For those who are allergically sensitised, the physical process begins when specific proteins in airborne pollen enter the nose as we breathe in. These proteins bind to antibodies -- called immunoglobulin E -- in the bloodstream. When the antibodies attach to mast cells and basophils in the mucous membrane of the nose, the compound histamine and other inflammatory mediators are released.
Histamine irritates nerve cells in the nose, resulting in signals being sent to the brain that trigger a sneeze through the trigeminal nerve network. This pathway controls sensation and movement in the face. The end result is the brain engaging pharyngeal and tracheal muscles to create a large opening of the nasal and oral cavities, followed by a powerful discharge of air and bioparticles.
The whole process serves to purge the body of allergenic particles and proteins that it has ingested. Because histamine sets off this immune system response, nasal and oral antihistamine medications work well by blocking the compound at its sites of action. Nasal corticosteroids also can control sneezing and other nasal allergy symptoms by reducing the amount of inflammation present in the nose at any one time.