The air around us is very polluted. It contains various particles like pollen, dust, smoke, dirt, etc. While breathing, these particles move through the nasal cavity. Our nasal cavity has many small hairs. When we inhale this polluted air, the particles present in the air get trapped by the hairs of the nasal cavity. This trapping of the dirt particles causes unnecessary irritation in the nose. This is the reason why human beings sneeze when they inhale dust-laden air.