Why do we sneeze? A study

Sneezing is one of the ways the body expels harmful substances. A sneeze is caused by spasms within the chest and pharynx (the part that connects the nasal cavity and oesophagus). Whenever something irritates the nerve endings in your nose, they send a message to the brain to get rid of the substance. 

The brain then sends signals to the chest cavity (to squeeze the lungs) and the pharynx (to prevent air expulsion through the mouth). The result? A sharp burst of air via the nose - aka a sneeze!