Why does bright light make me sneeze?

Question from Jacob Wall

This is known as the photic sneeze reflex, or ACHOO (autosomal dominant compulsive helio-ophthalmic outbursts of sneezing) syndrome. ‘Autosomal dominant’ means you only need to inherit the gene from one of your parents to have the trait. However, we still don’t know exactly how light entering the eyes can lead to a sneeze.

Answered by Jodie Tyley for Brain Dump in How It Works issue 125.

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