A sneeze is a convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. Sneezing expels air forcibly from the mouth and nose in an explosive, spasmodic involuntary action resulting chiefly from irritation of the nasal mucous membrane. It may be linked to sudden exposure to bright light, sudden change in temperature, a particularly full stomach, or viral infection, and can lead to the spread of disease.Photograph: James Gathany/Centers for Disease Control and Prevention