Food allergy is an abnormal response to a food triggered by
the body’s immune system.
In adults, the foods that most often cause allergic
reactions include....
What Is Food Allergy?
Food allergy is an abnormal response to a food triggered by
the body’s immune system. In this section, food allergy
refers to a particular type of response of the immune system
in which the body produces what is called an allergic, or IgE,
antibody to a food. (IgE, or immunoglobulin E, is a type
of protein that works against a specific food.)
Allergic reactions to food can cause serious illness and, in
some cases, death. Therefore, if you have a food allergy, it is
extremely important for you to work with your healthcare
provider to find out what food(s) causes your allergic reaction.
Sometimes, a reaction to food is not an allergy at all but
another type of reaction called “food intolerance.”
Food intolerance is more common than food allergy. The
immune system does not cause the symptoms of food
intolerance, though these symptoms may look and feel
like those of a food allergy.
How Do Allergic Reactions Work?
An immediate allergic reaction involves two actions of your immune system:
• Your immune system produces IgE. This protein is
called a food-specific antibody, and it circulates through
your blood.
• The food-specific IgE then attaches to mast cells and
basophils. Basophils are found in blood. Mast cells
are found in body tissues, especially in areas of your
body that are typical sites of allergic reactions. Those
sites include your nose, throat, lungs, skin, and
gastrointestinal (GI) tract.
Generally, your immune system will form IgE against a food
if you come from a family in which allergies are common
—not necessarily food allergies but perhaps other allergic
diseases, such as hay fever or asthma. If you have two allergic
parents, you are more likely to develop food allergy than
someone with one allergic parent.
If your immune system is inclined to form IgE to certain
foods, you must be exposed to the food before you can have
an allergic reaction.
As this food is digested, it triggers certain cells in your
body to produce a food-specific IgE in large amounts.
The food-specific IgE is then released and attaches to the
surfaces of mast cells and basophils.
• The next time you eat that food, it interacts with
food-specific IgE on the surface of the mast cells and
basophils and triggers those cells to release chemicals
such as histamine.
• Depending on the tissue in which they are released,
these chemicals will cause you to have various symptoms
of food allergy.
Food allergens are proteins in the food that enter your
bloodstream after the food is digested. From there, they
go to target organs, such as your skin or nose, and cause
allergic reactions.
An allergic reaction to food can take place within a few
minutes to an hour. The process of eating and digesting
food affects the timing and the location of a reaction.
• If you are allergic to a particular food, you may first
feel itching in your mouth as you start to eat the food.
• After the food is digested in your stomach, you may
have GI symptoms such as vomiting, diarrhea, or pain.
• When the food allergens enter and travel through your
bloodstream, they may cause your blood pressure to drop.
• As the allergens reach your skin, they can cause hives
or eczema.
• When the allergens reach your mouth and lungs, they
may cause throat tightness and trouble breathing.
Cross-Reactive Food Allergies
If you have a life-threatening reaction to a certain food,
your healthcare provider will show you how to avoid similar
foods that might trigger this reaction. For example, if you
have a history of allergy to shrimp, allergy testing will usually
show that you are not only allergic to shrimp but also to
crab, lobster, and crayfish. This is called “cross-reactivity.”
Another interesting example of cross-reactivity occurs in
people who are highly sensitive to ragweed. During ragweed
pollen season, they sometimes find that when they try to
eat melons, particularly cantaloupe, they experience itching
in their mouths and simply cannot eat the melon. Similarly,
people who have severe birch pollen allergy also may react
to apple peels. This is called the “oral allergy syndrome.”
Common Food Allergies
In adults, the foods that most often cause allergic
reactions include
• Shellfish such as shrimp, crayfish, lobster, and crab
• Peanuts
• Tree nuts such as walnuts
• Fish
• Eggs
The most common foods
that cause problems in children are
• Eggs
• Milk
• Peanuts
• Tree nuts
Peanuts and tree nuts are the leading causes of the potentially
deadly food allergy reaction called anaphylaxis.
Adults usually keep their allergies for life, but children
sometimes outgrow them. Children are more likely to
outgrow allergies to milk, egg, or soy, however, than
allergies to peanuts. The foods to which adults or children
usually react are those foods they eat often. In Japan, for
example, rice allergy is frequent. In Scandinavia, codfish
allergy is common.
|
