Sometimes when we inhale air enriched with dust particles, the hair present in our nostrils trapped those particles.
When these particles anyhow pass through nostril hairs and enter the nasal cavity, they start causing irritation by reaching the mucus lining.
It results in sending the message to the brain.
Brain gives instruction to the nostril to sneeze and remove that foreign particle.
Final Answer
Hence, sneezing is a powerful defence mechanism of our body by which unwanted particles during inhalation are thrown out of the body.