question: Why does the sun cause us to sneeze?
comment: The Sun causes some people to sneeze because random mutations have caused them to have genes that cause them to sneeze when exposed to bright light. Sneezing when exposed to bright light does not make you significantly less likely to have children than someone who doesn't sneeze when exposed to bright light, so the genes have been passed down to a significant portion of humanity. *Not* sneezing when exposed to bright light also does *not* make you less likely to have children, which is why the photonic sneeze reflex isn't present in all of humanity. This would indicate that it doesn't really do anything overly important.
passages: While this phenomenon is poorly understood, recent research has shown that antihistamines being used to treat rhinitis due to seasonal allergies may also reduce the occurrence of photic sneezes in people affected by both conditions.
  
  Those affected by photic sneezing may find relief by shielding their eyes and/or faces with hats, scarves, and sunglasses.
  
  Section::::History.
   Photic sneeze reflex
  
  The photic sneeze reflex (also backronymed as Autosomal Compelling Helio-Ophthalmic Outburst (ACHOO) syndrome and colloquially sun sneezing) is a reflex condition that causes 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 world's population, but its exact mechanism of action is not well understood.
  
  Section::::Symptoms.
   Section::::Pathophysiology.:Optic-trigeminal summation.
  
  Stimulation of the ophthalmic branch of the trigeminal nerve may enhance the irritability of the maxillary branch, resulting in an increased probability of sneezing. This is similar to the mechanism by which photophobia develops by persistent light exposure relaying signals through the optic nerve and trigeminal nerve to produce increased sensitivity in the ophthalmic branch. If this increased sensitivity occurred in the maxillary branch instead of the ophthalmic branch, a sneeze could result instead of photophobia.
  
  Section::::Pathophysiology.:Parasympathetic generalization.
   Perhaps the most universal risk of sneezing is the spread of disease. Bacterial infections can spread to susceptible uninfected people via the spread of microscopic organisms suspended in the droplets expelled by a sneeze. Bacteria which commonly spread by sneezing include bacterial meningitis, strep throat, and tuberculosis. Viral infections can also be spread by sneezing. When a virus is expelled by a sneeze, its mucous membrane evaporates, and the virus becomes a droplet nucleus which can be inhaled by another person, thus spreading the virulent infection. Examples of virulent infections that spread by sneezing include measles, mumps, rubella, and influenza.
   A study conducted by the School of Optometry at the University of Alabama at Birmingham found that females represent 67% of photic sneezers, and Caucasians represent 94%. The study also found statistically significant correlations between photic sneezing and the presence of a deviated nasal septum. The study also showed that photic sneezing is more likely to be acquired than inherited.
  
  Section::::Symptoms.:Response to periocular injection.
   When the trigeminal nerve is directly stimulated, there is the possibility that increased light sensitivity in the ocular nerve could result. An example of directly stimulating would be plucking an eyebrow or pulling hair. In many people who show the photic sneeze reflex, even this direct stimulation can lead to a photic sneeze which is why we find it easier to sneeze while looking at a bright light.
  
  Section::::Pathophysiology.:Propofol-induced inhibitory suppression.
   Section::::Risks.
  
  Sneezing generally does not present any particular risks to the individual, and is usually more an annoyance than a risk of injury. The fits of sneezing brought about by the photic sneeze reflex can, however, have dangerous implications during certain scenarios and activities, such as operating a vehicle, or while undergoing operations (dental, optical) and having bright lights directed towards the patient's face.
  
  Section::::Risks.:Disease transmission.
   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 18-35% of the human population, it is relatively harmless and not widely studied.
   BULLET::::- Tom Wilson, M.D. (1997) "Why do we sneeze when we look at the sun?" "MadSci Network".
  
  BULLET::::- Robert Sheckley (1956), "Protection," a short story about sneezing
  
  Section::::External links.
  
  BULLET::::- The Origins of Popular Superstitions and Customs – T. Sharper Knowlson (1910), a book that listed many superstitions and customs that are still common today.
  
  BULLET::::- Cold and flu advice (NHS Direct)
  
  BULLET::::- Ancient Sneezing: A Gift from the Gods – Elaine Fantham, Professor of Classics at Princeton on NPR Radio.
  
  BULLET::::- Why do my eyes close every time I sneeze? M.G., Sherborn The Boston Globe
   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.
   The photic sneeze reflex manifests itself in the form of uncontrollable sneezing in response to a stimulus which would not produce a sneeze in people without the trait. The sneezes generally occur in bursts of 1 to 10 sneezes, followed by a refractory period that can be as long as 24 hours.
  
  Section::::Symptoms.:Photic sneezing.
  
  A photic sneeze results from exposure to a bright light and is the most common manifestation of the photic sneeze reflex. This reflex seems to be caused by a change in light intensity rather than by a specific wavelength of light.
   The sun emitted a mid-level solar flare, an M7.9-class, peaking at 4:16 a.m. EDT on June 25, 2015.
  
  Section::::Events.:2015.:November.
  
  In early November 2015, solar flares disrupted the air traffic control system in central and southern Sweden, causing heavy delays for passengers.
  
  Section::::Events.:2016.
  
  Section::::Events.:2016.:December.
  
  A sunspot group originally attributed to the new solar cycle 25 is observed. The sunspot numbers continue to decline.
  
  During 2016, there were 26 days with no sunspots (preliminary numbers).
  
  Section::::Events.:2017.
  
  Section::::Events.:2017.:March.
  
  As of 31 March, preliminary reports indicate there had been 24 days during 2017 on which there were no sunspots.
  
  Section::::Events.:2017.:September.
   Section::::Symptoms.:Sneezing after eating.
   Sneeze
  
  A sneeze, or sternutation, is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth and nose in an explosive, spasmodic involuntary action resulting chiefly from irritation of the nasal mucous membrane. This action allows for mucus to escape through the nasal cavity. Sneezing is possibly linked to sudden exposure to bright light, sudden change (fall) in temperature, breeze of cold air, a particularly full stomach, or viral infection, and can lead to the spread of disease.
   Section::::Risks.:Vehicle operation.
   In Ancient Greece, sneezes were believed to be prophetic signs from the gods. In 401 BC, for instance, the Athenian general Xenophon gave a speech exhorting his fellow soldiers to fight against the Persians. A soldier underscored his conclusion with a sneeze. Thinking that this sneeze was a favorable sign from the gods, the soldiers were impressed. Another divine moment of sneezing for the Greeks occurs in the story of Odysseus. His waiting wife Penelope, hearing Odysseus may be alive, says that he and his son would take revenge on the suitors if he were to return. At that moment, their son sneezes loudly and Penelope laughs with joy, reassured that it is a sign from the gods (Odyssey 17: 541-550). It may be because this belief survived through the centuries, that in certain parts of Greece today, when someone is asserting something and the listener sneezes promptly at the end of the assertion, the former responds "bless you and I am speaking the truth", or "bless you and here is the truth", "γεια σου κι αλήθεια λέω", "ya sou ki alithia leo", or "γεια σου και να κι η αλήθεια", "ya sou ke na ki i alithia"). A similar practice is also followed in India. If either the person just having made a not most obvious statement in Flemish, or some listener sneezes, often one of the listeneners will say "  't is beniesd", literally "It's sneezed upon", as if a proof of truth – usually self-ironically recalling this old superstitious habit, without either suggesting doubt or intending an actual confirmation, but making any apology by the sneezer for the interruption superfluous as the remark is received by smiles.
   "Sunquakes" caused by solar flares were first observed during this cycle. These are running acoustic waves, as opposed to the standing waves that constitute the material of helioseismology. The flare impulse launches these waves from the photosphere, and they arc deeply into the interior of the Sun before refracting back to the surface to appear as faint ripples, expanding radially away from the flare some tens of minutes later. The flare in which these waves were first observed, SOL1996-07-09, occurred more than three years after the last previous major event.
  
  Section::::See also.
  
  BULLET::::- Solar variation
  
  BULLET::::- List of solar cycles
   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.
   Sneezing is also triggered by sinus nerve stimulation caused by nasal congestion and allergies.
  
  The neural regions involved in the sneeze reflex are located in the brainstem along the ventromedial part of the spinal trigeminal nucleus and the adjacent pontine-medullary lateral reticular formation. This region appears to control the epipharyngeal, intrinsic laryngeal and respiratory muscles, and the combined activity of these muscles serve as the basis for the generation of a sneeze.
   The parasympathetic nervous system has many neighboring fibers that respond to different stimuli. When one stimulus activates multiple nerve fibers of the parasympathetic nervous system, parasympathetic generalization is occurring. There is a possibility that sensory input from the eyes could travel to the neurons in the cortex that interpret such signals, but neighboring neurons which are involved in sneezing are also activated, due to the generalization. This could lead to a sneeze in response to a stimulus other than nasal irritation.
  
  Section::::Pathophysiology.:Increased light sensitivity.
   In some cases, patients with episodic SUNCT only exhibit symptoms biannually, in spring and fall. This periodicity suggests that the hypothalamus, which is responsive to day length and photoperiod for regulating circadian and seasonal rhythms, has a role in its triggering.
  
  Section::::Diagnosis.
   Some people may sneeze during the initial phases of sexual arousal. Doctors suspect that the phenomenon might arise from a case of crossed wires in the autonomic nervous system, which regulates a number of functions in the body, including "waking up" the genitals during sexual arousal. The nose, like the genitals, contains erectile tissue. This phenomenon may prepare the vomeronasal organ for increased detection of pheromones.
   As of April 2018, the sun showed signs of a reverse magnetic polarity sunspot appearing and beginning this solar cycle. It is typical during the transition from one cycle to the next to experience a period where sunspots of both polarities exist (during the solar minimum). The polarward reversed polarity sunspots suggest that a transition to cycle 25 is in process. The first Cycle 25 sunspot may have appeared in early April 2018 or even December 2016.
  
  Section::::Predictions.
   Also, there have been a few unorthodox (unusual) causes of solar urticaria. For those susceptible to visible light, white T-shirts may increase the chances of experiencing an outbreak. In one case, doctors found that the white T-shirt absorbed UVA radiation from the sun and transformed it into visible light which caused the reaction. Another patient was being treated with the antibiotic tetracycline for a separate dermatological disorder and broke out in hives when exposed to the sun, the first case to implicate tetracycline as a solar urticaria inducing agent.
   The next day, September 7, an X1.8-class solar flare erupted from sunspot 1283, producing a S1 solar radiation storm. A fourth flare, an M6-class, was ejected by the same sunspot on September 8.
  
  This sequence of flares produced waves of ionization in Earth's upper atmosphere, briefly altering the propagation of low-frequency radio signals around our planet. Moreover, the eruptions hurled clouds of plasma in our direction. CME impacts, strong geomagnetic storms and auroras were registered from September 9 onwards.
  