Overall, allergic diseases are among the major causes of
illness and disability in the United States, affecting as many as 40 to
50 million Americans.
An allergy is a specific immunologic reaction to a normally harmless
substance, one that does not bother most people. People who have
allergies often are sensitive to more than one substance. Types of
allergens that cause allergic reactions include pollens, dust
particles, mold spores, food, latex rubber, insect venom, or medicines.
Scientists think that people inherit a tendency to be allergic,
meaning an increased likelihood of being allergic to one or more
allergens, although they probably do not have an inherited tendency to
be allergic to any specific allergens. Children are much more likely to
develop allergies if their parents have allergies, even if only one
parent is allergic. Exposure to allergens at certain times when the
body's defenses are lowered or weakened, such as after a viral
infection or during pregnancy, seems to contribute to the development
of allergies.
Normally, the immune system functions as the body's defense against
invading agents such as bacteria and viruses. In most allergic
reactions, however, the immune system is responding to a false alarm.
When an allergic person first comes into contact with an allergen, the
immune system treats the allergen as an invader and mobilizes to
attack. The immune system does this by generating large amounts of a
type of antibody (a disease-fighting protein) called immunoglobin E, or
IgE. Each IgE antibody is specific for one particular allergenic
(allergy-producing) substance.
The signs and symptoms are familiar to many:
- Sneezing often accompanied by a runny or clogged nose.
- Coughing and postnasal drip.
- Itching eyes, nose, and throat.
- Allergic shiners (dark circles under the eyes caused by increased blood flow near the sinuses).
- The "allergic salute" (in a child, persistent upward rubbing of the nose that causes a crease mark on the nose).
- Watering eyes.
- Conjunctivitis (an inflammation of the membrane that lines the
eyelids, causing red-rimmed, swollen eyes, and crusting of the eyelids).
In people who are not allergic, the mucus in the nasal passages
simply moves foreign particles to the throat, where they are swallowed
or coughed out. But something different happens to a person who is
sensitive to airborne allergens.
As soon as the allergen lands on the mucous membranes lining the
inside of the nose, a chain reaction occurs that leads the mast cells
in these tissues to release histamine and other chemicals. These
powerful chemicals contract certain cells that line some small blood
vessels in the nose. This allows fluids to escape, which causes the
nasal passages to swell, resulting in nasal congestion.
Histamine also can cause sneezing, itching, irritation, and excess
mucus production, which can result in allergic rhinitis (runny nose).
Other chemicals made and released by mast cells, including cytokines
and leukotrienes, also contribute to allergic symptoms.
Avoiding exposure to allergens prevents allergic rhinitis. This
means avoiding animals if you are allergic to them, and staying in
doors and using the air conditioner during times of high pollen counts.
In adults, the most common foods to cause allergic reactions include:
- shellfish such as shrimp, crayfish, lobster, and crab;
- peanuts, are one of the chief foods to cause severe anaphylaxis, a
sudden drop in blood pressure that can be fatal if not treated quickly; - tree nuts such as walnuts;
- fish;
- and eggs.
In children, the pattern is somewhat different. The most common food
allergens that cause problems in children are eggs, milk, and peanuts.
Adults usually do not lose their allergies, but children can sometimes
outgrow them. Children are more likely to outgrow allergies to milk or
soy than allergies to peanuts, fish, or shrimp.
The causes of nonimmunologic adverse reactions to foods include food
toxicities, food poisonings, and pharmacologic or metabolic reactions.
Such intolerances occur more frequently than true food allergies and
are related to dose as well as to the concurrent presence of
medications, other diseases, or genetic errors of metabolism.
Tartrazine is used in foods, beverages, drugs and cosmetics. It has
been estimated that about 100 000 persons in the United States are
sensitive to this substance. Symptoms of allergy include generalized
urticaria, swelling, often of the face and lips, runny nose, and on
occasion even life threatening asthma. Since tartrazine is found in a
large number of products, tartrazine-sensitive individuals are advised
to read labels and avoid food containing tartrazine.
The allergic-type reactions range from mild to severe, and in some
cases can cause death. "Sulfites" or "sulfating agents" are general
terms used to describe sulfur based substances that have been in
widespread use for many years by the food and drug industries. They
include sulfur dioxide, sodium sulfite, sodium and potassium bisulfite,
and sodium and potassium metabisulfite. Although they have various
permitted uses, their primary function is as a preservative or
antioxidant to prevent or reduce spoilage and discolouration during the
preparation, storage and distribution of many foods.
There is some evidence that some non-asthmatics also can suffer
adverse reactions to sulfites. For example, out of more than 500
reports of sulfite reactions investigated by the FDA, about one-fourth
involved people who had no known history of asthma.
Approximately 10 percent of people with asthma are sensitive to
ingestion of sulphite, which induces asthma. Foods containing sulfur
dioxide, as a preservative, should be used with caution.
Vitamin C may help alleviate some of the inflammation associated
with chronic allergies and a daily dose of about 400 milligrams of
magnesium should be taken to relieve respiratory problems.
See also: Hay fever (allergic rhinitis or pollinosis)
- Something in the Air: Airborne Allergens. National Institute of Allergy and Infectious Diseases, Published February 1998
