Is your temperature normal?

Definition of a fever is arbitrary

Doctors are often quick to dismiss the concerns of patients who feel feverish but have “normal” temperatures, saying something like, “You only have a temperature of 99 point something. That’s not a fever.”

But if you feel as if you have a fever, you probably do.

According to the Centers for Disease Control and Prevention, a fever is present when the patient “feels warm to the touch or gives a history of feeling feverish.” The CDC, however, also offers an alternate temperature-based definition of fever, with a threshold of 100.4 degrees Fahrenheit (38 degrees Celsius).

The Infectious Diseases Society of America acknowledges that “the definition of fever is arbitrary” but likewise goes on to cite various definitions, including: an oral temperature of 100 or greater; repeated oral temperatures of 99 degrees or greater; and an increase in temperature of more than 2 degrees over the patient’s baseline.

Much of what we know about fever and “normal” temperatures comes from research in the 1860s by Dr. Carl Reinhold August Wunderlich, the German physician who recorded more than 1 million temperature readings in 25,000 patients. His landmark work led to the adoption of 98.6 degrees Fahrenheit as the definition of the average normal temperature.

But pay attention to the word “average.” Normal body temperature varies from person to person, with baseline temperatures generally ranging from 1 degree above 98.6 to 1 degree below.

Furthermore, our body temperature is not a constant. It fluctuates predictably over the course of the day. Body temperature peaks in the late afternoon and hits its nadir in the early morning. This circadian rhythm can lead to variations of as much as 1 degree higher or lower.

Choice of thermometers can also add to the confusion. A rectal thermometer is the gold standard, as it comes closest to approximating the body’s core temperature. Other types, such as oral thermometers, tympanic or ear thermometers, or forehead thermometers, are more convenient but can yield lower readings.

In addition, normal temperatures tend to vary among certain groups. Women tend to have a slightly higher basal temperature than men. Older adults tend to have lower temperatures than younger people. And other people could simply be outliers.

What’s your best bet is to determine your baseline temperature? Measure your temperature when you are feeling well.

Do this using the same thermometer at the same time of day for several days, and record the results to get an average temperature. Repeating your measurements helps maximize accuracy.

When you feel feverish, remind your doctor of your baseline reading. And if your doctor says you don’t have a fever, remind him of the CDC’s definition that fever is present when the patient “feels warm to the touch or gives a history of feeling feverish.”