Allergic diseases are common hyper-immune disorders. Atopic dermatitis (AD) has a higher prevalence in industrialized countries. It has been suggested that association between genetic factors, environmental factors and gut microbiota would be major triggering factors for the development of atopic dermatitis. Hygiene hypothesis by a lack of early childhood exposure to diverse microorganism increases susceptibility to atopic dermatitis and other allergic diseases. Recent studies have demonstrated the complex interrelationship between skin barrier, genetic, environmental, pharmacologic, psychological and immunologic factors that contribute to the development and severity of AD. The current review will examine the immunological mechanism that contributes to AD as well as immunologic triggers involved in the pathogenesis.