Causes of food allergy

What causes food allergy?

Food allergies occur when the immune system mounts an attack on certain proteins in certain foods. The substances in the food that cause this immune system response are called allergens. The immune system is a complex network of cells and molecules that help defend the body against unknown substances. When a properly functioning immune system detects an unknown substance, it responds to this threat by producing proteins called antibodies against the invaders. The antibodies will recognize and attack this foreign substance when they next encounter it.

This "battle" is what causes the allergy symptoms. In food allergy the immune system mistakenly sees a harmless substance in the food as harmful, and churns out antibodies known as immunoglobulin to attack it. These antibodies will circulate in the blood, attached to special cells called mast cells, which are part of the immune system. This occurs in order to protect against future invasion by that substance. The next time a person eats that food, the substance to which he is allergic the allergen enters the body, and attaches to the immunoglobulin on mast cells.

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The mast cells respond by releasing a host of powerful chemicals, including histamine, to protect the body. This produces allergic symptoms. Histamine contributes to inflammation and causes symptoms such as swelling on the skin and itching. It is responsible for the hives, or welts, that appear on the skin when a doctor tests for allergy. These hives show the presence of immunoglobulin and are one of the best indications of allergy.

What are the symptoms of food allergy?

In an allergy attack, the symptoms experienced depend on where in the body histamine is released.

Allergic reactions to foods most often involve the skin, the stomach and intestines, and the mouth and the respiratory system. A life threatening reaction may involve all parts of the body including the cardiovascular system so that the individual goes into shock this will lead to blood pressure to fall dangerously low. A severe reaction could start very suddenly and involve only a fall in blood pressure or shock. It is important to know that a life threatening reaction may occur with no skin symptoms. Symptoms may appear within minutes or as long as several hours after eating the allergy provoking food.

An allergy reaction in the skin may cause hives, itchy, scaly rash called eczema, redness or flushing, and swelling. In the digestive system an allergy reaction may cause stomach pain, nausea, vomiting, and diarrhea. An the common respiratory symptoms from an allergic reaction may include sneezing, coughing, runny nose, wheezing, closing of the throat and breathing difficulties, as part of a severe allergic reaction known as anaphylaxis and, itchy, watery eyes are often included with respiratory symptoms.

Life-threatening reactions (anaphylaxis)

The most severe allergic reaction is anaphylaxis, or anaphylactic shock, a severe reaction that involves most of the body. Anaphylaxis can affect several parts of the body at the same time, including the skin and the digestive and respiratory systems or it might just involve respiratory or cardiovascular symptoms. In addition to producing the symptoms of food allergy, it may also lead to difficulty in breathing, falling blood pressure and unconsciousness. Although very rare, anaphylaxis can be fatal. Each year, about 150 people in the United States die of food-related anaphylaxis.

Which foods cause allergic reactions?

Virtually any food can trigger an allergic response. However, studies have found that 80 to 90 percent of children with food allergies are allergic to one or more of these foods for example eggs, peanuts, milk, wheat, and soy. Other common triggers include tree nuts such as almonds, pecans, cashews, Brazil nuts and walnuts, and fish and shellfish for example, crab and shrimp. Various other foods and certain food additives and spices may cause allergic reactions.

Cross reactions

Sometimes, an individual's allergic reaction to a particular food extends to other foods that contain similar allergens, a phenomenon called cross reactivity. For example, someone who is allergic to peanuts may also have a problem with other legumes, such as soybeans or peas. However, it may be surprising to know that the vast majority of food allergic individuals rarely react to other legumes. In fact, more peanut allergic children seem to be allergic to eggs or tree nuts than to other legumes. Cross reactions can develop between foods with allergens similar to those of other allergy provoking substances, such as plant pollens.

Researchers have found, for example, that some people who suffer hay fever symptoms when they inhale birch pollen also have an allergic reaction when they eat kiwi fruit or apples.

How do you find out if you have food allergies?

If you think you have food allergies, you should see an allergist, a physician who specializes in diagnosing and treating allergies. If you try to diagnose the problem yourself, you run the risk of removing too many foods from your diet and losing important nutrients. Before making a diagnosis, an allergist will take your medical history and ask whether you have a family history of allergies.

The doctor will ask detailed questions aimed at uncovering a possible relationship between the symptoms and your diet, such as, what kinds of symptoms does the suspected food or foods produce? How much time elapses between eating the food and the onset of symptoms? How much of the food do you have to eat to trigger a reaction? How many times has eating the food caused a reaction? When was the last time you had a reaction to the food? These are several questions that the doctor will ask.

Controversial tests and treatments

There are some questionable practices for diagnosis and treatment of food allergies. Tests that are not scientifically valid and are considered experimental including, Blood tests that determine food immune complexes and IgG food antibodies. This tests measure substances that all normal people have in their blood. Food immune complexes form after food digestion. IgG includes most of the protective antibodies, including those that form when you receive a vaccine or after an infection. It is unclear whether people with allergies make abnormal amounts of these substances.

Cytotoxic test, this test involves adding a food allergen to someone's blood sample and examining the reaction of white blood cells under a microscope. If the cells change shape, decrease or die, the person is thought to be allergic to that food. No proof exists that this test is effective for diagnosing food allergy. Provocation and neutralization, in the subcutaneous under the skin form of this test, a food extract is injected under the skin. In the sublingual under the tongue form, the food extract is placed under the person's tongue.

If the person has an allergic reaction, he or she receives more of the substance. The belief is that the second dose neutralizes, or relieves, the symptoms. In reality, it can cause a severe allergic reaction. Some doctors use provocation and neutralization to try to desensitize allergic people to foods. But the technique has been found to be ineffective for both diagnosis and treatment of allergies.

How to cope with food allergy?

Most people with food allergies will be put on an elimination diet one from which foods suspected of causing an allergic reaction are removed.

It may be difficult to stop eating some foods, such as those made with wheat or milk. Fortunately, there are many foods on the market that substitute for the more common allergy provoking foods.

Creating a food plan

For help in restricting your diet after a food allergy diagnosis, consult your doctor or a registered dietitian. Dietitians can help design a food plan, suggest alternative foods or ingredients to replace forbidden ones, and provide instruction on reading food labels. You may find it helpful to use an allergy free cookbook, which gives recipes that omit common food allergens.

Prepared allergen free items, such as rice bread and soy beverages, are available at health food stores and some grocery stores. It is not always possible to avoid the offending food. Your physician may give you medication to treat symptoms resulting from food allergies. Avoiding Accidental Ingestion Despite precautions, people with histories of food reactions sometimes unknowingly consume a food to which they are allergic. This can happen when the person is unaware of an ingredient in a dish someone else has prepared.

Or perhaps the offending ingredient is not on the label or is expressed in a term that does not clearly describe the ingredient. People with severe food allergies need to be aware that tiny amounts of allergens left on pots, pans, and cooking utensils can contaminate other foods. To avoid this kind of danger, people with severe food allergies are advised to make certain that pots, pans, and cooking utensils are carefully washed with soap and water after each use to remove any traces of forbidden foods.

How is food allergy treated?

Once an allergy is diagnosed, strict avoidance of the offending food or foods is the only proven method of managing the allergy. There is no medical cure for food allergy. However, within the next few years there will be safe and effective vaccines for food allergies. By strictly avoiding the food for one or two years, approximately one third of children and adults can lose their sensitivity to that food. But few children or adults outgrow their allergies to peanuts, tree nuts, and shellfish.

Although there are no medications currently available to treat food allergies, there are drugs on the market to treat symptoms of food allergies. The proper treatment depends on the severity of the allergic reaction. Antihistamines can help control mild reactions. These drugs have side effects, however. Over the counter Antihistamines cause drowsiness. Your doctor can prescribe an antihistamine that will not make you sleepy. Asthma medication can be useful for people who wheeze during an allergic reaction.

In rare instances, food allergies may bring on an asthma attack. These attacks may be very severe. Epinephrine is used to treat anaphylaxis, a life threatening complication of food allergy. Doctors advise people with severe food allergies always to carry a self injecting device loaded with epinephrine or a kit containing a needle and syringe and to inject themselves at the first sign or symptoms.

References

1. (2005). Common food allergies. Cortlandt Forum, 18(11), 38-45. Retrieved from Academic Search Complete database.

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