Study of atopic hypersensitivity revealed a common immune mechanism which further confirmed the allegiance of many allergists to atopy, with the exclusion of other allergic diseases from their field of interest. An inherited tendency to make excessive amounts of IgE antibody is one characteristic of atopic individuals. IgE reactions tend to be immediate, causing obvious allergic reactions.
Hay fever is the most clear-cut case of allergy.
Food antigens can trigger the mast cell mechanism at any point in their journey through the body. Lip, tongue, throat burning and swelling are most obvious. Acute abdominal pain, vomiting, and diarrhea follow. Antigen may not react in GIT but activate Type 1 responses in blood or target organs, especially lungs and connective tissue. By a practical evolution of allergy practice, those clinical problems which were diagnosable by skin reactions became the special property of allergists.