During normal sleep the tone of the pharyngeal airway dilator muscles is decreased resulting in upper airway narrowing and increased resistance to airflow. Nasal obstruction may result from a variety of anatomical abnormalities such as septal deviation, nasal polyps, adenoid hypertrophy and rhinitis such as allergic rhinitis, acute viral rhinitis, vasomotor rhinitis and non-allergic rhinitis with nasal eosinophilia syndrome. Disordered breathing during sleep can both result from and be worsened by nasal obstruction. In children, nasal obstruction due to enlarged tonsils and adenoids results in a switch to oral breathing which may lead to the adenoid faces because of changes in the craniofacial structures during growth that predispose to disordered breathing during sleep.