ABSTRACT
As we saw in Cases 32 and 33, allergic or hypersensitivity reactions to otherwise innocuous antigens occur in certain individuals. The site of such reactions and the symptoms they produce vary depending on the type of allergen and the route by which it enters the body. When inhaled or ingested allergens enter the bloodstream they can be carried to the skin, where they induce a chronic inflammation-known as atopic dermatitis-in sensitized (atopic) individuals who possess T cells and IgE specific for an allergen. Allergens that act by direct skin contact can also incite inflammation. The immunologic response of the skin to antigen is complex, resulting in inflammation and localized tissue destruction. This chronic inflammation is called eczema and is the most prominent symptom of atopic dermatitis.
