Histology finding of the normal and AD patient’s skin. (a) Histology of normal skin. Normal thickness of epidermis (top layer) composed of several layers of squamous cells with the delicate basket-wave keratin (stratum corneum) on the surface. The dermis (bottom part) is composed of sparse fibroblasts with abundant extracellular collagen bundles and embedded capillaries lined by a single layer of endothelial cells (magnification 200x). (b) Histology of subacute spongiotic dermatitis, typically seen in affected skin of AD patients. The epidermis is thickened with slit-like spaces between squamous cells, indicating edema/spongiosis. The overlying basket-wave keratin is replaced by abnormal hyperkeratosis and parakeratosis. The dermis shows increased cellularity composed of mixed inflammatory cells predominantly surrounding small vessels. The inflammatory cells are of predominantly lymphocytes with some mast cells, macrophages, and occasional eosinophils (magnification 200x).