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Food Allergy

Overview, Causes, & Risk Factors

A food allergy is an abnormal response of the immune system that is caused by the protein in certain foods. A food allergy is not the same as food intolerance. A person with food intolerance may have symptoms, such as abdominal distress, after eating a certain food. However, this response is not caused by the immune system.

What is going on in the body?

A food allergy occurs when an immune response occurs. An immune response is a normal response of the body to something it sees as abnormal. Usually the response is to bacteria, viruses, and toxins. Sometimes the body will recognize certain foods as abnormal. When foods are recognized as abnormal, the body produces an antibody known as IgE. IgE reacts with mast cells, which are part of the immune system. The reaction affects mast cells in many areas of the body, including the following:

  • lungs
  • nose and throat
  • skin
  • stomach and bowels
  • When the IgE reacts with the mast cells, histamine is produced. This chemical produces the symptoms of a food allergy.

    What are the causes and risks of the condition?

    A food allergy is an abnormal immune system response to protein in certain foods. Following are some of the foods that commonly cause food allergies:

  • eggs
  • fish
  • milk and other dairy products
  • peanuts and peanut oil
  • shellfish, such as shrimp and crab
  • soy
  • tree nuts, such as walnuts
  • wheat
  • whitefish
  • There is some evidence that genetically modified corn, known as StarLink, may cause severe allergic responses. This possibility is currently being investigated. Most people with food allergies also have other allergy-related disorders. These include nasal allergies to dust and pollen, eczema, and asthma.

    Symptoms & Signs

    What are the signs and symptoms of the condition?

    The symptoms of a food allergy develop as the protein in the food travels through the body. When the food is first eaten, the person may have itching in the mouth. After it's digested in the stomach, the individual may have vomiting, diarrhea, or abdominal distress.

    The food protein is absorbed into the bloodstream from the gut. The allergy may then cause a drop in blood pressure. When the proteins reach the skin, they can cause hives or rash. Once they reach the lungs, the person may have shortness of breath and wheezing.

    Reactions can vary in strength and can range from very mild to fatal. The symptoms usually occur within a few minutes to an hour after the person has eaten the food. Some people are so sensitive to particular foods that they can have an allergic response simply by inhaling or touching the food. Anaphylaxis is a severe systemic, or bodywide, allergic reaction. A person will feel as if his or her throat is closing. An anaphylactic reaction is a medical emergency. The emergency medical system should be contacted immediately.

    Diagnosis & Tests

    How is the condition diagnosed?

    Diagnosis of a food allergy begins with a medical history and physical exam. The healthcare provider may order other tests, including the following:

  • antibody titer tests to measure the level of IgE
  • double-blind food challenge, which tests the person's response to suspect foods
  • elimination diet, which removes the suspect food from the person's diet
  • skin tests

  • Prevention & Expectations

    What can be done to prevent the condition?

    In general, there is no way to keep from developing food allergies. There is some evidence that breastfeeding lowers an infant's chance of developing food allergies later.

    What are the long-term effects of the condition?

    Some children who develop food allergies outgrow them. However, food allergies are usually lifelong conditions. Effects range from abdominal discomfort to life-threatening anaphylaxis or death. Foods that cause allergic reactions should be avoided.

    What are the risks to others?

    Food allergies are not contagious and pose no risk to others.

    Treatment & Monitoring

    What are the treatments for the condition?

    Foods that cause an allergic response should be eliminated from the diet. It is important to read food labels carefully. Peanuts and milk, for example, are in many prepared foods.

    Following are some of the medications used to treat an allergic response:

  • antihistamines to block the mast cell reaction that causes symptoms
  • bronchodilators to open tight airways
  • corticosteroids to reduce the immune response
  • epinephrine to minimize the allergic response and prevent anaphylaxis
  • People with severe food allergies may carry either an EpiPen or an Ana-Kit. These are devices containing epinephrine to prevent anaphylaxis. These devices can be used by the person or a bystander to inject the medication.

    What are the side effects of the treatments?

    Bronchodilators and epinephrine raise the heart rate and blood pressure. Antihistamines can cause drowsiness and dry mouth. Corticosteroids may increase the risk for infection.

    What happens after treatment for the condition?

    Most individuals who have food allergies have them for their entire lives. Some children may outgrow food allergies. Food allergies can lead to dietary restrictions that may cause malnutrition if the restrictions are severe. Individuals with food allergies may have an overall change in normal lifestyle. The individual should wear a medical alert bracelet identifying the allergy.

    How is the condition monitored?

    Individuals should note if they are developing symptoms when they eat certain foods. They should also note whether different foods are causing allergic reactions. If these occur, a healthcare provider should be consulted. Any other new or worsening symptoms should also be reported to the provider.

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