How does a thermometer measure body temperature?

Jan 21, 2025 Source: Cainiu Health

Dr. Ren Yi

Introduction

Under normal circumstances, methods for measuring body temperature with a thermometer include axillary measurement, oral measurement, rectal measurement, post-auricular (behind the ear) measurement, and forehead temperature measurement. If body temperature rises, it is recommended to seek medical attention promptly and receive appropriate treatment under a doctor's guidance. It is advised to remain calm during measurement, avoid strenuous activity and emotional fluctuations, and conduct the measurement in a comfortable, quiet environment with suitable room temperature.

Generally, there are several methods for measuring body temperature with a thermometer, including axillary (under the armpit) measurement, oral (under the tongue) measurement, rectal (anus) measurement, behind-the-ear measurement, and forehead temperature measurement. If an elevated body temperature occurs, it is recommended to seek medical attention promptly and receive appropriate treatment under a doctor's guidance. Detailed explanations are as follows:

1. Axillary measurement: If using a mercury thermometer, first shake the mercury column down to below 35°C, then disinfect the thermometer with an alcohol swab. Wipe away sweat from the armpit and place the end containing the mercury column deep into the armpit. Bend the arm across the chest and hold the thermometer tightly in place. After 10 minutes, remove the thermometer and read the displayed scale.

2. Oral measurement: Oral measurement should be conducted at least half an hour after eating, drinking, or smoking. Place the mercury thermometer diagonally under the tongue. Ask the patient to keep their lips tightly closed without biting the thermometer with their teeth. After 3 minutes, remove the thermometer. When reading the temperature, hold the thermometer horizontally and slowly rotate it to view the temperature indicated by the mercury column.

3. Rectal measurement: For rectal measurement, first apply some oil-based lubricant to the rounded end of the rectal thermometer. Slowly insert the mercury thermometer into the anus 3–5 cm and hold the upper end with your hand. After 3 minutes, remove the thermometer.

4. Behind-the-ear measurement: If using an electronic thermometer, disinfect the probe end with alcohol before use. Press the power button and wait until the electronic thermometer displays "Lo°C," with the "°C" symbol flashing, indicating it is ready for measurement.

5. Forehead measurement: If using an infrared thermometer, adjust the temperature measurement mode to "temperature." Point the infrared sensor toward the forehead while keeping it perpendicular. It is recommended to maintain a distance of approximately 1–3 cm from the forehead. Aim at the measurement site and press the temperature button until the screen displays the temperature reading.

It is recommended to remain calm during measurement, avoid vigorous activity and emotional fluctuations, and refrain from taking measurements in drafty or cold environments. Measurements should be preferably conducted in a quiet and comfortable environment with suitable room temperature.

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How to Use an Electronic Thermometer Correctly

Under normal circumstances, the correct use of an electronic thermometer mainly includes cleaning and preparation, turning on and preheating, selecting the measurement site, proper placement and waiting, reading and recording the result. During the use of an electronic thermometer, follow the instructions provided in the user manual to ensure measurement accuracy and safety. Pay attention to keeping the measurement site dry and clean to improve measurement accuracy.

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How many days does a fever usually last with Type A flu?

Under normal circumstances, fever caused by influenza A usually lasts for 3–5 days; in children infected with influenza A, fever may persist for 5–7 days. If any discomfort occurs, seek immediate medical attention. Body temperature should be measured regularly, and it is recommended to use a mercury or electronic thermometer to measure axillary temperature. Generally, the temperature should be measured every 4–6 hours to accurately monitor temperature changes.

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What is the normal body temperature?

The normal temperature measured by a thermometer varies depending on the measurement site. If the thermometer is used under the armpit, the normal range is generally between 36.0°C and 37.0°C. If the thermometer is used in the mouth, the normal range is between 36.3°C and 37.3°C. If the thermometer is used rectally, the normal range is between 36.5°C and 37.7°C.

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Can bleach disinfect a thermometer?

Under normal circumstances, bleach is not recommended for disinfecting thermometers. Thermometers are precision medical devices, and their disinfection must follow specific guidelines and standards to ensure accuracy and safety. Bleach primarily contains sodium hypochlorite, which has strong oxidizing and corrosive properties. It is recommended to use specialized medical disinfectants or follow established disinfection protocols for medical devices.