Why is the thermometer kept under the tongue?

The thermometer is commonly kept under the tongue when measuring body temperature because the area underneath the tongue is rich in blood vessels and is relatively close to the body's core temperature. This method is known as the "oral" or "sublingual" method of temperature measurement.

The temperature of the blood flowing through these blood vessels closely reflects the core body temperature, which is the temperature of the internal organs. Placing the thermometer under the tongue allows for an accurate measurement of core body temperature without the influence of external factors like ambient temperature.

It's important to note that for accurate measurements using this method, the individual should not have consumed hot or cold beverages, smoked, or engaged in any other activity that could temporarily alter their oral temperature. Additionally, the thermometer should be kept in place for the recommended amount of time as per the manufacturer's instructions to ensure an accurate reading.