Why do we sneeze?

Why do we sneeze?
A sneeze is an involuntary expulsion of air from your mouth and nose.

A sneeze is a semi-autonomous, spastic expulsion of air from the lungs, through the mouth and nose. The main function of a sneeze is to cleanse the nasal cavity, specifically to remove any foreign particles that are lodged in the nasal mucus.

During a sneeze, the soft palate and palatine uvula depress. The back of the tongue rises and then partially closes the passage to the mouth. This ensures that the air will be expelled through the nose, and not the mouth. However, the tongue in only able to partially close the mouth, hence a significant part of the air is expelled through the mouth as well.

A sneeze is mainly caused by an irritant within the nose, usually foreign particles that are irritating the nasal mucous membrane. When the irritants pass through the nasal hairs to reach the nasal mucosa, it causes the release of histamines, which irritate the nerve cells in the nose. This results in a signal being sent to the brain to initiate the sneeze. The brain does so by sending a signal to the muscles which then create a large opening of the nasal and oral cavities, eventually resulting in the sneeze.

In some cases, a sneeze can also be caused by a sudden exposure to bright light, a sudden fall in temperature, a breeze of cold air, a particularly full stomach, a viral infection, or allergies. 

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