(1) Sneezing expels the dust particles from the inhaled air so that only clean air enters our body.
(2) When we inhale dust-laden air, the dust irritates the nose; as a reflexive action, dust is thrown out through sneezing.
(3) When we inhale air containing dust particles, the particles get trapped in the hair present in nostrils.
(4) Sometimes, these particles may pass through the hair and enter the nasal cavity. They irritate the mucus lining of the nasal cavity, and as a result we sneeze.