Middle Ear Effusion: This is a common cause of unilateral hearing loss, often due to Eustachian tube dysfunction, leading to fluid accumulation in the middle ear. It's frequently seen in children but can also occur in adults.

Cerumen Impaction: Buildup of earwax can cause a blockage in the ear canal, leading to unilateral hearing loss. This condition is easily treatable with earwax removal.
Otosclerosis: A condition where abnormal bone growth in the middle ear causes hearing loss. It often starts unilaterally and can progress to the other ear.
Meniere's Disease: Although it can affect both ears, Meniere's disease often starts with unilateral symptoms, including hearing loss, vertigo, and tinnitus.
Acoustic Neuroma: A benign tumor on the nerve connecting the inner ear to the brain, which can cause unilateral hearing loss, tinnitus, and balance problems.

Stroke or Cerebrovascular Accident: While less common, a stroke affecting the auditory pathways can cause sudden unilateral hearing loss. Prompt recognition and treatment are crucial.
Multiple Sclerosis: This autoimmune disease can affect the central nervous system, including areas responsible for hearing, leading to unilateral hearing loss among other symptoms.
Meningioma: A tumor arising from the meninges, which can compress the auditory nerve, leading to unilateral hearing loss.

Ototoxicity: Certain medications or chemicals can cause damage to the inner ear, leading to unilateral hearing loss if the exposure is asymmetrical.
Labyrinthitis: Inflammation of the inner ear, which can be caused by infection or other factors, leading to unilateral hearing loss, vertigo, and tinnitus.
Cholesteatoma: A type of skin cyst in the middle ear that can cause destruction of the surrounding bone and tissue, leading to hearing loss.
Temporal Bone Fracture: Trauma to the temporal bone can cause unilateral hearing loss, among other complications like facial paralysis.