How to Take a Newborn's Temperature

Read this part first

A temperature of 38C (100.4F) or higher in a baby under three months is a medical emergency, and so is one below 36C (96.8F). NICE's fever guideline NG143 states that children younger than three months with a temperature of 38C or higher are in a high-risk group for serious illness. NICE's postnatal care guideline NG194 lists a temperature of 38C or over, or under 36C, among its red flags for serious illness in young babies, and says a red flag means immediate assessment.

The NHS's own trigger is the same: ask for an urgent GP appointment or call 111 if your baby's temperature is 38C or higher and they are under three months, or 39C or higher at three to six months. The HSE gives identical numbers. Go straight to emergency services if a high temperature comes with a rash that does not fade when you roll a glass over it.

NICE adds one more thing that matters at this age: be aware that fever may not be present in young babies with a serious infection. A normal reading is not a clean bill of health.

Which thermometer

The NHS: "Ideally, you need a digital thermometer to get a fast, accurate reading." The HSE agrees: "The best way to check your child's temperature is with a digital thermometer. Ear or strip thermometers may not be as accurate."

The NHS's assessment of the alternatives:

• Ear (tympanic) thermometers — quick but expensive, and "they can give misleading readings if you do not put them in the ear correctly, which is more likely to happen with babies because their ear holes are so small".
• Strip-type thermometers held against the forehead — "not an accurate way of taking a temperature. They show the temperature of the skin, rather than the body."
• Mercury glass thermometers — never use one. The NHS says they can break, releasing glass splinters and highly poisonous mercury, and that they are no longer used in hospitals or sold in shops. Both the NHS and HSE say to get medical advice immediately if a child is exposed to mercury.

NICE's recommendations for professionals set the standard the rest follows:

• In infants under four weeks, measure body temperature with an electronic thermometer in the axilla — the armpit.
• From four weeks to five years, an electronic thermometer in the armpit, a chemical dot thermometer in the armpit, or an infra-red tympanic thermometer.
• Do not routinely use the oral or rectal routes in children aged 0 to 5.
• Forehead chemical thermometers are unreliable and should not be used by healthcare professionals.

How to do it

The HSE's method, which is the armpit technique NICE specifies:

• Lie your baby flat, or sit an older child comfortably on your knee.
• Put the thermometer in their armpit.
• Gently hold their arm against their side to keep the thermometer in place. Follow the instructions for how long — many digital thermometers beep when ready.
• Read the display.

Skin-to-skin contact between the thermometer tip and the armpit is what makes this accurate, so make sure no clothing is in the way and the arm stays down.

What can throw the reading off

The NHS lists the situations that alter a reading: your baby has been wrapped up tightly in a blanket, in a very warm room, very active, cuddling a hot water bottle, wearing a lot of clothes, or has just had a bath. Its advice is to let them cool down for a few minutes — without letting them get cold or shivery — then take the temperature again. The HSE says the same: do not take a temperature immediately after a bath or when your child is wrapped in warm clothing.

What counts as normal

The NHS: "A normal temperature in babies and children is about 36.4C, but this can vary slightly. A high temperature or fever is usually considered to be a temperature of 38C or above." The HSE gives a normal range of around 36.5C to 37.5C.

The NHS's signs that a baby may have a high temperature, and that it is worth checking: they feel hotter than usual on their back or chest, feel sweaty or clammy, or have flushed cheeks. The HSE adds being more irritable than usual. Note that both bodies say to feel the chest, back or forehead — hands and feet are normally cooler and tell you nothing.

Low readings

The HSE takes a sensible line: if your thermometer reads low, most of the time it is nothing to worry about, because accurate readings are hard to get on small babies. But it says to get urgent advice if a low body temperature comes with chills, breathing problems, shaking or trembling, or confusion. In a baby under three months, a reading below 36C is on NICE's red flag list, so repeat it and act on it rather than dismissing it.

About medicines

NICE gives two instructions that change how parents use a thermometer. First: do not use fever medicines with the sole aim of reducing body temperature. Second, and more important: when a child has been given an antipyretic, do not rely on whether the temperature comes down at one to two hours to tell serious illness from non-serious illness. A fever that responds to medicine has not been explained by responding.

There are age limits on infant medicines, and they are strict in the newborn period. Paracetamol may be an option for some babies, but only from a specific age and at an amount set by the packaging or a pharmacist — this page names no amounts. In a baby under three months, medicine is not the first move at all: assessment is.

When to call

Call your local emergency number (999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand) if your baby:

• Is under three months with a temperature of 38C (100.4F) or above, or below 36C (96.8F).
• Has a rash that does not fade when you press or roll a clear glass over it.
• Looks pale, ashen, mottled or blue, or is unresponsive or unrousable.
• Has a weak, abnormally high-pitched or continuous cry.
• Is grunting, breathing over 60 breaths a minute, or drawing their chest in.
• Has a bulging fontanelle, neck stiffness, or a seizure.

Get urgent advice from your GP, out-of-hours service or NHS 111 if your baby: is three to six months with a temperature of 39C or above; has a high temperature with other signs of illness; is feeding poorly or has fewer wet nappies; or is more irritable or sleepier than usual. NICE explicitly tells professionals that reported parental perception of a fever should be considered valid and taken seriously — so say it even if the number does not support you.

What to let go of

Forehead strips, smartphone attachments and the back of your hand. Buy a digital thermometer, use it in the armpit, and remember that the number is only half the picture — NICE's own warning is that a young baby with a serious infection may not have a fever at all.