If you think your baby has a fever it's important to know exactly what his temperature is, so you'll need a good digital thermometer.

Regular multi-use digital thermometers are sold in drugstores and relatively cheap. They're easy to use, easy to read, and fast  giving a reading in 10 seconds to two minutes. Most can be used rectally, orally, or under the arm, although taking your child's temperature orally won't be an option until he's at least 4 years old. If you have a multi-use thermometer, designate it for just one area to avoid spreading bacteria.

Taking your baby's temperature rectally will give you the most accurate result, and the best tools for this are rectal thermometers, which are designed specifically for this purpose. Look for one with a flexible tip and a wide handle that won't let you insert the thermometer more than an inch. Inserting it farther can perforate your child's rectum.

More expensive options include temporal artery thermometers, which use an infrared scanner to measure a baby's temperature with a simple swipe across the forehead, and tympanic (ear) thermometers, which can be trickier to use. Other temperature-taking tools, such as pacifier thermometers and temperature-sensitive strips that you place on a child's forehead, are too inaccurate to be useful.

Whichever method you choose, don't take your child's temperature right after a bath, when his body temperature is likely to be temporarily elevated. Wait at least 20 minutes after bath time for an accurate reading. The same is true if your baby's been swaddled.

Different thermometer types: pros and cons

Mercury/alcohol thermometer: The traditional thermometer makes use of mercury or colored alcohol hermetically sealed inside a glass tube. When inserted under the tongue, in the armpit or inside the rectum, the heat from the body causes the mercury or alcohol to expand and rise up the graduated tube.  The advantages of these types of thermometers is that they are cheap, easy to read, can be submerged in liquids, require very little maintenance and are reliable. The disadvantages are that they break easily and there is risk of mercury poisoning if the glass tube breaks. For those safety issues it has been not use recently as much as it used to be.

Digital thermometer: It uses electronic heat sensors and displays the reading digitally on a small LCD screen located on one side of its broader end. Just like the mercury/alcohol thermometer, it is inserted under the tongue or in the armpit or inside the rectum to measure body temperature. The advantages of digital thermometers are that they are inexpensive, easy to read, require very little maintenance and give an accurate reading. The disadvantage is that they get damaged easily if dropped and the battery powering them eventually runs out.

Tympanic thermometer: This is a type of digital thermometer that is used to measure body temperature by inserting it into the ear. Also called an ear thermometer its advantage is that it can obtain the temperature of a patient within two seconds without causing pain.

Temporal Artery thermometer:  Also called forehead tape thermometer, it is a use-and-throw out digital thermometer for single use. The tape thermometer has a mild adhesive on one side that allows it to be taped to the forehead. It is a handy thermometer that can be taken anywhere. However, its use has been mostly discontinued because of inaccurate readings and also because of the difficulty to keep it stuck to the forehead.

Infrared thermometer: This type of thermometer uses infrared technology to measure body temperature accurately and quickly.  Its advantage is that the temperature of a patient can be obtained within just one second.

Most physicians recommend digital thermometers for use both at home and by medical professionals.

The best way to take your tiny baby's temperature

It's best to use a digital thermometer under your baby's arm to take her temperature. Using a digital thermometer will quickly give you an accurate reading, and help you decide whether your baby had a fever or not.

When a temperature can be misleading

Your temperature doesn’t stay same all day, and it will vary throughout your lifetime, too. Some things that cause your temperature to move around during the day include:

  • activity, time of day, age, 
  • Infants and children temperature could be falsely high due to over dressing and/or extra swaddling on the other hand under dressing or exposure to cold environment. Other factors include drugs, or faulty thermometer as well as faulty method of measurement. 

Wondering if you should worry about your baby's high temperature? Find out when you should seek professional help here.