This is a phenomenon known as Photic Sneeze Reflex. Another name is Autosomal dominant Compelling Helio-Ophthalmic Outburst syndrome. Yep, that spells "ACHOO", and some call it "ACHOO Syndrome".

Ever walked outside on a sunny day, only to be ambushed by a sudden, unstoppable sneeze attack? You're not alone, it's called the "photic sneeze reflex," and it's as weird as it sounds. Imagine ...

ACHOO syndrome, aka photic sneeze reflex, is relatively harmless but may affect certain careers. What usually makes you sneeze? For most, it's typically dust, pollen, or some other unwelcome invader.