Sneezing is something that we have all experienced, regularly in our lives. It is a process that the body uses to expel unwanted material from the nasal passages that might have gotten caught up there. It is a reflux response and cannot be voluntarily carried out. It is similar to coughing, although coughing can be consciously done, where sneezing cant. Sneezing is basically a defense method the body uses to prevent infections from passing through the nasal canals and entering the rest of the body, where damage could be caused.
Sneezing itself is a violent explosion of nasal mucus and other particles which have become lodges there. It has been recorded as being at around 95 mph, which is too fast for us to see usually. The force of the sneeze means that we close our eyes to prevent them from being covered in the mucus that we spray out. But also because the pressure expelled by sneezing could in theory damage the eyes if they were open. As well as this the body uses closing the eyes as a response when something unexpected is happening, in case the body is about to be struck.
The mucus in the nose has the function of protecting the inner nasal passages from any particles in the air being taken into the lungs. When we breathe there are millions of dust particles and other organic materials such as pollen that we breathe in. The mucus in the nose acts as a sticky barrier to this, and stops anything from traveling any further inside the body. Most of these particles will stay there until they are either dissolved in the nasal mucus, or they are expelled by us blowing our noses or sneezing.
A small percentage of the things that we breathe in cause irritation to the inside of the nose. This can be because they are actually harmful, or an allergic reaction is taking place. An allergic reaction is basically caused by the body being overly sensitive to often harmless substances. The body thinks it is under attack, when really the substance is harmless to most people. From here the body tries to expel whatever is causing the irritation. In other parts of the body it will send antibodies to remove the unwanted molecules, however in the nose, it has a more effective method.
Many people have allergic reactions to one thing their entire lives. Hay-fever is a very common one for example, where the sufferer is allergic to certain kinds of pollen in the air. Around summer time the reactions from the body cause the sufferer to sneeze constantly, and the eyes to itch, as the body perceives that it is under attack. In reality of course he pollen is harmless and inanimate anyway. Antihistamines can dull the bodies reactions to these stimuli, and mean that you wont suffer from the allergic reactions as much after taking them.
It is then that a sneeze is caused. A sneeze is a rapid exhalation of air from the lungs through the nose. The exhalation gathers speed as it goes through the throat and up through the nasal passages. Because the nasal passages are a lot smaller then the lungs or throat, a high pressure is created which is what gives a sneeze its force. When this high pressure reaches the nasal passages, then the resulting effect looks similar to an explosion that you might see from a cannon. A natural reaction in fact is to arch the head back when sneezing, which helps to inhale the air needed for the sneeze faster. And also gives the resultant sneeze a better starting trajectory in the air, making it travel farther.
As the air pressure in the nose builds as the air is forced out,it sprays the mucus and the offending particles out of the nose and away from the body. The mucus is thrown with such force that a lot of it becomes liquid droplets, which can spread themselves out into over 40,000 separate pieces. This can of course spread the germs to other people if you sneeze on them, which is how some bacteria spread from one person to another and continue to survive.