Why do some people sneeze when leaving a relatively darkened building and heading out into the bright sunshine?
This phenomenon, relatively unexplained by modern science, is known as the photic sneeze reflex. According to Roberta Pagon’s 2002 article in Scientific American titled, Why Does Bright Light Cause Some People to Sneeze, this kind of reflexive sneezing caused by sunlight or, occasionally, other bright lights affects roughly 18-35% of the population. This means up to a third of the population has experienced this sensation but most would be hard pressed to explain why it happens to them.
Genetic Component
The photic sneeze reflex is known to be genetically linked. If you experience these events, you inherited the trait from either your mother or your father. Beyond this information, little has been determined about the cause and evolutionary drive behind “sunshine sneezes.”
Historical Scientific Theories
The phenomenon has been discussed by thinkers as far back as Aristotle, who felt that perhaps the heat of the sun on the nose elicited the response. However, closing or shading the eyes seems to prevent the reflex, indicating that Aristotle was not quite on track scientifically with this theory. If the heat is still there but the sneeze can be prevented that must not be the cause.
Others have argued that bright light causes the eyes to water and the moisture irritates the nasal passages. Francis Bacon was an early author of this theory. But modern science now shows that the sneeze effect takes place too quickly to be the result of a chain of physiological events.
Modern Scientific Theories
Recent theories indicate that perhaps the wiring in the brain is responsible. According to a 2008 Scientific American article by Karen Shrock, Looking at the Sun Can Trigger a Sneeze, “a sneeze is usually triggered by an irritation in the nose, which is sensed by the trigeminal nerve, a cranial nerve responsible for facial sensation and motor control. This nerve is in close proximity to the optic nerve, which senses, for example, a sudden flood of light entering the retina. 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. Hence, a sneeze.”
The condition has been considered relatively harmless and, therefore, has not been the subject of many rigorous scientific studies. However, noting the relation between light triggers and more serious conditions, since as epilepsy and migraine headaches, some scientists are beginning to become interested in the occurrence of this condition. Since it is known that flashing lights can trigger epileptic seizures, and migraines are frequently accompanied by visual anomalies, researchers believe that understanding the mechanisms behind the photic reflex sneeze may lead to better understanding of the neural pathways related to these disorders.
If walking into the bright sunshine causes you to sneeze, don’t be alarmed. You share this experience with a large portion of the population and it is not directly linked to more serious medical concerns but is merely an inherited trait. Just enjoy the sunshine.
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