**2.1 Definition**

Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease [1] that is characterized by non-IgE-mediated allergic skin inflammation, in which allergen-specific Th2 cells play a major role in the pathogenesis of the inflammation [2]. The appearance of atopic dermatitis is characterized by late eczematous reactions, which result from an allergen-specific Th2 immune response.
