Dog ears and cat ears
Dogs have ears which have evolved to be self-cleaning. The skin grows outwards and carries debris towards the opening of the ear, like a conveyor belt.
The external ear canal is L-shaped with a vertical canal, then a horizontal canal, leading up to the ear drum (the membrane separating the delicate hearing and balance organs from the outside environment).
While the common yeast or fungal growth on a dog's skin is quite normal and causes no problems, it can proliferate and cause disease when there is a change is the dog's underlying health.
Ear problems in dogs are not uncommon. Many normal dog ears will have some bacteria present, but a change in the underlying health of the ear can make this normal flora proliferate, cause disease and can allow other environmental bacteria to invade.