Sneezing can spread disease by launching disease vectors into the air
|Biological system||Respiratory system|
|Stimuli||Irritants of the nasal mucosa
|Method||Expulsion of air through nose|
|Outcome||Removal of irritant|
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. 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.
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The function of sneezing is to expel mucus containing foreign particles or irritants and cleanse the nasal cavity. During a sneeze, the soft palate and palatine uvula depress while the back of the tongue elevates to partially close the passage to the mouth so that air ejected from the lungs may be expelled through the nose. Because the closing of the mouth is partial, a considerable amount of this air is usually also expelled from the mouth. The force and extent of the expulsion of the air through the nose varies.
Sneezing typically occurs when foreign particles or sufficient external stimulants pass through the nasal hairs to reach the nasal mucosa. This triggers the release of histamines, which irritate the nerve cells in the nose, resulting in signals being sent to the brain to initiate the sneeze through the trigeminal nerve network. The brain then relates this initial signal, activates the pharyngeal and tracheal muscles and creates a large opening of the nasal and oral cavities, resulting in a powerful release of air and bioparticles. The powerful nature of a sneeze is attributed to its involvement of numerous organs of the upper body – it is a reflexive response involving the face, throat, and chest muscles. Sneezing is also triggered by sinus nerve stimulation caused by nasal congestion and allergies.
The neural regions involved in the sneeze reflex is 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 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. 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 a medical disorder passed along genetically as an autosomal dominant trait.
Sneezing cannot occur during sleep due to REM atonia - a bodily state wherein motor neurons are not stimulated and reflex signals are not relayed to the brain. Sufficient external stimulants, however, may cause a person to wake from their sleep for the purpose of sneezing, although any sneezing occurring afterwards would take place with a partially awake status at minimum.
While generally harmless in healthy individuals, sneezes spread disease through the infectious aerosol droplets, commonly ranging from 0.5 to 5 µm. 40,000 droplets can be produced by a sneeze. To reduce the possibility of thus spreading disease (such as the flu), one should hold the forearm or the inside of the elbow in front of one's mouth and nose when sneezing. Using one's hand for that purpose is inappropriate, since it promotes spreading germs through commonly touched objects (most notably doorknobs).
Preventive measures 
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.
Proven methods to reduce sneezing generally advocate reducing interaction with irritants, such as keeping pets out of the house to avoid animal dander; ensuring the timely and continuous removal of dirt and dust particles through proper housekeeping; replacing filters for furnaces and air-handling units; air filtration devices and humidifiers; and staying away from industrial and agricultural zones. Some people, however, find sneezes to be pleasurable and would not want to prevent them.
Historic instances and practices 
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" (in Greek "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).
In Europe, principally around the early Middle Ages, it was believed that one's life was in fact tied to one's breath - a belief reflected in the word "expire" (originally meaning "to exhale") gaining the additional meaning of "to come to an end" or "to die". This connection, coupled with the significant amount of breath expelled from the body during a sneeze, had likely led people to believe that sneezing could easily be fatal. This theory, if proven conclusively, could in turn explain the reasoning behind the traditional "God bless you" response to a sneeze, the origins of which are currently unclear. (see "Traditional Responses To A Sneeze" below for alternative explanations). Sir Raymond Henry Payne Crawfurd, for instance, the late registrar of the Royal College of Physicians, in his 1909 book "The Last Days of Charles II", states that, when the controversial monarch was on his deathbed, his medical attendants administered a concoction of cowslips and extract of ammonia to promote sneezing. However, it is not known if this promotion of sneezing was done to hasten his death (as coup de grace), or as an ultimate attempt at treatment.
In certain parts of Eastern Asia, particularly in Chinese culture, Japanese culture and Vietnamese culture, a sneeze without an obvious cause was generally perceived as a sign that someone was talking about the sneezer at that very moment. This can be seen in the Book of Songs (a collection of Chinese poems) in ancient China as early as 1000 BC, and this belief is still depicted in present-day manga and anime. In China, Vietnam and Japan, for instance, there is a superstition that if talking behind someone's back causes the person being talked about to sneeze; as such, the sneezer can tell if something good is being said (one sneeze), something bad is being said (two sneezes in a row), even if someone is in love with them (three sneezes in a row) or if this is a sign that they are about to catch a cold (multiple sneezes).
Parallel beliefs are known to exist around the world, particularly in contemporary Greek, Slavic, Celtic, English, French, and Indian cultures. Similarly, in Nepal, sneezers are believed to be remembered by someone at that particular moment.
In Indian culture, especially in northern parts of India, and also in Iran, it has been a common superstition that a sneeze taking place before the start of any work was a sign of impending bad interruption. It was thus customary to pause in order to drink water or break any work rhythm before resuming the job at hand in order to prevent any misfortune from occurring.
Contrarily, in Polish culture, especially in their borderlands, the Kresy, a popular belief persists that sneezes may be an inauspicious sign that one's mother-in-law speaks ill of their son-in-law at that moment. The same phenomenon is thought to correspond to daughters-in-law and their mothers-in-law. As with other Catholic countries, such as Mexico, Italy, or Ireland, the remnants of pagan culture are fostered in Polish peasant idiosyncratic superstitions.
The practice among Islamic culture, in turn, has largely been based on various Prophetic traditions and the teachings of Muhammad. An example of this is Al-Bukhaari's narrations from Abu Hurayrah that the Islamic prophet once said:
When one of you sneezes, let him say, "Al-hamdu-Lillah" (Praise be to God), and let his brother or companion say to him, "Yarhamuk Allah" (May God have mercy on you). If he says, "Yarhamuk-Allah", then let [the sneezer] say, "Yahdeekum Allah wa yuslihu baalakum" (May God guide you and rectify your condition).
Common verbal responses to a sneeze 
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In English-speaking countries, the common verbal response to another person's sneeze is "(God) bless you" or the much less common "Gesundheit" (the German word for "health") or "Salud" (the Spanish word for "health"). There are several proposed origins for the use "bless you" or "god bless you" in the context of sneezing:
- Various alleged but conflicting superstitions relating the sneeze to evil spirits. This includes beliefs that a sneeze could release one's soul, thus leading to its possible capture by lurking evil spirits (as explained in the "Historic instances and practices" section above), or that the evil spirits could enter the body through the open mouth of a sneezing individual, or that the individual is sneezing out sins or evil spirits which had taken residence within the body and is thus in need of the blessing to prevent the exorcised spirits from re-entering the body.
- Some say it came into use during the plague pandemics of the 14th century. Blessing the individual after showing such a symptom was thought to prevent possible impending death due to the lethal disease.
- In Renaissance times a superstition was formed claiming one's heart stopped for a very brief moment during the sneeze, saying bless you was a sign of prayer that the heart wouldn't fail.
- It has also been stated that one says "(God) bless you" so that one does not catch the flu, cold, or any other forms of sickness.
- Indian culture is to respond with Krishna, similar to a blessing in western cultures.
- In the Telugu culture, a rather uncommon reciprocation to someone's sneeze is 'chiranjeeva'(చిర౦జీవ)which means 'may you live long' (from Sanskrit).
Achoo is the English onomatopoeia for the sound made during sneezing.
See also 
|Wikimedia Commons has media related to: Sneeze|
- "Sneeze". Retrieved April,06, 2012.
- Nonaka, S.; T. Unno, Y. Ohta, S. Mori (19 March 1990). "Sneeze-evoking region within the brainstem". Brain Research (Elsevier B.V.) 511 (2): 265–270. doi:10.1016/0006-8993(90)90171-7. Retrieved 7 February 2013.
- "Myth: Can sneezing with your eyes open make your eyeballs pop out?".
- Breitenbach, RA; Swisher PK, Kim MK, Patel BS (December 1993). The photic sneeze reflex as a risk factor to combat pilots.. 927th USAFR Clinic, Selfridge Air National Guard Base, MI 48045-5046: PubMed. PMID 8108024. Retrieved 7 February 2013.
- "A Moment of Science: Sleep On, Sneeze Not". Retrieved 2008-11-14.
- Cole EC, Cook CE. Characterization of infectious aerosols in health care facilities: an aid to effective engineering controls and preventive strategies. Am k Infect Control. 1998 Aug;26(4):453-64. Sneezing can transmit many diseases PMID 9721404
- Adkinson NF Jr. (2003). "Middleton’s Allergy: Principles and Practice.". Phytomedicine. (6 ed.).
- Wylie, A, (1927). "Rhinology and laryngology in literature and Folk-Lore". The Journal of Laryngology & Otology 42 (2): 81–87. doi:10.1017/S0022215100029959.
- 《詩經·終風》 「寤言不寐，願言則嚏」
- Ancient Sneezing: A Gift from the Gods - Elaine Fantham, Professor of Classics at Princeton on NPR Radio.
- Why do my eyes close every time I sneeze? M.G., Sherborn The Boston Globe
Further reading 
- Cecil Adams (1987). "If you hold your eyelids open while sneezing, will your eyes pop out?". The Straight Dope.
- Barbara Mikkelson (2001). "Bless You!" Urban Legends Reference Pages.
- Tom Wilson, M.D. (1997) "Why do we sneeze when we look at the sun?" MadSci Network.
- Robert Sheckley (1956), "Protection," a short story about sneezing
|Look up sneeze in Wiktionary, the free dictionary.|
- The Origins of Popular Superstitions and Customs - T. Sharper Knowlson (1910), a book that listed many superstitions and customs that are still common today.
- Cold and flu advice (NHS Direct)