Nasal obstruction is blockage of the nose or nasal cavity and can be caused by a wide variety of complications. Most cases are caused by sinusitis, allergies, or the overuse of nasal sprays. The blockage may also be caused by an anatomical factor, such as a deviated septum, enlarged adenoids, nasal polyps (swellings of the nasal and sinus mucous membrane) or foreign bodies in the nose.