Atopic dermatitis (AD) is a common pruritic allergic skin disease in dogs and cats. It is generally accepted to be a Type I (IgE or IgG) hypersensitivity and is believed to affect ~10% of the canine population. Its incidence in cats has not been reported. In some dogs IgE antibodies against environmental allergens cannot be demonstrated. Atopic-like dermatitis (ALD) has recently been defined as a pruritic skin disease in dogs with characteristic features of AD but negative tests for IgE antibodies.

Etiology and Pathogenesis

Animals with AD are thought to be genetically predisposed to become sensitized to allergens in the environment. Allergens are proteins that, when inhaled or absorbed through the skin, respiratory tract, or GI tract, evoke allergen-specific IgE production. These allergen-specific IgE molecules affix themselves to tissue mast cells or basophils. When these primed cells come in contact with the specific allergen again, mast cell degranulation results in the release of proteolytic enzymes, histamine, bradykinins, and other vasoactive amines, leading to inflammation (erythema, edema, and pruritus). The skin is the primary target organ in dogs and cats, but rhinitis and asthma can also occur in ~15% of affected animals.

Last full review/revision July 2011 by Patricia D. White, DVM, MS, DACVD