<<Disclaimer: Verify this information before applying it to your situation.>>

        Allergic reaction is a hyperreaction of immune system to a certain
environmental antigen (called allergen), which may manifest on all the
surfaces with direct contact to the outside environment such as
gastrointestinal tract, lung and skin (or in the blood vessels after the
administration of an intravenous drug). By definition this reaction occurs
within minutes (hours) and it is the consequence of immunoglobulin E
production to this antigen. However, if somebody has had lot of specific
IgE immunglobulin to this antigen in the blood, the reaction may occur
within minutes after ingesting, inhaling or contacting the allergen. This
immunoglobulin binds to special cells (called mast-cells) in the skin or
lung or gastrointestinal tract causing the release of different compounds
stored in these specialized cells. The release of these compounds (e.g.
histamin)  causes different skin rashes (e.g angioedema), asthmatic
breathing or abdominal cramps with diarrhea.

        The intolerance term in the gastroenterology means that somebody
is not able to tolerate certain food components. It is a wide terminology.
First of all, it is not an IgE immunoglobulin-mediated process. There are
different mechanisms behind a gastrointestinal intolerances:

-The most common is the lactose intolerance, which is the consequence of a
decreased enzyme activity (lactase) in the small intestine. Because the
lactose is not digested and absorbed in the upper part of the small
intestine it goes down to the last part of the intestine and to the colon,
where the normal bacterial flora hydrolyzes the lactose. The unabsobed
lactose causes a so called osmotic diarrhea. The hydrolysis of lactose
sometimes results in only increased gaseoussness with crampy pain.


 -The gluten-intolerance is a other example. It is an immunoreaction to a
fragment of gliadin molecule in the small intestine, but it is not an IgE
immunglobulin mediated process. A more complex and different immunological
reaction occurs in the upper part of the small intestine, which does not
cause immediate symptoms, but slowly damages the segments of the small
intestine contacted with the gliadin molecule. As the damage goes down and
longer segments of small intestine has the damage (villus atrophy) the
symptoms may manifest.

-There is a transient intolerance to milk- and soy proteins in infants.
It may start within 1-4 weeks on milk or soy containing formulas. It may
cause diarrhea and bloody stools. The elimination of these proteins from
the diet results in a rapid improvement (within two weeks). From unknown
reason this intolerance is temporary only and most of the infants with
cow-milk or soy protein intolerance are able to tolerate these proteins
without any problem after two years of age. This suggests a temporary
immaturity or dysfuction in their gut immune system.

I hope this note helps to clarify the difference between allergy and
intolerance.

Karoly Horvath, M.D.
Baltimore