Taking a child's temperature

Photo of a woman taking her daughter’s temperature (PantherMedia / photodeti)

There are several different ways to take a child's temperature – for instance in their bottom (rectally), under their arm or in their ear. The most suitable approach will depend on the child's age and preferences.

Children are considered to have a fever if they have a body temperature of 38.5°C (101.3°F) or more, and babies under three months old are already considered to have a fever at a body temperature of 38.0°C (100.4°F) or more. The only way to reliably measure your body temperature is using a thermometer.

When measuring a young child's temperature, it's particularly important that it can be done quickly and with as little effort (such as undressing and dressing, or keeping still) as possible. The length of time needed to take the temperature depends on where it is measured and what kind of thermometer is used.

How can I tell if my child has a fever?

You can often tell that a child has a fever just by looking at them: Typical signs include a hot, red face, tired or glazed eyes and otherwise pale skin. Many parents who suspect that their child has a fever first place their hand on the child’s forehead. If the child’s forehead or neck feels hot, it could be a sign of fever. Many children lose their appetite or cry a lot. Some are very thirsty too.

What are the different types of thermometer and how accurate are their readings?

Battery-operated digital thermometers (contact thermometers) can measure a child's temperature in the bottom (rectally), in the mouth (orally, under the tongue) or under the arm. Infrared and chemical thermometers can be used to measure the temperature in their ear or on their forehead. They are more expensive than digital thermometers. In order to get accurate readings, it's important to use thermometers properly, following the instructions.

You can get the most accurate readings by measuring the temperature in the bottom or – in children aged four and over – in the mouth. But under the arm, in the ear or on the forehead is more pleasant for the child. In order to take a child's temperature properly in their mouth or under their arm, they have to be able to cooperate.

You can also combine two different approaches: If an ear or forehead thermometer reading shows that the child has a high temperature, you can check by taking their temperature in their bottom too.

Taking a child's temperature rectally

Measuring a child's temperature in their bottom gives accurate results but can be unpleasant for them. Before gently inserting the thermometer into the anus, it's best to put a bit of fatty cream on it first, so it can slide in better and doesn’t hurt.

You only need to insert the tip of the thermometer (1 to 2 cm deep) – the readings will still be reliable. Babies are usually laid on their back with their legs held high. Older children often prefer to lie on their stomach.

It is important to clean your hands and the thermometer thoroughly after taking the temperature, to avoid spreading any germs from the anus.

Taking the temperature in the mouth

When taking a child's temperature in their mouth, you first clean the thermometer. The tip of the thermometer is then placed under the tongue, toward the back. This approach provides very accurate readings. But the child has to cooperate by keeping their mouth closed and their tongue still while measuring. This can be difficult for young children.

The temperature taken won't be accurate if the child has had a hot or cold drink shortly beforehand.

Taking the temperature under the arm

When taking a child's temperature under their arm, the thermometer is placed under the armpit, and the child keeps their arm close to their body. Although this is a simple and convenient way to measure a child's temperature, the readings may be wrong if the child moves too much – up to 2°C (3.6°F) higher or lower than their actual body temperature. On average, temperatures measured in the armpit are about 0.5°C (0.9°F) too low.

Ear thermometer

Special infrared thermometers can be inserted into children's ears to measure the heat given off by their eardrum. Although ear thermometers provide fast results, they are much more expensive than digital thermometers.

For the measurement to be accurate, the sensor has to point toward the eardrum. This is easier if the child's ear is gently pulled up and back. Temperatures measured in this way are about 0.3°C (0.5°F) lower than the actual body temperature.

It's not all that easy to find the right place in the ear if you haven't had much practice, especially when taking a baby's temperature. The user manual describes how to use the ear thermometer correctly. You can test how accurate your ear thermometer readings are by taking a few measurements in the ear as well as rectally. If the readings are similar – i.e. only vary by about 0.3 or 0.5°C (0.5 or 0.9°F) – you can assume that the ear thermometer is just as accurate.

Forehead thermometer

Forehead or temple thermometers are easy to use, comfortable for the child and also work when he or she is asleep. They are available in various forms, including infrared thermometers, liquid crystal thermometers and chemical thermometers.

But they're less accurate than other approaches because the readings can be influenced by things like sweat on the skin. So forehead thermometers are currently not recommended if you need an accurate measurement.