Also in this week's column:

• If whales can communicate by telepathy, why can't humans?
• You think you know about the brain?

Asked by Nikki Boyle of Newtown, NSW, Australia

Scratching an itch is a puzzling biological and behavioural response in any case. It is especially odd to scratch a healing wound since logic would indicate that scratching would hinder rather than help the healing.

One theory of why we itch suggests that scratching stimulates the release of endorphins. These are naturally occurring opiates which block pain sensation. We release a flood of endorphins to block the pain of the initial injury, while the scratching only injures our skin only a little more. The gain from the endorphins thus outweighs the loss from the slight injury.

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

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• Does urinating after sex prevent catching HIV or other infections? (27 January 2007)
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• Is it true that a woman's breasts can grow enormously overnight? (13 January 2007)
• Is there such a thing as frigidity? (23 December 2006)
• How the 'true blue' political maverick gave the senate to the donkeys (9 December 2006)
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