December 01, 2018

Why does my granddaughter sneeze when she steps into the sun?

Q: My granddaughter often seems to sneeze when she steps into the sun. Is this from an allergy?

A: This phenomenon, commonly called a sun sneeze, is technically known as either photic sneeze reflex or an autosomal dominant compelling helio-ophthalmic outburst (ACHOO) syndrome. It's not linked to allergies, although there is some common ground in how the sneezes may occur.

Typically, a sneeze occurs because of irritation in the nose, such as from dust or pollen. The irritation fires the trigeminal nerve — the main cranial nerve that carries sensation from your face to your brain — to trigger the sneeze. Although the cause of sun sneezing isn't fully understood, the theory is it involves the optic nerve, which senses changes in light. When you step out of a dark room into the light, your pupils constrict. This reflex is triggered by the optic nerve. It's thought that rapid triggering may give the same sensation as an irritation in the nose, causing the same effect on the trigeminal nerve.

Sun sneezing is common, affecting 11 to 35 percent of people. While harmless on its own, sun sneezing could potentially cause issues with driving, such as with emerging from a road tunnel on a bright day. Shielding your eyes with sunglasses or your car's visor may help.