Everyone sneezes, be it during allergy season, while having a cold, or when opening a very dusty book. However, most of us don’t understand what is actually happening while we sneeze. All we experience is the snot flying from our noses and mouths and the embarrassment we feel right after.
What exactly is a sneeze?
To sneeze is “to make a sudden violent spasmodic audible expiration of breath through the nose and mouth especially as a reflex act” (1). This sounds like a mouthful- let’s break it down. A sneeze is essentially a fast gust of air coming out of your nose and mouth. The problem with the second part of the definition is that it is not “especially” a reflex act, it is essentially just a reflex. It’s a release of pressure that stops irritation of the epithelium lining (2) and expels unwanted bacteria. So, what causes this reflex?
What Causes Sneezing?
Sneezes are reactions to an anomaly within the respiratory system. The nose is the main tool for breathing air in and out of the lungs. The cavities of the nose are narrow so that the air coming in will speed up and become more turbulent, interacting more with the nasal mucosa, the tissue that lines the nasal cavity (3). This interaction will force the dust particles and bacteria in the air to come in contact with the nasal hairs that cover the nasal mucosa and become trapped within them. When enough particles pass through the nasal hairs and reach the nasal mucosa, the sneeze occurs.
How does sneezing happen?
Once the foreign particles reach the nasal mucosa, it triggers the release of histamine, a chemical that irritates the nerve cells in the nose. These nerve cells are actually the endings of the trigeminal cranial nerve, a major face nerve that is responsible for sensation on the face and the motion of the jaw, such as biting and chewing (4). The irritated nerve cells send an electrical signal that travels up the trigeminal cranial nerve into the medulla oblongata, a part of the brain that is responsible for involuntary actions, and thus sneezing (5). The medulla then sends a signal to close the air passage to the mouth, creating a single channel from the lungs to the nose. The chest expands and the lungs inflate until there is a very great difference in pressure in your body (6). Once there is enough pressure in the lungs, the air shoots out of the nose, fast enough to clear out the bacteria and dust particles that were trapped, together with much of the mucus from the nose. These drops of bacteria and mucus travel out of the body at speeds of up to 100 mph (7). Since the mouth cannot be completely shut, some of the air and mucus comes out of the mouth as well.
More about sneezing
Unlike coughing, sneezing is completely involuntary. You can cough on command, but you cannot sneeze on command.
Go ahead. Try to sneeze.
This makes it very hard to study, because it is unconscious and infrequent and therefore it is hard to collect data for (8). However, there are a few things that we do know about it, and more studies are constantly being performed.
It is impossible to sneeze while sleeping because of REM atonia, which paralyzes the body when it is asleep. This means that the motor neurons cannot be stimulated, and therefore no reflex signals are relayed to the brain.
Can your eyes pop out if they remain open?
Most people’s eyelids close when they sneeze. This leads many people to the conclusion that it is a defense mechanism that would stop your eyes from flying out of your head. However, this is not the case. Both the eyes and the nose are connected by the aforementioned trigeminal nerve. When the nerve sends signals down for the sneeze, it also contracts the muscles in the eyes and forces the eyelids to close. Therefore, the eyelids closing is just a side effect of the sneezing, and there is no danger of your eyes popping out (9).
Many people think that sneezing is impolite or distracting, especially in a professional setting, such as meetings. However, attempting to suppress a sneeze is very unhealthy and potentially dangerous.
Since there is a large pressure buildup in the lungs before a sneeze, this pressure needs to be released somewhere. If you close your nose, the air will not be able to come out of it, and therefore it will be released in places it was not intended to be in. Take the case of a man in England who was hospitalized after a sneeze. He had attempted to suppress it, and therefore the air was released into his tissue and seeped into it. The pressure had also caused a rupture in his pharynx, a region of the throat. He was fed intravenously and was thankfully released after 7 days (10). The moral of the story is that although sneezes may seem unnecessary and eve disrupting, they are a natural phenomenon of the body, which should be allowed to go to completion.
If you have learned nothing else, just remember to sneeze and let sneeze.
References and Footnotes:
(2) A type of animal tissue that lines the inside of the nose