My cat has black patches and hair loss on its ears.

First determine whether the black patches are dirt or scabs from skin disease. Plain dirt usually has no rash, itch or dandruff, though sticky dirt can cause hair loss and can be removed with a fine comb or cleanser.

If the area itches, has dandruff or open wounds, the scab is from skin disease. Disinfect with iodine and apply a targeted skin medicine such as an antifungal spray once or twice daily, and keep a collar on to prevent scratching during treatment.