Upper Respiratory Tract Infection (URTI): This is the most common cause of blocked ears and sinus, often resulting from a viral infection that leads to inflammation and congestion of the nasal passages and Eustachian tubes, which connect the middle ear to the back of the nose and throat.

Allergic Rhinitis: Allergies can cause nasal congestion, sinus pressure, and Eustachian tube dysfunction, leading to blocked ears.
Sinusitis: Inflammation or infection of the sinuses can cause pain, pressure, and congestion, which may also affect the ears due to the shared drainage pathways.
Eustachian Tube Dysfunction: This condition, where the tube that regulates air pressure in the ears doesn't open and close properly, can lead to a feeling of blocked ears and can be associated with sinus issues due to the anatomical connection.

Mastoiditis: An infection of the mastoid bone in the skull, which can spread from the middle ear. It's a serious condition that requires prompt treatment to prevent complications.
Cavernous Sinus Thrombosis: A rare but potentially life-threatening condition where a blood clot forms in the cavernous sinus, which can be a complication of sinusitis or other facial infections.
Nasal Tumors: Although rare, tumors in the nasal cavity or sinuses can cause blockage and pressure, potentially leading to symptoms of blocked ears and sinus.

Relapsing Polychondritis: A rare autoimmune disorder that can cause inflammation of the cartilage in the ears, nose, and trachea, potentially leading to symptoms of blocked ears and sinus.
Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A rare autoimmune disorder that can cause inflammation of the blood vessels and affect various parts of the body, including the sinuses and ears.
Eosinophilic Otitis Media: A rare condition characterized by the accumulation of eosinophils in the middle ear, often associated with allergies or asthma, which can cause symptoms of blocked ears.