Answer:
so many dust particles are there in the air. during inhalation, those particles fail to reach our lungs due to the presence of ciliated mucous lining in our upper respiratory tract.
primarily nose and its ciliated mucous lining and nasal hair prevent the dust particle to come inside. if some particles get entry then the person starts sneezing until those particles are out.
if the nose fails to prevent the dust then our respiratory tract does it.