Also in this week's column:

• Why are people so often in denial?
• Can flossing your teeth prevent a heart attack?
• What is the difference between a virus and a bacterium?

Asked by Ingrid Smith of Chatswood, NSW, Australia

Theoretically, any sudden severe shock, accident, illness or change in metabolism could make hair change colour, but it won't be visible right away.

According to Dr John O'Connor, head of the School of Physical Science and Mathematics at the University of Newcastle in Australia, "once your hair has grown out of its follicle, any emotional or physical trauma will not affect it. This hair is basically dead, like your nails. Yet severe adverse events could cause new hair that grows out a few weeks later to be white."

What about turing white overnight?

Let's concentrate on "overnight". Just like in the cartoons? There is no scientific evidence that hair can turn white overnight due to some traumatic experience. However, legend has it that both Thomas More and Marie Antoinette suffered a hair colour change to white the night before their executions.

Some maintain even today that a condition called alopecia areata can turn hair white overnight. But this condition refers to hair loss, not hair colour change. Dr Douglas Nelson of Averon-Bergelle, France, described the case of a 45-year-old French farmer whose hair reportedly went from black to white in 14 days. It stayed that way for about six months. Then, over a period of four months, it grew back to full black as before. He was in perfect health. There was no illness. There was no shock. There is no explanation.

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

• Could you be addicted to the internet? (22 September 2006)
• Are there people with no sense of smell? (15 September 2006)
• Can you become intoxicated by the power of suggestion? (8 September 2006)
• 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)