Why Some People Start To Sneeze When They See The Bright Sunlight?
Why some people start sneezing or scratching their noses when they are suddenly exposed to bright light, especially sunlight?
This interesting physical reaction is called photic sneeze reflex (also called photoptarmosis or ACHOO - Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome) and had been the subject of research since the times of Greek philosopher Aristotle (350 BCE). Aristotle thought it had something to do with heating the moisture inside of the nose, but later, in 17th century, Francis Bacon refuted this hypothesis by realizing that the reflex did not occur when the eyes were closed. He concluded that the eyes must be the culprit, so he hypothesized that the sunlight causes the eyes to emit tears, which then flow down to the nasal cavities prompting the irritation.
The possible cause of this syndrome was more deeply researched in 1964 when physician Henry Everett proposed in his study that photic sneeze reflex has to be linked to our nervous system and how it processes the impulses from the eyes and the nose. How this reflex really works is still not yet fully understood but the scientists has suggested that it may be because our eyes, nose and face are all possibly connected to the trigeminal nerve. So when our eyes are suddenly stricken by bright sunlight, the brain may confuse the visual stimulus with the nasal one. Another hypothesis is that it is due to the effect called "parasympathetic generalization" - neurons in the brain responsible for processing the information from the eyes may automatically activate neighboring neurons responsible for the sneezing.
The photic sneeze reflex seems to be hereditary and affects between 18-35% of people depending on geographical location.
It has also been proven to be quite dangerous. For example, it can affect the automobile drivers when they suddenly leave the dark tunnel driving right into very bright sunlight. Similarly the airplane pilots are at risk due to sudden loss of concentration and precise control of the plane caused by uncontrolled outbursts of sneezing. The military study in 1993 on combat pilots discovered that using sunglasses can prevent this reflex from occurring.
"Photic sneeze reflex", Wikipedia article.
"Looking at the Sun Can Trigger a Sneeze", Scientific American, 2008.
"Why does bright light cause some people to sneeze?", Scientific American, 2009.
"When the Sun Prickles Your Nose: An EEG Study Identifying Neural Bases of Photic Sneezing", Public Library of Science, 2010.
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