Photic sneeze reflex
| Photic sneeze reflex | |
|---|---|
| Classification and external resources | |
| OMIM | 100820 |
| DiseasesDB | 30910 |
The photic sneeze reflex (also known as photoptarmosis, Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome (ACHOO) and colloquially sun sneezing) is a condition that causes variable difficulty to control sneezing in response to numerous stimuli, such as looking at bright lights or periocular (surrounding the eyeball) injection. The condition affects 18–35% of the population in the United States, but its exact mechanism of action is not well understood.
The photic sneeze effect is a genetic tendency to begin sneezing, sometimes many times consecutively (due to naso-ocular reflex), when suddenly exposed to bright light. This condition tends to occur more severely after one has emerged into the light after spending time in a dark environment. Although the syndrome is thought to affect about 18% to 35% of the human population, it is relatively harmless and not widely studied.
The photic sneeze effect has been documented for many centuries. The Greek philosopher Aristotle was one of the first to contemplate this strange phenomenon in 350 BCE, exploring why looking at the sun causes a person to sneeze in The Book of Problems: "Why does the heat of the sun provoke sneezing?" He hypothesized that the sun’s heat caused sweating inside the nose, which triggered a sneeze in order to remove the moisture. In the 17th century, English philosopher Francis Bacon disproved Aristotle’s theory by facing the sun with his eyes closed, which did not elicit the ordinary sneeze response. Bacon therefore guessed that the eyes played a vital part in triggering photic sneezing. He assumed that looking at the sun's light made the eyes water, and then that moisture proceeded to seep into the nose and irritate it, causing a sneeze. Although plausible, scientists later determined this theory to also be incorrect because sun-induced sneezing occurs too quickly after sunlight exposure; watering of the eyes is a slower process, so it could not play a vital part in triggering the reflex.
Today, scientific attention has mainly focused on a hypothesis proposed in 1964 by Henry Everett, who was the first to call light-induced sneezing “The Photic Sneeze Effect.” Since the nervous system transmits signals at an extremely fast pace, Dr. Everett hypothesized that the syndrome was linked to the human nervous system, and was perhaps caused by the confusion of nerve signals. The genetic basis of photic sneezing still remains unclear, and single genes for this condition have not been found and studied. However, the condition often occurs within families, and it has been suggested that light-induced sneezing is a heritable, autosomal-dominant trait. A 2010 study demonstrated a correlation between photic sneezing and a single-nucleotide polymorphism on chromosome 2. Further data from the genealogical site 23andMe using the genome-wide association study protocol has highlighted the role of multi-tasking genes.,
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