Intrinsic Atopic Dermatitis and Extrinsic Atopic Dermatitis: Similarities and Differences

In atopic dermatitis (AD), recent research advances have portrayed a complex disease profile based on different subtypes/ phenotypes and underlying molecular mechanisms/endotypes. Extrinsic and intrinsic subdivision is one of the most common types, defined in terms of total serum immune globulin E (IgE) and/or specific IgE to food and environmental allergens. Extrinsic AD is the most common type (80%), with high IgE, impaired skin barrier, as well as high incidence of comorbid atopic diseases, whereas intrinsic AD accounted for 20% of AD, with normal IgE and intact barrier function. Clinical studies have shown that extrinsic AD was a classic Th2-based inflammatory dermatitis, while the intrinsic subtype presented increased Th1/Th17/Th22 but normal Th2 cytokines. Protein sensitization, a classic Th2 response, has been clearly characterized in extrinsic AD, while metal hapten induces intrinsic AD's sensitization, which may be associated with suprabasin deficiency. In this review, we aimed to further expand our knowledge about similarities and differences between these two subtypes, which will expand our capability to further dissect pathophysiology of AD and enable us to develop personalized medicine approaches.