A series of articles by various writers on medical topics this one is by Edel Rooney.
For sound to reach the inner ear it has to travel through the external ear canal, cross the middle ear then enter the hearing organ (the cochlea) in the inner ear.
Anything that blocks this will cause deafness. The commonest blockage is earwax, which can easily be dissolved.
In conductive hearing loss, the second most common form of hearing loss, sound is not transmitted into inner ear. If we do the math again, as only 8% of the population has a hearing loss at all, and 90% of them are sensorineural, this means that only 0.8% of the population has a conductive hearing loss. An example of conductive hearing loss is plugging up of the ear by ear wax. Other things that cause conductive hearing losses are fluid in the middle ear, and disorders of the small bones (ossicles) in the middle ear.