Police officers in the Philippines have been banned from picking their noses on duty to stop them "creating a negative impression" in public. But why, despite disgusted reactions, is this particular bad habit so enduring?

One reason humans find nose picking so rewarding is because the parts of the cortex connected to the hand and the face are so close together. Buried in the central sulcus of the brain, a groove down the side of the middle of your head, is a map-like representation of the entire surface of the body, called the homunculus.

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The body is three dimensional, but as the cortex is like a sheet of paper scrunched up to fit inside the skull, to fit it on to a 2D map requires certain cuts and juxtapositions. So, the representation of the hand ends up adjacent to the representation of the face. This nearness probably explains in part why touching the face and playing with the lips, nose and cheeks feels so satisfying.

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It is also why, sometimes, amputees who experience "phantom" itches in their non-existent limb, can relieve these by scratching their face. Doesn't make seeing other people's bogies any nicer, though.

• Dr Daniel Glaser is director of Science Gallery at King's College London