It is caused by a scabies mite. This skin problem is transmissible to humans, causing a bad rash. A topical spray or ointment can eliminate the pest in both people and dogs. Dogs are allergic to many of the same things that people are, including dust and pollen. Veterinarians can often determine the source of the allergies and desensitize the animal through allergy shots.
Cats can pass ringworm, a fungus, on to humans.
Look for a crusty, circular lesion on the animal's face. A topical antifungal cream usually wipes out this pesky invader, but sometimes treatment is prolonged.