Most people believe that the normal oral body temperature is 98.6 degrees Fahrenheit. However, this is actually a myth that goes back over 150 years to the work of Dr. Carl Wunderlich, a German physician who researched the body temperature of thousands of patients and published his findings. However, his only finding that made it into literature was that mean body temperature is 98.6.
Wunderlich never suggested that there was one normal body temperature.
Dr. Philip Mackowiak, the director of medical care in the Veterans Administration Maryland Health Care System (and an infectious disease expert and an amateur medical historian) collected 700 temperatures from 148 healthy adults and found that their readings ranged from 96 to 100.8. This calculates to an average of 98.2 degrees (and only 8 percent of their 700 temperatures were 98.6). Mackowiak, in a 1992 article in the Journal of the American Medical Association, concluded that 98.6 should be abandoned.
Mackowiak was also able to find one of Wunderlich's termometers in a Philadelphia museum. Testing showed that termometer was calibrated a degree-and-a-half centigrade higher that the ones used today. Wunderlich also measured temperatures by taking them in the armpit, which should have made them lower than oral temperatures.
Mackowiak has said that while 98.6 isn't necessarily wrong, normal body temperature really depends on the person and can be influenced by age, gender, race, and time of day. Mackowiak suggests that an oral temperature higher than 99 in the early morning and 100 in the early afternoon can be called a fever.