sneeze

A sneeze is the nose's version of a cough: a sudden, forceful burst of air that mainly blasts out through the nostrils to expel irritants from the upper airway. Where a cough clears the throat and chest, a sneeze clears the nose and the back of the nasal passages.

It begins when something tickles the lining of the nose — dust, pepper, pollen, a virus, or even bright light in some people. Nerves carry that irritation to a sneeze center in the brainstem, which orchestrates a deep breath, closure then sudden opening of the upper airway, and a powerful squeeze of the chest muscles. The result is an explosive jet that carries droplets and trapped particles outward at high speed.

As a protective reflex, sneezing helps keep the entrance to the respiratory tract clear. The same droplet spray that ejects irritants, however, also broadcasts respiratory viruses to the surrounding air, which is why sneezes are a major route of spread for colds, influenza, and similar infections, and why covering a sneeze matters.