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Fever

General Information

In most clinical situations, fever does no major harm, and may actually benefit the human body by helping it to fight off infection. Nevertheless, fever is an abnormal finding. It can signal a serious illness, especially in adults who are old, frail, or have a weakened immune system.
Adults tend to run lower fevers than children. Fever may be further blunted or even absent in elderly patients.
Fever itself can cause muscle aches, nausea, lightheadedness, weakness and headache.

Normal Body Temperature

98.6 F (37 C) is the oral temperature that most physicians, nurses, laypersons, and medical references state is "normal."
The average temperature of healthy elderly patients is the same as younger adults. However, there is some data to suggest that the average temperature in chronically ill elderly patients is lower than that of other healthy adults. Thus, interpretation of a temperature reading in a chronically ill elderly adult must be done with caution. Because lower baseline temperatures can be expected in this group of patients, it may be easy to miss a fever if the conventional fever definition is used.

Normal Variations in Body Temperature

There is a normal daily awake-sleep cycle variation in temperature, with the low occurring at 6 AM and the high occurring at 6 pm. The low and high temperatures vary by 0.9 F (0.6 C).
In women, temperature increases about 0.9 F (0.6 C) at the time of ovulation.
Temperature can go up in response to physical activity, particularly during hot weather.