Atopic dermatitis: A skin disease characterized by areas of severe itching, redness, scaling, and loss of the surface of the skin. Atopic dermatitis is the most common of the many types of eczema. Atopic dermatitis is frequently associated with other allergic disorders, especially asthma and hay fever. A defect of the immune system within the skin has been detected in patients who have atopic dermatitis, but the reason for the defect is unknown.
