Oral temperature measurement is a common, straightforward method to screen for fever, providing an estimate of the body’s internal core temperature. This involves placing a thermometer under the tongue, a location that reflects systemic temperature changes. Achieving an accurate reading depends entirely on following the proper technique, especially the duration the thermometer remains in place, which is determined by the device’s technology.
Required Time for Accurate Oral Readings
The time a thermometer must be held in the mouth varies significantly between modern digital models and older glass devices. Digital thermometers use fast-acting heat sensors that rapidly detect temperature changes. These devices typically require 30 seconds to one minute before emitting a signal that indicates the peak temperature has been registered. Removing the digital thermometer before this audible signal will likely yield an inaccurately low reading because the sensor has not yet stabilized.
Older glass thermometers, which may contain alcohol or mercury, rely on the physical expansion of liquid, a process that takes much longer. For these devices, a waiting period of approximately three minutes is required for an accurate reading. Some recommendations suggest holding the glass thermometer in place for up to five minutes to ensure the reading is stable. Glass mercury thermometers are no longer recommended due to safety concerns, making digital models the preferred choice for at-home use.
Factors That Skew Oral Temperature Results
The temperature of the oral cavity can be temporarily altered by external factors, making preparation a crucial step before taking a reading. Consuming hot or cold food and beverages directly influences the mouth lining temperature, causing a falsely high or low reading. Smoking also produces a temporary change in oral temperature that affects the measurement.
To ensure the reading reflects the body’s core temperature and not the mouth’s surface temperature, a specific waiting period is necessary before inserting the device. Experts advise waiting at least 15 minutes after eating, drinking, or smoking. Waiting 30 minutes is a more conservative approach, allowing the mouth temperature to fully normalize. Neglecting this preparatory waiting time frequently causes inaccurate temperature measurements.
Understanding Your Temperature Reading
Once the thermometer signals completion, understanding what constitutes a normal temperature is the next step. While the historical average is often cited as 98.6°F (37°C), the normal oral temperature range for a healthy adult is broad, typically falling between 97.6°F and 99.6°F (36.4°C and 37.5°C). An individual’s temperature can fluctuate slightly throughout the day due to factors like activity level, time of day, and hormonal changes.
For most adults, a fever is defined as an oral temperature of 100.4°F (38°C) or higher. A reading between 99.5°F and 100.3°F may be considered a low-grade fever, though this range is not universally standardized. If a fever is over 103°F (39.4°C), or if a moderate fever persists for more than five days, contact a healthcare professional for guidance.