A thermometer measures body temperature. The common sites for measuring body temperature are the oral cavity, axillary region, temporal artery, and skin surface, such as the forehead, abdomen, and axilla. True core body temperature is assessed in the rectum, tympanic membrane, pulmonary artery, esophagus, and urinary bladder.

Oral: When assessing oral temperature, the thermometer tip should be placed under the tongue in the posterior sublingual pocket. It offers accurate readings and can be used on intubated patients. Limitations for this measurement include readings affected by recent hot or cold food consumption, use on certain patients such as oral surgical patients, and risk of cross-infection with oral thermometer use.

Tympanic Membrane: The temperature of the tympanic membrane is considered the core body temperature. It is measured using a thermometer with infrared sensors that detect heat emitted by the tympanic membrane. This method offers advantages such as easy accessibility, high accuracy in critically ill patients, quick measurement, and minimal repositioning. However, there are limitations, including measurement variations, the need to remove hearing aids, and the potential for distorted readings due to factors like ear infections or surgery. Additionally, it is unsuitable for continuous measurement and can be affected by environmental temperature devices. Care should be taken when using it in infants and young children due to the anatomy of the ear canal. Correct positioning is crucial to ensure accurate results.

Rectal: Rectal temperature is considered one of the most accurate core temperature measurements. It is a reliable alternative when oral temperature measurement is difficult. However, some disadvantages include potential discomfort, bodily fluid exposure risk, and specific individual limitations.

Skin: Temperature can be measured at various skin areas, including the forehead, abdomen, and underarms. Advantages of this method include its affordability, continuous reading capability, non-hazardous nature, and suitability for newborns. However, there are some disadvantages to consider. Such limitations include measurement lags, which can occur during temperature fluctuations; adhesion, which may be hindered by sweating; reading accuracy, which can be affected by the environmental temperature; and unsuitable for individuals with adhesive allergies.

Temporal Artery: Measuring temperature via the temporal artery lends to several advantages. It is a quick, efficient, and easy method to perform and does not require any major patient position change, clothing, or swaddle removal to access the measurement site. The risk of harm or injury to the healthcare professional or patient is minimal with this method. Measuring the temporal artery does not require using sensor covers, simplifying the measurement process.

Axillary: The axillary site is an alternative for temperature measurement when oral and rectal sites cannot be used. It is safe, low-cost, and reliable for stable-term and preterm newborns. However, it has disadvantages, including prolonged measurement periods, continuous positioning, lagging behind core temperature during fast fluctuations, and underestimation of core temperature. It is not recommended for detecting fever and may result in temperature loss in neonates due to exposure to the thorax. Additionally, environmental exposure and time to correctly place the thermometer probe can affect accuracy.