An Intro to Photic Sneeze Reflex

6. How Photic Sneeze Reflex Works

Photic sneeze reflex makes little sense to most people: after all, the sun is not an allergen. The entire purpose of sneezing is to flush out irritants from the nose. Light is not an irritant in this sense. PSR has not been researched in any detail as it does not directly cause harm. Only a few dozen case studies and medical journals delve into the issue. One theory places responsibility with the parasympathetic nervous system. As mentioned previously, another theory proposes that the optic nerve is to blame: when sending signals to the brain to constrict one's pupils, the trigeminal nerve mistakenly takes this as a signal that the nose needs to expel an irritant. Yet another theory is that the optic and cranial nerves cross, resulting in the violent sneezing fits.