Normal oral body temperature in adults is approximately 37°C (98.6°F), though healthy temperatures typically range from 36.1°C to 37.2°C (97°F to 99°F). Individual variation is natural and depends on factors like time of day, age, activity level, and measurement technique.
Oral temperature is one of the most common ways to measure body heat because the mouth provides a relatively stable environment for an accurate reading. Temperature naturally fluctuates throughout the day, generally being lowest in early morning and highest in late afternoon or evening. Physical activity, stress, and certain foods can temporarily raise oral temperature.
For accurate oral measurement, a thermometer should be placed under the tongue with the mouth closed for the time specified by the device—typically 30 seconds for digital thermometers or longer for older mercury versions. Eating, drinking, or smoking shortly before measurement can affect accuracy, so waiting 15-20 minutes after these activities is recommended.
It's worth noting that oral temperature readings are lower than rectal measurements (the most accurate method, typically about 0.5°C higher) and higher than axillary (armpit) readings. Different populations have slightly different normal ranges—fever thresholds for infants and children may be interpreted differently than for adults. When concerned about health, comparing temperature readings taken under consistent conditions over time is more useful than relying on a single absolute number.