| What is an allergic reaction?
 A hypersensitive response, or allergic "reaction," is the result
of how three factors interact with the body:
The allergen — Allergens include pollen, mold, dust mites, certain
foods, latex, animal dander, and others. Mast cells — Although mast cells are found throughout the body,
most reside in connective tissues such as those of the skin, tongue, the
lining of the nose and intestinal tract, the lungs, and upper
airways. Immunoglobulin E (IgE) — IgE is an allergic antibody, a type
of protein made by the immune system to recognize and fight specific body
"invaders." IgE coats the surface of the mast cells in tissues.
The first time an allergy-prone person is exposed to an allergen (such
as pollen), large amounts of the corresponding IgE antibodies (for example,
pollen IgE antibodies) are produced. The IgE antibodies cause the mast
cells to release inflammatory chemicals that cause swelling of tissues,
as well as histamine and several other chemicals that cause itching, engorgement
of blood vessels, increased secretions, and bronchospasm (tightening of
muscles that surround the airways). Some of these chemicals attract white
blood cells known as eosinophils. The eosinophils add more inflammatory
chemicals.
If the allergen is in the air, the allergic reaction will occur in the
eyes, nose and lungs. If the allergen is ingested, the allergic reaction
will occur in the mouth, stomach, and intestines. Sometimes enough inflammatory
chemicals are released to cause a reaction throughout the body, such as
hives, decreased blood pressure, shock, or loss of consciousness. This
severe type of reaction is called anaphylaxis and may be life-threatening.
What are the symptoms of allergies?
Allergy symptoms can be categorized as mild, moderate, or severe (anaphylactic).
Mild reactions include local symptoms (affecting a specific area
of the body) such as a rash or hives; itchy, watery eyes; and some congestion.
Mild reactions do not spread to other parts of the body. Moderate reactions include symptoms that spread to other parts
of the body. Symptoms may include itchiness that spreads or difficulty
breathing. A severe allergic reaction, known as anaphylaxis, is a rare,
life-threatening emergency in which the body’s response to the allergen
is sudden and affects the whole body (systemic). Anaphylaxis may begin
with severe itching of the eyes or face and within minutes progresses
to more serious symptoms, including swelling (which could result in difficulty
swallowing and breathing); abdominal pain; cramps; vomiting; diarrhea;
hives; and angioedema (hives in the throat). Mental confusion or dizziness
also may be symptoms, since anaphylaxis causes a quick drop in blood pressure.
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