Why does bright light cause people to sneeze?

THAT'S THE WHY:WHEN SOMEONE suggested I write an entry for this column on why people sneeze when they suddenly see a bright light, my first reaction was: "Do they?"

Because that doesn’t happen to me. And it turns out I’m in the majority – only 25-35 per cent of the population experiences a photic sneeze reflex, where a sudden exposure to bright light can set them off.

The question of how his happens has puzzled scientists as far back as ancient Greece, but current thinking suggests it may be down to crossed wires in the brain.

You normally sneeze when an irritation in your nose is picked up by the trigeminal nerve, which kicks off a sneeze reflex to expel the irritant.

But the trigeminal nerve is close to the optic nerve, which swings into action when the eye is exposed to bright light.

So it has been suggested that in photic sneezing the trigeminal nerve senses the light-induced burst of activity in the optic nerve and that prompts the sneeze reflex.

It is considered to be hereditary, so if one parent sneezes in response to light, each of the kids has a 50:50 chance of inheriting the tendency.

And in one of the more masterful examples of medical naming, such light-triggered sneezing has been called the autosomal-dominant compelling heliopthalmic outburst syndrome . . . or the “Achoo syndrome” for short. Gesundheit!

– CLAIRE O’CONNELL