Flea allergy dermatitis, FAD, is an eczematous itchy skin disease of dogs and cats. For both of these domestic species, flea allergy dermatitis is the most common cause of skin disease. Affected animals develop allergic reactions to chemicals in flea saliva. Symptoms of this reaction include erythema (redness), papules (bumps), pustules (pus-filled bumps), and crusts (scabs). If severe, hair loss will occur in the affected area. Dogs with flea allergy dermatitis often show hair loss and eczematous skin rash on the lower back, upper tail, neck, and down the back of the legs. Cats with flea allergy dermatitis may develop a variety of skin problems, including feline eosinophilic granuloma, miliary dermatitis, or self-inflicted alopecia from excessive grooming.