It’s not an allergy…
If you sneeze when suddenly exposed to sunlight or other bright lights, you’re not alone: research estimates that up to 30% of all humans share this peculiar trait, known as the “photic sneeze reflex.” Even Aristotle documented his confusion on the matter, writing in his Book of Problems: “Why does the heat of the sun provoke sneezing, and not the heat of fire?” While it’s actually light, not heat, which triggers the sneezing, Aristotle proves that photic sneezing has a rich history of puzzling humankind. Centuries later, the answer still manages to elude us.
While bothersome, photic sneezing does not pose any real medical danger, and thus not much funding has been devoted to its scientific investigation. However, scientists do have a few prevailing theories as to why this curious phenomenon exists.
Photic Sneeze Theories
Sneezing is a biological reflex signaled by the brain to clear the mucus lining of foreign contaminants, in order to effectively reset the nasal environment. Scientists have fondly referred to it as a sort of CTRL + ALT + DELETE for your nose. Usually, this reflex is triggered when nerves detect an irritant in the mucus lining, notifying the brain to activate a sneeze in order to expel the intruders. Recent research suggests that sneezing serves the additional purpose of kickstarting the cells’ cilia into high gear for the next several minutes, to aid in evacuating contaminated mucus from your nasal passages.
Why, then, does bright light trigger sneezing in so many people? Scientists have still yet to understand it, but they have coined an endearing, formalized term for the condition: ACHOO, for “autosomal dominant compelling helio-ophthalmic outburst” syndrome. While the mechanism is not yet entirely clear, researchers have proposed two prevailing theories to explain this puzzling phenomenon:
- A miswiring between the optic and trigeminal nerves: Some scientists speculate that photic sneezing may be caused when the optic nerve gets crossed with the trigeminal (fifth cranial) nerve, resulting in a sneeze in response to light stimulation. Karen Shrock of the Scientific American explains, “As the optic nerve fires to signal the brain to constrict the pupils, the theory goes, some of the electrical signal is sensed by the trigeminal nerve and mistaken by the brain as an irritant in the nose.” Other scientists suggest that some individuals may possess a genetic variation which positions the optic and trigeminal nerves in closer contact, although the exact neurological pathway responsible remains unknown.
- Parasympathetic generalization: Another theory suggests that with “parasympathetic generalization,” activation of one part of the parasympathetic nervous system excites other parts as well. Following these lines, the constriction of the pupils in response to light may indirectly trigger congestion in the mucus membranes, resulting in a sneeze. If correct, this theory may also explain why some people sneeze in response to feeling full, or even when aroused.
In 2010, researchers from the genetic testing company 23andMe identified two distinct nucleotide polymorphisms (SNPs) linked to the photic sneeze reflex, one of which is located close to the gene associated with light-induced epileptic seizures. Doctors are hoping that as more knowledge on the photic sneeze reflex is discovered, it can also be applied to the study and treatment of epileptic seizures.
Is Sun Sneezing Dangerous?
Photic sneezing in and of itself does not pose any medical danger, nor is it a symptom of an underlying medical condition. However, when triggered inconveniently, it can have dire consequences.
Drivers with the photic sneeze reflex have reported concern when driving through tunnels, as the sudden exposure to sunlight upon leaving activates a set of 2-3 consecutive sneezes, temporarily impairing their ability to drive. Of greater concern is the fact that this sneezing fit also results in momentary blindness in most drivers. Studies have outlined the same danger posed to combat pilots, as well as their commercial counterparts.
Fortunately, there is a simple solution that tends to work for many sufferers: sunglasses.
Schedule a Consultation With Dr. Shukla
If respiratory symptoms are impacting your daily life, schedule a consultation with respected pulmonologist Dr. Mayank Shukla at the Asthma Allergy Sleep Center of New York for better breathing today.