Ear mites are insects that live and thrive in the ear canal.  Ear mites cause excess wax production, severe itching and inflammation, and the production of a dark brown grainy discharge.  They can lead to ear infections, which may cause foul odors, and are extremely contagious from pet to pet.  Ear mites can be detected by a microscopic exam of ear discharge and are treated topically.  Yeast and different bacteria can also cause ear diseases.  These organisms cause thick discharges and odors, itching, pain, and ear damage.