Sinuses are hollow air spaces situated in the skull, which are present below the cheeks , at the root of the noseand at the region where both the eyebrows . Since the sinus are like hollow spaces in the skull filled with air, they help the skull to be light, humidify the air and helps in enhancing our voice. Conditions that can cause sinus blockage include, The common cold, Allergic rhinitis, which is swelling of the lining of the nose, Small growths in the lining of the nose called nasal polyps, A deviated septum, which is a shift in the nasal cavity.