Food Allergy
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
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Food Allergy Myths
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Jay W. Marks, MD
 Food
allergies are often misunderstood, even though
societal recognition of, and education about, the condition is increasing. See if you have heard – or
believed – any of the following myths about food allergies:
- "You're "allergic" to any food that gives you problems." This statement is
false, since there are several problems that can arise after eating specific
foods, the majority of which are unrelated to allergy. True allergies to foods
are immunologic reactions involving the class of immunoglobulins (proteins that
assist in the body's immune response) known as immunoglobulin (Ig)
E. Other kinds of reactions to foods that are not food allergies include food
intolerances (such as lactose
or milk intolerance
), food poisoning, and toxic reactions. The prevalence of food allergy in the population is much lower than
the prevalence of adverse reactions to foods. It is estimated that true food
allergies occur in 2-5% of the population.
- "All food allergies in children resolve as they get older." As they grow older, some children may
tolerate foods that previously caused allergic reactions. This is more likely
to happen in the case of allergies to milk, eggs, and wheat, in which the
severity of reactions (or symptoms) may decrease by late childhood. It is not
clear in all cases, however, if the improved symptoms are an indication that
the allergy has disappeared. For example, in wheat allergy (celiac disease) symptoms may improve, but a mild allergic reaction continues in
the intestine, and
symptoms and signs of the allergy may recur in later years.
On the other hand, milk allergy appears to truly disappear as children grow
older.
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Introduction to food allergies
Either food allergy or food intolerance affects nearly everyone at some point. When people have an unpleasant reaction to something they ate, they often think that they have an allergy to the food. Actually, however, only about 1% of adults and 3% of children have clinically proven true allergic reactions to food.
This difference between the prevalence of clinically proven food allergy and the public's perception of the problem is due primarily to misinterpreting food intolerance or other adverse reactions to food as food allergy. Food allergy is an abnormal response to food that is triggered by a specific reaction in the immune system and expressed by certain, often characteristic, symptoms. Other kinds of reactions to foods that are not food allergies include food intolerances (such as lactose or milk intolerance), food poisoning, and toxic reactions. Food intolerance also is an abnormal response to food, and its symptoms can resemble those of food allergy. Food intolerance, however, is far more prevalent, occurs in a variety of diseases, and is triggered by several different mechanisms that are distinct from the immunological reaction responsible for food allergy.
People who have food allergies must identify and prevent them because, although usually mild and not severe, these reactions can cause devastating illness and, in rare instances, can be fatal.
How do allergic reactions to food occur?
The allergens in food are those components that are responsible
for inciting an allergic reaction. They are proteins that usually resist the
heat of cooking, the acid in the stomach, and the intestinal
digestive enzymes. As a result, the allergens survive to cross the
gastrointestinal lining, enter the bloodstream, and go to target
organs, causing allergic reactions throughout the body. The mechanism
of food allergy involves the immune system and heredity.
Immune system: An allergic reaction to food involves two
components of the immune system. One component is a type of protein,
an antibody called immunoglobulin E (IgE), which circulates through
the blood. The other is the mast cell, a specialized cell that is found in
all tissues of the body. The mast cell is especially common, however,
in areas of the body that are typical sites of allergic reactions,
including the nose and throat, lungs, skin, and gastrointestinal
tract.
Heredity: The tendency of an individual to produce IgE against
something seemingly as innocuous as food appears to be inherited.
Generally, people with allergies come from families in which allergies are
common -- not necessarily to food but perhaps allergies to pollen, fur,
feathers, or drugs. Thus, a person with two allergic parents is more
likely to develop food allergies than someone with one allergic
parent.
Mechanism: Food allergy is a hypersensitivity reaction, meaning
that before an allergic reaction to an allergen in food can occur, a
person needs to have been exposed previously, that is, sensitized, to
the food. At the initial exposure, the allergen stimulates
lymphocytes (specialized white blood cells) to produce the IgE
antibody that is specific for the allergen. This IgE then is released
and attaches to the surface of the mast cells in different tissues of
the body. The next time the person eats that food, its allergen hones
in on the specific IgE antibody on the surface of the mast cells and
prompts the cells to release chemicals such as histamine. Depending
upon the tissue in which they are released, these chemicals cause the
various symptoms of food allergy.
Next: What are the symptoms and signs of food allergy? »
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