer in the armpit.
- Hold the arm gently against the body so the tip is fully covered.
- Wait for the beep, or as long as the instructions say, then read the number.
A few things to avoid. Ear thermometers are less accurate in small babies because the ear canal is so narrow. Forehead strips measure the skin, not the baby, and are not reliable. Never put a thermometer in a baby's mouth. If you only have an ear thermometer and it says 38°C or higher, treat that as a fever and check again under the arm if you can.
Take the temperature when the baby has been indoors and settled for a few minutes. A baby straight out of a warm car seat or a long cry can read high for a moment and then settle.
What temperature should I take my baby to the doctor?
This is where age matters more than anything else. Young babies cannot fight infections the way older children can, so the threshold for getting them seen is lower.
| Baby's age | Temperature | What to do |
|---|---|---|
| Under 3 months | 38°C or higher | Seen by a doctor the same day |
| 3 to 6 months | 39°C or higher | Seen by a doctor the same day |
| Any age | Any fever with the 999 signs below | Ring 999 or 112 |
"Seen the same day" means ring your GP during the day. Out of hours, ring the out-of-hours GP service for your area, such as SouthDoc in Cork and Kerry, or go to the emergency department. Do not wait until the morning with a baby under 3 months who has a temperature of 38°C or higher, even if they seem fine in themselves.
For an older baby with a fever below those limits, use your judgement. A baby who is drinking, has wet nappies, is settling between grumpy spells and is mostly themselves can usually be watched at home. A baby who is getting worse, has had a fever for more than a couple of days, or just seems wrong to you should be seen. Parents are good at spotting "not right", so trust that.
When should I call 999 for a baby?
Ring 999 or 112 straight away if your baby:
- Is struggling to breathe, breathing very fast, grunting or sucking in under the ribs
- Has blue lips or a blue tinge to the skin or tongue
- Is floppy, unusually limp or hard to wake
- Has a fit or seizure
- Has a rash that does not fade when you press a glass against it
- Has a high-pitched or weak cry that is not their normal cry
Any one of these is enough. You do not need to tick several boxes, and you do not need to take the temperature first. Ring, then keep the baby with you until help arrives.
How do I bring a baby's temperature down?
The goal is a comfortable baby, not a perfect number. A mild fever is doing a job, and you do not need to chase it back to 36.4°C. What helps:
- Light clothing. A vest or a light babygro, and a light blanket if they need one. Take off the extra layers you added because they felt warm.
- A normal room temperature. Around 16 to 20°C is fine. Do not turn the heating up, and do not open every window to make it cold either.
- Do not sponge with cold water or put them in a cool bath. It makes the baby shiver, which pushes the temperature up, and it is upsetting for everyone.
- Offer extra feeds. Breast or bottle, little and often. A warm baby loses more fluid, and the thing you are guarding against is dehydration.
- Watch the nappies. Aim for 6 or more wet nappies in 24 hours. Fewer than that, or dark urine, is a reason to ring the GP.
On medicines: ask your pharmacist, PHN or GP about medicines for babies and follow the pack for the baby's weight and age. Very young babies need advice before anything is given, so if your baby is under 3 months, ring first.
Is it normal for a baby to have a temperature after vaccines?
Yes. A mild, short fever after a vaccine is common, especially after the 2, 4 and 6 month visits, and it usually settles within a day or two. Your baby may also be grizzly, sleepy or off their feeds a little, and the leg where the injection went in can be red or sore. All of that is the immune system doing what the vaccine asked it to do.
The age rules still apply, though. A baby under 3 months with a temperature of 38°C or higher after their 2 month jabs should still be seen the same day, because a doctor cannot tell from the number alone whether it is the vaccine or something else. Your PHN or GP will usually tell you at the appointment what to expect afterwards and when to ring. Our guide to the Irish vaccine schedule covers what to expect after each visit.
Can teething cause a fever?
No. This is one of the most repeated myths in parenting. Teething can make a baby a bit warmer, drooly, crankier and keen to chew on everything, but it does not cause a true fever of 38°C or higher. If a teething baby has a fever, something else is going on, usually a cold or another common virus, and it should be treated as a fever with the same age rules above.
The reason this matters is that "it's only teething" is how a real infection gets missed. Cutting a tooth and picking up a virus at the same time is very common at 6 to 12 months, because the two overlap for such a long stretch. Our teething guide goes through what teething does and does not do.
How do I keep track of a temperature overnight?
Write each reading down with the time, and beside it note the feeds and the wet nappies. By the time you are on the phone to the GP at 8am you will have been up half the night and will not remember whether the 38.4°C was at 1am or 3am, or how many feeds went in. A pad of paper by the bed does the job. Lullagram does the same thing on your phone: it logs temperature readings, feeds and nappies on one timeline that you can show the GP in the surgery or export as a report. It is free to try on Android, iPhone and web.
This is a guide, not medical advice. If you are worried about your baby, ring your PHN or GP.