An Overview of Food Allergy
Food allergy affects up to 6 to 8 percent of children under the age of three, and two percent of adults. Approximately 30,000 consumers require emergency room treatment and 150 Americans die each year because of allergic reactions to food.
If you have an unpleasant reaction to something you have eaten, you might wonder if you have a food allergy. One out of three people either believe they have a food allergy or modify their or their family's diet because of this belief. However, while food allergy is commonly suspected, healthcare providers diagnose a food allergy less frequently than most people believe.
A food allergy is an abnormal response, triggered by the body's immune system, to a 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) could be causing your allergic reaction.
Sometimes, a reaction to food is not a food 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 a food intolerance, though these symptoms can look and feel like those of a food allergy.
Food Allergy: How Do Allergic Reactions Work?
An immediate allergic reaction involves two actions of your immune system.
Your immune system produces immunoglobulin E (IgE), a type of protein that works against a specific food. This protein is called a food-specific antibody, and it circulates through the blood.
The food-specific IgE then attaches to mast cells, cells found in all body tissues. They are more often found in areas of your body that are typical sites of allergic reactions. Those sites include your:
- Nose
- Throat
- Lungs
- Skin
- 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. This is what happens in a typical allergic reaction:
- As the specific 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.
- The next time you eat that food, it interacts with food-specific IgE on the surface of the mast cells and triggers the cells to release chemicals such as histamine.
- Depending upon the tissue in which they are released, these chemicals will cause you to have various symptoms of food allergy.
Food allergens are proteins within 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 from within a few minutes up 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 lungs, they may cause asthma.
Food Allergy and Cross-Reactivity
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 food allergy to shrimp, testing will usually show that you are allergic not only 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 Causes of Food Allergy
Food allergy patterns in adults differ somewhat from those in children. The most common foods to cause
allergies in adults are:
- Shrimp, lobster, crab, and other shellfish
- Peanuts (one of the chief foods responsible for severe anaphylaxis)
- Walnuts and other tree nuts
- Fish
- Eggs.
In children, eggs, milk, peanuts, soy, and wheat are the main culprits.
Children typically outgrow their food allergy to milk, egg, soy, and wheat, while allergies to peanuts, tree nuts, fish, and shrimp usually are not outgrown. Adults usually do not lose their food allergies.
Food Allergy or Food Intolerance?
If you go to your healthcare provider and say, "I think I have a food allergy," your healthcare provider has to consider other possibilities that may cause symptoms and could be confused with food allergy, such as food intolerance. To find out the difference between food allergy and food intolerance, your healthcare provider will go through a list of possible causes for your symptoms. This is called a "differential diagnosis." This type of diagnosis helps confirm that you do indeed have a food allergy rather than a food intolerance or other illness.
(Click Food Intolerance for more information about the various types of food intolerance.)
After ruling out food intolerances and other health problems, your healthcare provider will take several steps to find out if you have a food allergy to specific foods.
These steps may include a:
-
Detailed history
-
Diet diary
-
Elimination diet
-
-
Blood test
-
Food challenge.
Food
allergy treatment involves avoiding the foods that trigger the reaction. Once you and your healthcare provider have identified the food(s) to which you are sensitive, you must remove them from your diet. To do this, you must carefully read the ingredient list on each and every food you might eat.
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