There’s no such thing as a normal temperature. Body temperature varies among people and tends to be lower in the morning and higher in the late afternoon. Women tend to run slightly higher than men. The 98.6°F/ 37°C norm was established by Carl Wunderlich, a 19th-century German doctor who measured body temperature in thousands of people. Newer research suggests that 98.2°F (36.8°C) is a more accurate average, at least for people 40 or younger, with an upper limit for “normal” of 99.9°F (37.7°C). One study noted that nearly all people over 65 have an oral temperature below 98.6°F (37°C).
Oral temperatures are about 1°F lower than rectal—which is probably closest to true core body temperature—and will be affected if you’ve had something hot or cold to drink within 20 minutes. Armpit (axillary) temperature is about 1°F lower than oral and may be further affected by room temperature. Body temperature may be higher if you’ve exercised or taken a hot bath within the past hour.
Most thermometers are fairly accurate. Mercury-free oral thermometers have largely replaced mercury thermometers. Hold it far back under the tongue for three minutes. Digital electronic thermometers are quick, safe, easy to read and inexpensive. Infrared ear thermometers take two seconds, are easy to read and are less likely to become contaminated. Place it precisely in the ear, aimed at the eardrum, or you may get a low reading (kids should avoid squirming). For babies, electronic “pacifier” thermometers are less reliable than a rectal thermometer. Avoid disposable forehead temperature strips.
Fever is a rise in body temperature, most commonly in response to infection, and a sign that the body’s natural defenses are working. It should be evaluated with other symptoms, such as headache, fatigue and chills. Though definitions vary, an oral temperature above 100°F (37.8°C) is generally considered a fever. Infants with a rectal temperature of 100.4°F (38°C) and higher need medical care. Anybody with a temperature above 104°F (40°C) should consult a doctor. Fevers above 106°F (41.1°C) are life-threatening and need immediate treatment. For milder fevers, whether to call a doctor depends on symptoms and how long the fever has persisted.