Make sure his underarm area is dry, and then slip the bulb under his armpit. To get a reading, the bulb needs to be in full contact with the skin, so hold his arm firmly against his side or bent and folded across his chest. A digital thermometer will beep when it's ready, usually after one or two minutes. You'll need to keep a glass thermometer in place for at least three minutes. Don't use temperature-sensitive strips that you place on your baby's brow or under his arm.
Doctors say they're unreliable.
Hold off on using an oral thermometer until your child is about 7 or 8 years old, says pediatrician and BabyCenter advisor David Geller. Until then, he probably won't be able to safely hold a thermometer in his mouth or keep it under his tongue for the required time. Oral readings are virtually impossible to get from a squirming, crying baby or toddler, and they're generally 1 degree lower than rectal readings, anyway. It's probably best to hold off on using an ear thermometer until your baby is at least 3 months old. Because young infants have such narrow ear canals, ear thermometers may not be accurate.