Why Do We Sneeze?

Donna Griffiths from Worcestershire, England holds the Guinness book of world records for the longest sneezing fit. The fit began on 13 January 1981 and ended on 15 September 1983 making it a total 978 days. I cannot fathom the relief she might have felt on the 16th of September, 1983.

But why she sneezed for so long the internet failed to tell me, but normal average sneezing, though a curiosity in itself, is explainable. The reason is as simple as this – it is to keep out germs.

woman sneezing

A sneeze can happen because of many reasons, but its ultimate purpose is to protect you.

Reflex

We sneeze for the same reasons we cough. One’s body coughs either when there is something irritating the throat, there is too much mucus, or there is something in the trachea (the windpipe) that shouldn’t be there. Sneezing works the same way too.

Sneezing happens in two parts or phases. The first is the nasal or sensitive phase when something irritating has entered the nose. This irritant, say a dirt particle, enters where it has no business being, the nasal cavity. The nose doesn’t take this breach lying down. Nerve endings in the nose, either directly informed or indirectly by nose hairs, send a signal through a bunch of face nerves called cranial nerve V to the sneeze centre in the medulla oblongata. The medulla oblongata is a small part of the brain located in the brain stem (the area where the brain ends and the spinal cord starts).

Image Caption: These are all the cranial nerves. The Trigeminal nerve, also called cranial nerve V is the nerve that sends impulses from the nose to the brain.

cranial nerves brain

The Medulla’s functions are to keep the body alive. It controls heart rate, breathing rhythm, dilation of blood vessels. Summed up, its job is to control all involuntary movements so that you, the person reading this article, can think about other more important things (like learning how to juggle). The Medulla also plays a role in reflex actions.

We’re all taught in school that the reflex arc does not involve the brain, the spinal cord is enough. In this scenario, the nerves in the nose (cranial nerves V) are closer to the brain than to the spinal cord and end in the medulla oblongata (like a few other cranial nerves).

Once the medulla receives the information of the intruder enough times, it activates the sneeze reflex plan.

This is the second phase, the respiratory phase. The sneeze reflex plan is intricate and precisely timed. The medulla instructs the eyes to close, lungs to take in deep breathes (Ah Ah Ah…), the glottis and vocal cords close, and muscles involved in expiration tighten.

All this leads to a build-up of pressure. When the pressure is high enough, the glottis opens and out comes the sneeze (Achoo!).  The feeling that the heart stops during a sneeze is likely a result of the blood pressure increasing.

respiratory centers of brain

Areas in the medulla that control the physiology of a sneeze.

The unusual sneezes

But people don’t only because of a physical irritant in their nose. There are various curious sneezing related conditions as well.

Photic sneeze reflex or more appropriately called ACHOO syndrome – autosomal compelling helio-ophthalmic outburst syndrome is sneezing brought on by sudden exposure to bright light after the eyes have adapted to the dark. It might affect 17 to 35% of the world’s population.

The name suggests that the syndrome is genetically linked showing autosomal dominant inheritance pattern. This means that the syndrome is a result of one mutant gene and one normal gene on an autosomal pair of chromosomes (non-sex linked chromosome). The mutant gene can express itself over the normal gene, thereby dominating it.

How light stimulates sneezing still remains a question mark. There are many theories out there that talk about different brain centres and nerves being stimulated. But overarching point is the same – somewhere there is an overlap between the pupillary reflex arch (reflex that changes the diameter of the pupil based on the amount of light) and the sneezing reflex arch.

A 2010 study recorded the EEG of 10 photic sneezer with a control group and found that the photic sneezers were more sensitive to light than controls. They also noticed a co-activation of the somatosensory cortex in photic sneezers. They suggest in their paper that the ACHOO syndrome might not follow a classical reflex arch path. The number of participants in this study are small and more work would need to be done to support this.

Though this condition sounds innocuous, Lang and Howland suggest that certain professions are dangerous for photic sneezers such as pilots or high-wire acrobats. Driving through a dark tunnel and emerging out in bright sunlight poses problems as well.

People have also recorded sneezing after eating, called snatiation (a portmanteau of sneezing and satiation, as well as an acronym Sneezing Noncontrollably At a Tune of Indulgence of the Appetite-a Trait Inherited and Ordained to be Named’ (10 points for creativity), and sneezing after sexual intercourse. The reasons and mechanisms for both of these are unknown.

Sneezing and its neurology hasn’t been widely researched. Though modern science is busy with other work (mapping the brain for one), history has some interesting revelations about the significance sneezing has held during different times and in different cultures.

Sneezing has been largely considered in history as a good omen in ancient Greece and Rome, which quickly changed to a bad omen when the black plague hit Europe. It has catalysed action (a sneeze made Athenian soldiers begin their attack on Persia before their commander Xenophone had finished his speech), and has been seen as a holy sign. When the black plague devastated Europe, Pope Gregory VII is reported to have said ‘May God bless you’ when the sick sneeze because that’s all he could do.

So, next time you or someone else sneezes take pleasure in the knowledge that their body is protecting them and say ‘God bless you’ in remembrance of Pope Gregory VII.

References

  1. Library of Congress
  2. A Journal on Sneeze reflex
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About the Author:

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spends a lot of time watching movies, and an awful lot more time discussing them. He likes Harry Potter and the Avengers, and obsesses over how thoroughly Science dictates every aspect of life… in this universe, at least.

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