Also in this week's column:

• Can you become intoxicated by the power of suggestion?
• Why can't I remember my own birth?
• Why don't we suffer from e. coli all the time?

Asked by Mick Higgins of Toronto, Canada

Human body temperature is a measure of the body's ability to keep, generate, or get rid of heat as the need arises. The body is very adept at maintaining temperature within a narrow and safe range, despite occasional huge variations in the room temperature.

But some bodies are more efficient than others. Even bodies of the same height and weight may differ dramatically in the ability to maintain body temperature.

Humans also differ in their preferred room temperature. Some like it warmer, some cooler. This is called thermal comfort. Thermal comfort is not merely physical, but psychological too. In one's choice of preferred temperature, besides psychology, other personal factors come into the equation. Two of these are clothing levels (their insulation value) and activity level (their effect on body metabolism).

Stephen Turner, an engineer with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) in Atlanta, said: "Activity level is a key factor, as illustrated by the story of an adult skiing down a mountain with a child bundled in warm clothes on their back. At the bottom of the hill, the adult is sweating, but the child is bitterly cold. Difference in metabolic rate is the cause."

ASHRAE maintains and periodically revises international thermal comfort standards. But this is not the end of the story.

According to Paul Spry, a consultant engineer in Canberra, Australia, there is also evidence that a person's thermal comfort perceptions are influenced by external factors such as recent weather.

He adds: "Another consideration is the difference between sensory and psychological reactions. A particular person may say it is cold or cool, but if you accept this as the final judgment (as a desire for a higher temperature) you are at risk. Further questioning may reveal that though the person is 'cold' or 'cool' they may be optimally comfortable (desire no change for thermal comfort reasons)."

Interesting facts

• When you are hot, the blood vessels in your skin expand (dilate) to carry the excess heat to your skin's surface where it is released. You sweat and as the sweat evaporates, it cools the body.
• When you are cold, your blood vessels in your skin narrow (contract) so that blood flow to your skin is reduced to conserve body heat. You may start shivering, which is involuntary, experience rapid contraction of the muscles. This extra muscle activity helps generate more heat. Both processes help keep your body temperature with the required narrow and safe range.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

Related stories

• What is a Confessing Sam? (1 September 2006)
• What conditions disqualify you from donating blood? (25 August 2006)
• Will eating spinach make me strong? (18 August 2006)
• What are zombie behaviours? (11 August 2006)
• Was human skin really used in book binding? (4 August 2006)
• Can you die from testing a 9V battery on your tongue? (28 July 2006)