Cause
There are several causes of otitis in cats.  One of the more common causes is ear mites called Otodectes cynotis, which are transmitted from one animal to another through close contact.  Dogs and cats can transmit ear mites to one another.  The mites that live in the ears cause significant irritation that leads to the production of a dark, brown, waxy material called cerumen.
 
Other causes of otitis include allergies to topical medications, to certain foods, and to particles or allergens in the air such as tree pollen and house dust.  Cats also can develop otitis when the normal yeast in the ear called Malassezia pachydermatis overgrows and causes a yeast infection.  Bacterial overgrowth in the ears also can cause infections.  Many more causes of otitis exist, so it is important that a veterinarian examine the cat thoroughly.