The external pinnae are usually haired. If the ear is pruritic, scratching may result in hair loss on the pinnae or at the base of the ear. There are some ear diseases that result in loss of hair from the pinnae in the absence of pruritis. For example, Daschund dogs may develop a non pruritic alopecia of the pinnae. The inner side of the pinnae are less haired than the external aspect.
Breeds vary in the amount of hair they have on the inner aspect of the pinnae.
Poodles often have very hairy ears while Boxer's ears have minimal hair on the inside of the pinnae. Animals with hairy ears will have reduced air flow in the ear canal are are predisposed to infection. The inside of the pinnae should be examined for redness, discharge and excoriation. If the ear is infected but discharge is not visible, the infection can often be detected by smelling the ear. I always smell the ear canal of awake dogs and cats as part of a routine physical examination.