Sneezing may be due to insufficient stimulation of the nasal cavity or insufficient muscle contraction. Sneezing is a protective reflex of the nasal cavity, the trigeminal nerve endings in the nose are stimulated by such as dust, odor, cold air, etc., through the nerve reflex, starting with a deep inhalation, followed by a rapid and forceful exhalation; accompanied by a drop in the uvula, tongue pressure to the soft palate, resulting in a strong, sudden airflow will be stimulated by the spray out. The effect is to expel foreign bodies or excessive secretions from the upper airway. If the nasal cavity is not stimulated enough, or the muscle contraction is not strong enough, resulting in the descent of the uvula, tongue downward pressure is not strong enough, will produce the phenomenon of wanting to sneeze but can not sneeze out.