Medical thermometers are devices that estimate body temperature, a key sign of health and illness. Fever can show that the immune system is responding to infection, while low temperature can signal dangerous heat loss or shock. Modern thermometers are designed to give fast, safe, and repeatable readings in clinics, homes, schools, and hospitals.
Digital, infrared forehead, and tympanic ear thermometers all measure temperature, but they sense heat in different ways.
Key Facts
- Body temperature is commonly reported in degrees Celsius or degrees Fahrenheit.
- Temperature conversion: F = 9C/5 + 32 and C = 5(F - 32)/9.
- A typical average core body temperature is about 37.0 C or 98.6 F, but normal values vary by person, time of day, and measurement site.
- Digital contact thermometers often use a thermistor, where electrical resistance changes with temperature.
- Infrared thermometers detect thermal radiation from the skin or eardrum and convert it to an estimated temperature.
- A fever is often considered 38.0 C or higher, but the medical meaning depends on age, symptoms, and measurement method.
Vocabulary
- Thermistor
- A temperature-sensitive resistor used in many digital thermometers to convert heat into an electrical signal.
- Infrared radiation
- Electromagnetic radiation emitted by warm objects that can be detected to estimate temperature without direct contact.
- Tympanic thermometer
- A thermometer that estimates body temperature by measuring infrared radiation from the eardrum area.
- Calibration
- The process of adjusting or checking a device so its readings match a known standard.
- Core body temperature
- The temperature of the body's internal tissues and organs, which is usually more stable than skin temperature.
Common Mistakes to Avoid
- Confusing skin temperature with core temperature is wrong because forehead skin can be cooled by sweat, wind, or room temperature and may not exactly match internal body temperature.
- Using a thermometer immediately after eating, drinking, bathing, or exercising is wrong because recent heating or cooling can temporarily change the reading site.
- Pointing an infrared forehead thermometer from the wrong distance is wrong because the sensor is calibrated for a specific measurement range and spot size.
- Treating all thermometer readings as interchangeable is wrong because oral, rectal, axillary, forehead, and ear measurements can differ systematically.
Practice Questions
- 1 A digital thermometer reads 39.2 C. Convert this temperature to degrees Fahrenheit using F = 9C/5 + 32.
- 2 A forehead thermometer reads 100.4 F. Convert this temperature to degrees Celsius using C = 5(F - 32)/9.
- 3 A patient has just run outside in cold weather and is measured with a forehead infrared thermometer. Explain why the reading might be lower than the patient's core body temperature and suggest a better measurement approach.