question: How does looking at a bright light help with sneezing?
comment: It can trigger what's called the photic sneeze reflex. This reflex makes some people sneeze when they look at bright lights. The exact mechanism by which it works isn't fully understood. It's also genetic, so only people with the gene for it will have that reflex.
passages: 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::::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.
   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.
   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.
   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 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.
   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.
   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.
   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.
   Section::::Risks.:Vehicle operation.
   The sneeze reflex involves contraction of a number of different muscles and muscle groups throughout the body, typically including the eyelids. The common suggestion that it is impossible to sneeze with one's eyes open is, however, inaccurate. Other than irritating foreign particles, allergies or possible illness, another stimulus is sudden exposure to bright light – a condition known as photic sneeze reflex (PSR). Walking out of a dark building into sunshine may trigger PSR, or the ACHOO (autosomal dominant compulsive helio-ophthalmic outbursts of sneezing) syndrome as it's also called. The tendency to sneeze upon exposure to bright light is an autosomal dominant trait and affects 18-35% of the human population. A rarer trigger, observed in some individuals, is the fullness of the stomach immediately after a large meal. This is known as snatiation and is regarded as a medical disorder passed along genetically as an autosomal dominant trait.
   Examples of preventive techniques are: the deep exhalation of the air in the lungs that would otherwise be used in the act of sneezing, holding the breath in while counting to ten or gently pinching the bridge of the nose for several seconds.
   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
   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.
   BULLET::::- The inner-ear condition Ménière's disease can be aggravated by flicker. Sufferers of vertigo are recommended to not use fluorescent lights.
  
  BULLET::::- Polymorphous light eruption is a condition affecting the skin thought to be caused by an adverse reaction to ultraviolet light. Its prevalence across Europe is 10-20% of the population. Artificial light sources may provoke the condition, and compact fluorescent light have been shown to produce an eruption.
   Other strategies for relieving photophobia include the use of tinted contact lenses and/or the use of prescription eye drops that constrict the pupil, thus reducing the amount of light entering the eye. Such strategies may be limited by the amount of light needed for proper vision under given conditions, however. Dilating drops may also help relieve eye pain from muscle spasms or seizure triggered by lighting/migraine, allowing a person to "ride out the migraine" in a dark or dim room. A paper by Stringham and Hammond, published in the "Journal of Food Science", reviews studies of effects of consuming Lutein and Zeaxanthin on visual performance, and notes a decrease in sensitivity to glare.
   Section::::Symptoms.:Sneezing after eating.
   Section::::Techniques.
  
  Section::::Techniques.:Photodynamic therapy.
  
  Photodynamic therapy is a form of phototherapy using nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells
  
  One of the treatments is using blue light with aminolevulinic acid for the treatment of actinic keratosis. This is not a U.S. FDA-approved treatment for acne vulgaris.
  
  Section::::Techniques.:Light boxes.
   Section::::Risks.:Medical procedures.
  
  Uncontrollable fits of sneezing are common in patients under propofol sedation who undergo periocular or retrobulbar injection. A sneeze by a sedated patient often occurs upon insertion of a needle into or around their eye. The violent and uncontrollable movement of the head during a reflexive sneeze has potential to cause damage within the patient's eye if the needle is not removed before the sneeze occurs.
  
  Section::::Pathophysiology.
   Several researchers have reported that pranayama techniques are beneficial in treating a range of stress-related disorders. A Cochrane systematic review on the symptomatic relief of asthma by breathing exercises did not find a statistically significant improvement but did find that there was a statistically significant increase in the dose of histamine needed to provoke a 20% reduction in FEV1 (PD20) during pranayama breathing but not with the placebo device.
  
  Section::::Medical.:Risks.
   This form of treatment is meant to reduce the intensity or altogether eliminate the allergic reactions people have by gradually increasing exposure to the form of radiation that brings about the reaction. In the case of solar urticaria, phototherapy and photochemotherapy are the two major desensitization treatments.
  
  Phototherapy can be used for prevention. Exposure to a certain form of light or UV radiation enables the patient to build up a tolerance and outbreaks can be reduced. This type of treatment is generally conducted in the spring. However, the benefits of this therapy only last for two to three days.
   The most widely available method of administering phototherapy to those exhibiting symptoms of SAD is through a light therapy box, which is a commercially available device designed to emit light of a brightness and colour temperature similar to sunlight. Modern devices most frequently use light emitting diodes in either a light box format or alternatively in the form of a wearable device resembling a visor or glasses. Devices that emit blue enriched white light or devices emitting only blue, only green, or a combination of blue and green wavelengths have been found as the most effective in treating SAD.
   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.
   Section::::Related practices.:Prevalence.
   There is much debate about the true cause and mechanism of the sneezing fits brought about by the photic sneeze reflex. Sneezing occurs in response to irritation in the nasal cavity, which results in an afferent nerve fiber signal propagating through the ophthalmic and maxillary branches of the trigeminal nerve to the trigeminal nerve nuclei in the brainstem. The signal is interpreted in the trigeminal nerve nuclei, and an efferent nerve fiber signal goes to different parts of the body, such as mucous glands and the thoracic diaphragm, thus producing a sneeze. The most obvious difference between a normal sneeze and a photic sneeze is the stimulus: normal sneezes occur due to irritation in the nasal cavity, while the photic sneeze can result from a wide variety of stimuli. Some theories are below. There is also a genetic factor that increases the probability of photic sneeze reflex. The C allele on the rs10427255 SNP is particularly implicated in this although the mechanism is unknown by which this gene increases the probability of this response.
  
raw_presuppositions: Looking at a bright light helps with sneezing.
raw_corrections: Some people sneeze when they look at bright lights-photic sneeze reflex.