Why do we sneeze?

The answer

Sneezing is a powerful semi-autonomous reflex designed to clear the nasal passages of irritants, pathogens, and allergens. When particles stimulate trigeminal nerve endings in the nasal mucosa, the signal travels to the sneezing center in the lateral medulla of the brainstem, triggering a coordinated sequence: deep inhalation, buildup of thoracic pressure against a closed glottis, then explosive exhalation that propels mucus and air at speeds exceeding 100 mph (160 km/h). A single sneeze can expel up to 40,000 droplets. Sneezing can also be triggered by bright light in approximately 18 to 35 percent of people, a genetic trait called the photic sneeze reflex (or ACHOO syndrome), believed to result from cross-wiring between the trigeminal nerve and the optic nerve in the brainstem.