Sarah McDonald, of Cromwell School, asks :-

Why do our teeth chatter when we are cold?

Chris Bolter, a physiologist at Otago University's School of Medical Science, responded.

If you feel cold and your teeth are chattering, it means that you're shivering. Teeth chatter when our jaw muscles contract rapidly and involuntarily. When muscles contract like this they produce a lot of heat that helps to warm the body.

Normally, our body temperature is maintained close to 37°C. If the brain detects that body temperature is falling below normal, it sets up a number of responses. An immediate and effective response to a small drop in body temperature (as little as about 0.1°C) is that we feel cold and we modify our immediate environment. We might put on more clothes, go indoors, or light a fire i.e. we do something that will immediately reduce the amount of heat we lose, or create a source of heat.

The brain also starts up a number of unconscious involuntary responses. With a small drop in body temperature blood flow to skin decreases, and this reduces the amount of heat that leaves the body (your skin might appear paler). With a slightly larger drop in body temperature, about 0.5°C, the limbs start to shiver. Whole body shivering that involves muscles of the trunk and face will occur when body temperature drops a little more. At this stage your teeth may chatter.

When shivering starts, the body temperature is usually well above the value considered to represent the potentially dangerous state of hypothermia this occurs below 35°C. However, shivering is a sign that the body ought to be rewarmed, and practical efforts should be made to rewarm the body and to prevent the body temperature from falling further.