The three types of underlying allergies are parasite (fleas, mites), food allergy
, and pollen/dust allergies. If your dog
is already on a good flea control such as Advantage or Revolution, then parasites are less likely. Options to treat allergies are to continue to treat symptoms with medications such as antihistamines, fatty acids, bathing, antibiotics, occasional steroids, etc, or to identify and treat the underlying cause.