Body temperature is a foundational measurement of health. Because temperature can be taken at different external sites, such as the mouth, armpit, or rectum, questions often arise about whether the raw number needs adjustment. Understanding the correct method for reading a thermometer is important for accurately determining if a fever is present.
The Direct Answer: Oral Temperature Adjustments
With modern digital and electronic thermometers, you do not need to add or subtract any degrees from the temperature displayed for an oral reading. The number that appears on the screen is the number you should accept as the oral temperature.
The confusion about adding a degree stems from historical practice involving older glass thermometers. Years ago, the standard reference temperature was almost always taken rectally, which provides a higher reading than an oral measurement. When comparing a lower oral temperature to that higher rectal standard, a correction factor was sometimes mentally applied. Modern digital thermometers are calibrated to provide a direct, reliable reading for the specific site, eliminating the need for manual adjustment.
Understanding Core Temperature and Site Comparisons
Core temperature represents the internal temperature of the body’s organs, which is the most accurate indicator of a true fever. The rectal measurement is the closest and most consistently accurate way to estimate this core temperature. Other measurement sites, including the mouth, are considered peripheral and are influenced by the surrounding environment, leading to variations in the reading.
An oral temperature is typically lower than a rectal temperature by approximately 0.5°F to 1.0°F (0.3°C to 0.6°C). In contrast, an axillary, or armpit, temperature is often 0.5°F to 1.0°F lower than the oral temperature. When reporting a temperature to a healthcare provider, it is important to state the exact number and the location where the measurement was taken.
How to Measure and Interpret Oral Temperature
To ensure an accurate reading, proper technique is essential when taking an oral temperature with a digital thermometer. Wait at least 20 to 30 minutes after eating, drinking hot or cold beverages, or smoking, as these activities can temporarily alter the temperature of the mouth.
Place the tip of the thermometer deep under the tongue, slightly off-center, in the heat pocket near the sublingual artery. The mouth should remain closed around the thermometer until the device signals that the reading is complete, typically with a beep.
The generally accepted range for a normal oral temperature is 96.4°F to 99.1°F (35.8°C to 37.3°C), with an average often cited as 98.6°F (37°C). An oral temperature reading of 100.4°F (38°C) or higher is considered the threshold for a fever.