How to Take a Baby’s Temperature: Armpit, Ear or Forehead by Age

For a baby under 3 months, use a digital thermometer in the armpit, every time. From about 3 months a forehead thermometer is fine for a quick check, an ear thermometer from about 6 months, and under the tongue only once a child can keep their mouth closed round it, usually at 4 to 5 years. This guide covers the method for each age, the mistakes that give false numbers, and the few readings that mean a doctor today.

Which thermometer is best for a baby, by age

A thermometer is only as good as the place you put it. Each type has an age where it gets accurate, and an age where it doesn’t.

Why no ear reading in young babies? Their ear canal is tiny and curved, so the probe often “sees” the wall of the canal instead of the eardrum. The number comes out low. Forehead guns are quick and a sleeping child doesn’t wake, but they read the skin, and skin is easily fooled by sweat, a fan, a hat or a cold room. Treat it as a screen. If it says fever, confirm it in the armpit.

Once you have a number, the house guide to bachon ka bukhar by age explains what it means for your child’s age band.

How to check fever with a digital thermometer in the armpit

This is the method that works from birth to adulthood. It takes under a minute on most digital sticks, costs less than a box of nappies, and gives a number you can read out to a doctor on the phone without any guesswork about which kind of thermometer or which part of the body you used.

1. Wipe the tip with a cotton pad and a little rubbing alcohol, or soap and cool water. Let it dry.
2. Wait 15 to 20 minutes if the baby has just had a bath, been wrapped tight in a shawl, or come in from the sun.
3. Take off the vest on that side so the tip touches bare skin. Dry the armpit with a soft cloth; sweat cools the skin.
4. Put the tip right into the centre of the armpit, pointing up towards the head.
5. Bring the arm down against the side and hold the elbow gently across the chest. For a baby, cuddle them on your lap facing you.
6. Keep still until it beeps, usually 10 to 60 seconds. If there’s no beep after 2 minutes, the battery may be low.
7. Read it, then write down the number, the time and “armpit”. Clean the tip again.

One small fact that surprises parents: on most digital sticks the beep means “the number has stopped rising”, not “finished”. If you took it out early and it read 36.2 °C, try again and hold longer.

Holding a wriggling toddler

Sit them sideways on your lap with the thermometer arm against your body. Your arm goes round them and holds their elbow down. A phone video, a song, or a sibling holding a toy works better than a struggle. A crying, hot, overdressed child reads a little higher, so settle them first if you can.

Forehead and ear thermometer: how to get a fair number

Forehead (infrared, no-touch)

Keep the thermometer and the child in the same room for 10 minutes before using it. Wipe away sweat, push the hair back, and hold it at the distance the box says (often 1 to 3 cm). Scan the centre of the forehead. Take two readings a minute apart. If they differ by more than about 0.3 °C, one of them is wrong; use the armpit instead.

Ear (from about 6 months)

Use a fresh probe cover if your model takes them. Gently pull the outer ear back (for older children, back and a little up) to straighten the canal, then push the tip in snugly and press. Wax and an ear that has been lying on a pillow can both shift the number, so use the same ear each time.

Normal temperature and fever: the numbers that matter

A child’s normal temperature sits roughly between 36.5 and 37.5 °C, and it’s a little higher in the evening. Most doctors call 38 °C or more a fever, whichever site you used. The site still matters, because the armpit runs cooler than the ear or forehead.

• Armpit 37.5 °C: warm, worth rechecking in 30 minutes. Not the same as 38 °C in the ear.
• Anything 38 °C or more: fever.
• Under 3 months, 38 °C or more: same-day doctor, even if the baby seems fine.
• 3 to 6 months, 39 °C or more: doctor today.
• Any age: fever over 3 days, or 39 °C or more with the child unwell, needs a doctor.

Should you add half a degree to an armpit reading? Many families do, and some old charts say so. It’s better not to. Here’s why. Tell the doctor the raw number and the site (“37.8 in the armpit at 9 pm”). They know how to read it, and you avoid adding twice.

How the child looks matters more than the number. Every time. A 38.5 °C child who is playing and drinking is less worrying than a 37.8 °C baby who is floppy and won’t feed. For what to do once you have a fever (fluids, clothing, sponging and when medicine helps), see fever care at home; it isn’t repeated here.

Myth: you can feel a fever with the back of your hand

The hand on the forehead is the oldest thermometer in any house, and it does pick up a big fever. It misses the in-between ones, and it’s badly fooled when your own hands are cold from washing up or hot from the tawa. It also can’t tell a 38 °C baby from a 38.5 °C one, and in a newborn that difference decides whether you go in tonight. Use your hand to decide to measure. Then measure.

A second myth: that a teething baby runs a real fever. Teething can make a baby a little warm and grumpy, but 38 °C or more is a fever with another cause and should be treated as one.

Mercury thermometers, strips and phone apps

The glass mercury thermometer many of us grew up with does work, but it can snap in a biting mouth or a dropped hand, and the mercury vapour is harmful to small children. Keep it out of the child’s reach, and if you still own one, replace it with a digital stick, which costs about the same as a meal out.

Plastic forehead strips that change colour are too rough to trust for a baby. Phone apps that claim to read temperature through the camera or screen can’t do it. Rectal readings are the most accurate and are used in hospitals, but at home they carry a risk of injury and should only be done if a doctor has shown you how.

More child-health guides live in Bachon Ki Sehat.

Questions parents ask about thermometers