Developments allergy stem from a new appreciation of the immunology of classic immediate hypersensitivity (anaphylactic-type) reactions. Allergic reactions are now known to be biphasic, with an immediate component and a late component. When exposure to an allergen is long-term, inflammatory allergic reactions produce chronic symptoms. This understanding has provided a major change in the therapeutic approach to allergic diseases. Such insights are timely because an apparent worldwide epidemic of fatal asthma has occurred despite ever-increasing expenditures for asthma medications.
In allergic reactions, IgE attached to sensitized mast cells and basophils binds with the allergen and triggers the release of mediators. IgE-mediated cutaneous allergic reactions, like those that occur after beestings, have been known for years to be biphasic, ie, they have an immediate component (wheal and flare), which occurs within 20 minutes, and a subsequent late component (erythema and induration), which usually occurs 6 to 12 hours later. Biopsy specimens
Smith DL, deShazo RD. Allergy and Immunology. JAMA. 1994;271(21):1653-1654. doi:10.1001/jama.1994.03510450025013