Fig. 1. One-way vertical flow pathogenesis model of atopic dermatitis.

This vertical model suggests that (1) environmental toxicants (e.g., volatile inorganic chemicals, air pollution, and food additives) induce immune dysfunction and hypersensitivity in genetically susceptible human subjects by decreasing the threshold for developing hypersensitivity reaction to environmental allergens and irritants; and (2) exposure to the allergens and/or irritants induces hypersensitivity reaction, chronic skin inflammation, skin barrier defect, and clinical manifestations of atopic dermatitis (pruritus and eczema). In this model, multiple modalities could be introduced to block multiple elements in the pathogenetic pathway for the treatment of atopic dermatitis. In addition, blocking the upper stream of the pathogenetic pathway of this model might be a more effective and fundamental therapeutic approach than blocking the lower stream of the pathogenetic pathway.