Atopics may demonstrate an increased tendency toward this type of reaction which follows exposure to an antigen to which they have been previously sensitized. In its simplest form, this reaction presents as a hive or "wheal" (urticaria), but it may also be manifest as angioedema, anaphylaxis, hay fever, or asthma.

4. Elevated serum IgE

Patients with AD have a hereditary abnormality in the immune mechanism so that there is increased production of IgE antibodies. There appears to be a degree of positive correlation between the amount of IgE and the extent and severity of the AD.