In a human, the core body temperature is regulated by a part of the brain called the hypothalamus located at the base of the brain. Body temperature is a good indicator of one's health, and is usually part of any hospital or doctor visit as well as a tool for self evaluation at home.
In 1868, German doctor, Carl Wunderlich, published a paper that identified the average body temperature as being 98.6 degrees. He obtained data from 25,000 adults by taking more than 1 million measurements of temperature. He found that, while temperatures of healthy individuals varied, they averaged 98.6 degrees. His data is awesome, since the thermometers took 15 or 20 minutes to obtain a reliable temperature and had to be read while they were still in place in the armpit. Physicians today do not normally use such underarm readings because of their unreliability.
The number from this study still stands in textbooks, although the results from a large study in 1992 suggests that a value of 98.2 might be more accurate. It seems that one's baseline temperature can vary slightly and may consistently be a little higher or lower than any one standard value that has been proposed.
A person's body temperature will vary depending on several factors such as: a person's age, sex, and degree of activity level; the time of day, typically being lowest in the early morning and highest in the late afternoon; food and fluid intake; for women, the stage in their monthly menstrual cycle; and the method of measurement, such as mouth, rectal, armpit, ear or an infrared thermometer passed across the forehead. Each method may give a slightly higher or lower value than the actual core body temperature.
In addition, one's temperature can vary by as much as 2 degrees either side of the accepted standard for an individual. In an adult, a temperature more than 100.4 degrees is usually an indication that one has a fever caused by an infection or illness.
It has been reported that certain medical conditions can affect a person's core body temperature. For example, people with an underactive thyroid gland tend to have lower temperature readings, while people with certain cancers can have higher readings. Babies and small children have temperature values and issues that are not the same as those of older children and adults and need to be treated keeping those differences in mind.
Larry Stone is a retired Dana College science professor.