Bright light makes you sneeze. It seems like one of those fake news that you often come across on the web, but it isn't. In fact, it seems that many people in the presence of bright light cannot help but sneeze. This is a reflection that affects 15-30% of the population and that "affects" especially those with green eyes.

Sneezing usually serves to rid the nose of germs and impurities, yet there are cases in which some people exposed to sudden sunlight, photographers' flashes or other light sources respond with a sneeze.

The British call it ACHOO syndrome (Autosomal dominant Compelling Helio-Ophtalmic Outburst) and it is no coincidence that the reference to onomatopoeia, for us it is the photic reflex sneezing or (photoptarmosis).

Although it is a rather widespread syndrome, it should be noted that it is not a serious medical condition.

But where does the photic reflex sneeze come from?
There is still no univocal explanation, but there are several theories that would explain its origin. Let's find out together:

- INTERFERENCE BETWEEN OPTICAL NERVE AND TRIGEMINUS
The intense activation of the optic nerve that responds to light could stimulate the nearby trigeminal nerve, which is responsible for some facial movements. The brain could then mistake the light stimulus as a nose irritant, and respond accordingly.

- EVOLUTIONARY RESIDUE
For some reason that is not clear to us, at some point in our evolutionary history, sneezing in the presence of sudden light had to be "beneficial" and this reaction has somehow made it to this day, manifesting itself in 15-30% of the population.

- REACTION DEEP ROOTED IN THE BRAIN
According to a Swiss study from a few years ago, the visual cortex of those who sneeze to light is more easily excitable and therefore more sensitive than that of individuals who do not have this reaction. The photic reflex sneeze would therefore be an even deeper response than the reflex that prompts us, for example, to remove our hand from the still hot gas plate.

- ACTIVATION OF THE PARASYMPATHIC NERVOUS SYSTEM
Exposure to light would activate the parasympathetic nervous system, responsible for involuntary actions. In front of a luminous flash we dilate the pupils, frown, actions that could spontaneously provoke another reflection, that of the sneeze. However, it would not explain why then only some people sneeze in the light: a reaction that some studies hypothesize is genetic.