What is a normal body temperature?

There is no universally accepted normal body temperature – some medical textbooks state it as 36.8°C (98.24F), some as 37°C (98.6°F), and some just give a range such as 36.1°C to 37.2°C (96.98°F to 98.96°F). A review that analyzed 36 studies (7636 people) calculated the average body temperature to be 36.59°C (97.86°F) with a range of 36.16°C–37.02°C (97.08°F–98.64°F). Body temperature can vary depending on:

• Where the measurement is taken (for example, under the tongue, in the ear, under the armpit, in the rectum, on the forehead) – temperature readings in the armpit are lower than in the mouth; readings from the ear and rectum are higher than from the mouth)
• What type of thermometer is used (for example ones that contact the body, don’t contact the body, or just thermally scan the person)
• The time of the day the temperature is taken (our bodies tend to warm up during the day)
• How warm the environment is (body temperature tends to rise in a hotter environment and lowers in a colder environment)
• How active you are, especially immediately before your temperature is taken (your core body temperature increases the more physically active you are)
• A person’s weight (heavier people have higher body temperatures)
• A person’s age (our ability to regulate our body temperature decreases as we age so older adults tend to have a lower body temperature and younger people have higher body temperatures)
• A person’s sex (hormone levels can affect temperature)
• A person’s race.

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What is a fever?

Again, no universally accepted temperature has been accepted as one that defines a fever. In the late 1800s Carl Reinhold Wunderlich defined a slight fever as 38°C–38.4°C (100.4°F–101.1°F), a moderate fever as 38.5°C–39°C (101.3°F–102.2°F), and considerable fever as 39.5°C–40.5°C (103.1°F–104.9°F), with the lower level of the range considered as the cutoff for the morning.

Respected textbooks, such as Harrison’s Principles of Internal Medicine define fever as the following, according to the site it is measured at:

• Rectal: 37.5°C–38.3°C (99.5°F–100.9°F)
• Under the arm: >37.2°C (>99°F)
• Under the tongue (6 am/morning): >37.2°C (>99°F)
• Under the tongue (4-6 pm/late afternoon): >37.7°C (>99.9°F)

Many elderly people have a reduced ability to develop fever, and their temperature may only rise slightly even with a severe infection.

Textbooks may also define fever as a temperature higher than your normal body temperature, or specifically say fever is when your temperature is 1.1°C (2°F) above your normal temperature.

But if you don’t know your normal body temperature then generally speaking a fever is when your temperature taken under your tongue is greater than 37.8°C