Sneezes and Sneezing: Causes, Facts, Myths, and Mysteries
A Useful and Slightly Mysterious Behaviour
Sneezing is a brief but explosive process that is very effective at moving irritating material out of the nose. The process can be sudden, surprising, embarrassing, and annoying. It can also be very inconvenient, especially when it occurs frequently. Most of us are temporarily helpless while we sneeze. Despite these problems, sneezing is an interesting phenomenon.
The medical term for sneezing is sternutation. Many different factors can stimulate sternutation, including infections and allergies, inhaled irritants, a sudden exposure to bright sunlight or a cold temperature, and a stomach that is very full of food. The process is still slightly mysterious, even for scientists. Most people no longer believe that a sneeze represents a soul leaving the body as some people in the past thought, but myths about sternutation still exist.
Humans aren't the only organisms that sneeze. Other mammals also perform the behaviour, and so do birds and some reptiles.
Why Do We Close Our Eyes When We Sneeze?
Do we close our eyes when we sneeze to stop our eyeballs from popping out due to the force that's created, as some people claim? Researchers say that this is very unlikely. In fact, some people are able to sneeze with their eyes open (although this is very difficult to do) and their eyeballs stay in place. There may be a slight increase in blood pressure behind the eyes during a sneeze, but it's not enough to push the eyeballs out.
Perhaps closing our eyes prevents bacteria and fluid from entering the eyes during the sneeze? Most researchers consider this to be unlikely too, since the fluid and particles from the nose are propelled away from our bodies when we sneeze, sometimes for long distances.
The most likely explanation is that closing our eyes while sneezing is part of a strong reflex action, just as our lower leg moves involuntarily when the knee is tapped in a particular place. Some people with stress incontinence release urine when they sneeze. This is thought to be part of the reflex. It may seem unsatisfying to think that the phenomenon of closing the eyes while sneezing has no purpose, but that's the current belief of researchers.
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The Mechanics of Sneezing
The lining of the nostrils is called the nasal mucosa. When the mucosa is stimulated by an irritation, nerves in the nose send signals to the sneeze centre of the brain. This centre is located in the medulla oblongata at the base of the brain. We don't control this area of the brain consciously.
During a sneeze, the medulla oblongata sends signals to the chest and throat muscles and also signals the eyes to shut. The tongue presses against the roof of the mouth. The person takes a deep breath and mucus is forcefully expelled out of the nose and saliva out of the mouth. Chest and stomach muscles contract to help the expulsion.
An average sneeze lasts between two and three seconds and can't be stopped once it has begun. Some people always sneeze more than once. This seems to be due to individual variations in the sneeze reflex.
What Makes Us Sneeze?
The nasal mucosa may be irritated by particles that enter the nostrils from the outer or inner environment, such as dust, pollen, pet hair, pepper, or fluid. Allergies may also lead to mucosal irritation. A chemical called histamine is released from certain cells in the body during an allergic reaction. Histamine causes inflammation and swelling of the nasal mucosa. The mucosa also swells when we have a cold. A swollen mucosa is very sensitive to irritation.
In some people the sneeze reflex can also be produced by other factors, such as overfilling the stomach or entering bright sunlight after being in a darker building. Some people sneeze when they pluck their eyebrows or when they are exposed to cold air or strong odours. Emotional arousal may trigger sneezing in certain people. Sometimes the process is related to an epileptic seizure.
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Sternutation in Bright Sunlight
Sneezing in bright sunlight is known as a photic sneeze or the ACHOO syndrome (Autosomal-Dominant Compelling Helio-Ophthalmic Outburst Syndrome). The term was created by scientists having some fun, since the sneeze is often thought to have no effect on a person's life. However, experiencing a photic sneeze while driving a vehicle could have serious consequences if the eyes close. It's important that people who experience the sneeze wear sunglasses if they're driving on a sunny day.
Between 20% and 35% of the population experience photic sneezes. The phenomenon has a genetic basis.
The Eye and the Optic Nerve
An error in the transfer of information through the optic nerve seems to be the basis of a photic sneeze. Information from the retina of our eyes travels along the optic nerve to the brain, which creates an image. The retina is the light-sensitive layer at the back of the eye. The optic nerve also triggers the brain to constrict the pupil in bright light to prevent the light from damaging the retina. The pupil is the round opening in the centre of the iris (the coloured part of the eye) that enables light to enter the eyeball.
How Does a Photic Sneeze Occur?
A nerve called the trigeminal nerve is located close to the optic nerve. The trigeminal nerve detects stimuli on the face, including the nose, and sends the information to the brain. It has several branches.
When people who experience photic sneezes enter bright sunlight, it's thought that an error is made in nerve conduction. As the optic nerve is transmitting a signal to the brain to "tell" it that the sunlight is strong and potentially irritating, some of the signal is believed to cross over into the nearby trigeminal nerve. When the brain receives the signal from the trigeminal nerve it responds as though the nose has been irritated and causes a sneeze.
A branch of the trigeminal nerve goes to the eyebrows. Plucking the eyebrows may trick the brain into thinking that the nose has been stimulated and trigger it to produce the sneeze reflex.
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Questions About Sneezing
How Fast Does a Sneeze Travel?
It's commonly claimed that sneezes travel at up to 100 miles an hour. This claim originated many years ago and hasn't been confirmed by recent research. It may be incorrect. An investigation performed by a virologist at the Alberta Provincial Laboratory for Public Health found that sneezes travel at 10 miles an hour. The scientist said that his subjects were small framed and that the results may have been different with subjects who had a larger frame. The popular Mythbusters TV show found that one person's sneeze travelled at 35 miles an hour and another person's at 39 miles an hour.
Does Our Heart Stop When We Sneeze?
This is another common myth. It's true that as we sneeze our chest muscles contract. This may momentarily change the rhythm of the heart beat, but it doesn't stop the heart from beating.
Is Sneezing Dangerous?
Sneezing is rarely dangerous and is at worst an annoyance and a nuisance for most people. Sometimes, though, it can cause problems. Sneezing while driving a vehicle is potentially dangerous because it causes us to close our eyes. In addition, sneezing can spread pathogens (organisms that cause disease), which is dangerous for other people. Very rarely, in susceptible people a sneeze can cause a stroke or break bones.
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Some More Questions and Answers
Can We Sneeze in Our Sleep?
No, say the experts. When we are asleep the nerves involved in the sneeze reflex are unable to create the reflex. The reflex pathway is "sleeping", too.
What is Snatiation?
Sneezing caused by an overfull stomach is genetically controlled and is sometimes known as snatiation—Sneezing Non-controllably at a Time of Indulgence of the Appetite—a Trait Inherited and Ordained to be Named. The idea for the name came from the combining of the words sneeze and satiation.
Why Do People Say "Bless You" after a Sneeze?
There are several theories that try to explain how this tradition began, but it's not certain which is correct. It may have begun during the bubonic plague. Sneezing is one of the symptoms of the plague, so perhaps this saying was an attempt to protect the sufferer from death. Other theories suggest that the saying began because people thought that a sneeze could expel the soul from the body, or they believed that it was a sign of a demon leaving the body.
Why Do People Say "Gesundheit" after a Sneeze?
The word gesund is German for healthy. The suffix heit is equivalent to the suffix ness in English. When someone says "Gesundheit" to a sneezer, they are wishing them health and hoping that the person isn't ill (or at least this was the original meaning of the term).
One More Question: What Was the Longest Sneezing Fit Ever?
Donna Griffiths from England sneezed for 978 days in a row. She began sneezing on January 13th, 1981, and stopped sneezing on September 16th, 1983. Her sneezes occurred every minute to start with and then slowed to one every five minutes. She holds the Guinness World Record for her "achievement".
Sneezing has an amusing aspect, but it can also be annoying, as I'm sure it was for Donna Griffiths. It's interesting that even today there are some unanswered and puzzling questions about the process.
© 2012 Linda Crampton