What are allergies?
Allergies are the immune system’s inappropriate and exaggerated response to a
foreign substance. Exposure to what is normally a harmless substance, such as
pollen, causes the immune system to react as if the substance is harmful.
Substances that cause allergies are called allergens.
When you come into contact with an allergen, you may experience
a number of symptoms including itchy, watery nose and eyes; asthma symptoms such
as wheezing and coughing; or hives.
What is an allergic reaction?
An "allergic reaction" is the result of how three factors interact in the
body:
1. The allergen — Allergens include pollen, mold, animal dander,
dust mites, medications, foods, latex, and others.
2. 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. Similar
cells, called "basophils" are present in the circulation.
3. 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 and basophils in
the bloodstream.
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 allergen is inspired
(breathed in), and an allergic reaction will occur in the eyes, nose, and/or
lungs. If the allergen is ingested, an 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, hives, and/or swelling, 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, progress to more
serious symptoms, including throat swelling (which could result in
difficulty swallowing and breathing); abdominal pain; cramps; vomiting;
diarrhea; hives (urticaria); and swelling (angioedema). Mental confusion or
dizziness may also result, since anaphylaxis may cause a drop in blood
pressure.