Just like your weight, and many other properties of your body, your temperature often goes up and down during the day. In any one day your temperature might range from about 37.5°C during the day to about 36.4°C while you are asleep. Scientists call this natural daily change the circadian rhythm. These are the kinds of temperatures you get when a thermometer is placed under your tongue.
All skin measurements are more variable because the body uses the skin to control its temperature by radiating heat away, and by losing heat to the air by evaporating sweat. The peak daily temperature for skin measurements lags about three hours behind the core of the body. Skin temperatures are also more affected by outside things, such as clothing and air temperature
Did you know that your body can also be up to 0.5°C (0.9°F) higher or lower from one day to the next, and that your normal body temperature can be slightly different to all of those around you? Your body temperature also changes when you are hungry, sleepy, sick, or cold. Of course, after you have been exercising or playing games, your body temperature also rises. Elderly people have slightly lower body temperatures than young people. Which all goes to show that we shouldn't take too much notice of exact temperatures. When doctors measure temperatures, they look to see if your temperature is in a normal range of 36.3 and 37.3°C (97.3 and 99.1°F).
Exercise raises body temperatures, as does eating or drinking anything with calories. The more calories you eat, the more heat that is given off digesting them. This is why you feel a warm glow after eating.
Sometimes your body temperature seems to get out of control, and you get very hot and sweaty. At the same time, you feel generally unwell and tired, and often have a headache or stomach ache. This is because your body is trying to cope with an infection. It does this raising the temperature as well as creating more killer white cells in your blood.
An early morning temperature higher than 37.2°C (99.0°F) or a late afternoon temperature higher than 37.7°C (99.9°F) is something to be a little concerned over, but this is often put right by the body, and helped by a medicine such as ibuprofen.
A doctor starts to be concerned when your body temperature goes way above the normal (going below is very rare unless you are exposed to extreme cold conditions). Something over 40.0 or 41.0°C (104.0 or 105.8°F) is normally connected to some kind of fever.
Temperatures at or above about 40°C (104°F) can be life-threatening and need the advice of a medical professional.
