Photic sneeze reflex
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Photic sneeze reflex (also referred to as sun sneezing, photogenic sneezing, or whimsically called ACHOO syndrome, a backronym for Autosomal dominant Compelling Helio-Ophthalmic Outburst syndrome) is a medical condition by which people exposed to bright light sneeze. The photic sneeze reflex can also cause one to sneeze many times consecutively. The condition occurs in 17% to 25% of humans, with more common occurrence in Caucasians than others. The condition is passed along genetically as an autosomal dominant trait.
The first mention of the phenomenon is probably in the later work attributed to Aristotle (Problems, book XXXIII).
The probable cause is a congenital malfunction in nerve signals in the trigeminal nerve nucleus. The fifth cranial nerve, called the trigeminal nerve, is apparently responsible for sneezes. Research suggests that some people have an association between this nerve and the nerve that transmits visual impulses to the brain. Overstimulation of the optic nerve triggers the trigeminal nerve, and this causes the photic sneeze reflex. Another theory suggests that tears leaking into the nose through the nasolacrimal duct are a cause of the photic sneeze reflex. The speed of the reflex seems to favour the first theory, as it happens much too quickly for tears to be generated and drain into the nose. In addition this sneeze reflex can be brought on by a sudden inhaling of cold air or a strong flavor such as a strong mint gum. This implies an overstimulation of any nerve close to the trigeminal nerve can cause the sneeze reflex.
[edit] References
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