A normal body temperature when measured orally is around 98.6 degrees Fahrenheit or 37 degrees Celsius, according to WebMD. It is normal for body temperature to fluctuate as much as one degree above or below 98.6 degrees throughout the day.
WebMD further explains that normal body temperature fluctuates in response to the time of day, the activity level of the person and other factors, such as hormone levels. The most accurate way to measure body temperature is rectally. Rectal temperatures are normally slightly higher than oral temperatures. An oral temperature above 100.4 degrees or a rectal temperature above 101.4 degrees is classified as a fever.
Despite the constantly changing temperatures of human's surroundings, the body maintains a very specific temperature, explains WebMD. When the body is too hot, it begins to sweat. As the sweat evaporates, the body cools. When the body is too cold, the muscles start firing off frantically to induce shivering and force the body to make more heat.