Body temperature is a measure of your body's ability to make and get rid of heat. The body is very good at keeping its temperature within a safe range, even when temperatures outside the body change a lot.
- When you are too hot, the blood vessels in your skin widen to carry the excess heat to your skin's surface. You may start to sweat. As the sweat evaporates, it helps cool your body.
- When you are too cold, your blood vessels narrow. This reduces blood flow to your skin to save body heat. You may start to shiver. When the muscles tremble this way, it helps to make more heat.
Your body temperature can be measured in many places on your body. The most common ones are the mouth, the ear, the armpit, and the rectum. Temperature can also be measured on your forehead.
Thermometers show body temperature in either degrees Fahrenheit (°F) or degrees Celsius (°C). In the United States, temperatures are often measured in degrees Fahrenheit. The standard in most other countries is degrees Celsius.
Normal body temperature
Most people think a normal body temperature is an oral temperature (by mouth) of 98.6°F (37°C). This is an average of normal body temperatures. Your normal temperature may actually be 1°F (0.6°C) or more above or below this. Also, your normal temperature changes by as much as 1°F (0.6°C) during the day, depending on how active you are and the time of day. Body temperature is very sensitive to hormone levels. So a woman's temperature may be higher or lower when she is ovulating or having her menstrual period.
A rectal or ear temperature reading will be a little higher than an oral reading. A temperature taken in the armpit will be a little lower than an oral reading. The most accurate way to measure temperature is to take a rectal reading.
In most adults, a fever is an oral temperature above 100.4°F (38°C) or a rectal or ear temperature above 101°F (38.3°C). A child has a fever when his or her rectal temperature is 100.4°F (38°C) or higher.