Sneezing is widely considered to be an agent of disease dissemination in many cultures.

Biological elements

The function of sneezing is the expulsion of mucus from the nose containing foreign particles or irritants as well as the cleansing of the entire sinus cavity during colds and other viral infections. During a sneeze the soft palate and uvula depress while the back of the tongue elevates to partially close off the passage to the mouth so that air ejected from the lungs may be expelled through the nose. Because the closing off 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 widely from one individual to another, but the mechanics of a sneeze as outlined above assure that it will function toward this end.

Overall mechanism

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 reason behind the particularly powerful nature of a sneeze is attributed to its involvement of not simply the nose and mouth, but numerous organs of the upper body – it is a reflectory response that involves the muscles of the face, throat, and chest.

An alternative cause of sternutation is sudden exposure to bright light - a bodily attribute known as the photic sneeze reflex. Up to 37 percent of individuals are believed to have this particular genetic traitFact: date=June 2008, which is most commonly related to exposure to direct sunlight.

A rarer alternative 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 that would occur afterwards would take place with at least a partially awake state of mind.

Epidemiology

While generally harmless in healthy individuals, sneezes are capable of spreading disease through the potentially infectious aerosol droplets that they can expel, which commonly range from 0.5 to 5 µm in diameter. About 40,000 such droplets can be produced by a single sneeze.