What it is
You walk out of a dim room into sunshine. A moment later you sneeze, sometimes two or three times. It isn't an allergy to the sun and it isn't hay fever. The trigger is the sudden change from dark to bright.[7]
In 1978 four doctors gave it a name that spells out a sneeze:[1]
- A
- Autosomal dominant
- C
- Compelling
- H
- Helio-
- O
- Ophthalmic
- O
- Outburst
Roughly: an inherited, hard-to-stop burst of sneezing set off by sunlight hitting the eyes. It can run in families. If one parent has it, each child has a one in two chance of inheriting it.[6]
More on the name, the theories and the genetics
Common, and easy to miss
In a British sample, about one in four people sneezed in response to bright light.[2] A study of 3,417 people in China put it at 25.6 percent.[3] Other surveys have found far fewer or far more, depending on who was asked and how, so treat any single number with care.[12, 11]
A sneeze closes your eyes
Mostly it's a passing nuisance. It matters when you're driving out of a tunnel into daylight, because you can be dazzled and shut your eyes mid-sneeze at the same moment.[7] Aviation doctors have flagged the same risk for pilots.[5]
Know the name
If this is you, you're not making it up, and you're far from alone. Use the name. Tell the person in the passenger seat, your driving instructor, or the eye doctor about to shine a bright light in your face.
achoosyndrome.org