Food Allergy

Food Allergy Overview

For someone with a food allergy, eating or swallowing even a tiny amount of a particular food can cause symptoms such as skin rash, nausea, vomiting, cramping, and diarrhea. Because the body is reacting to something that is otherwise harmless, this type of allergic reaction is often called a hypersensitivity reaction. Rarely, a severe allergic reaction can cause a life-threatening set of symptoms called anaphylaxis, or anaphylactic shock.

Although about 25% of people believe they have a food allergy, only about 2.5% of adults and about 6-8% of children, mainly younger than 6 years, have true food allergies. The rest have what is known as food intolerance—an undesirable reaction to a food that does not involve the immune system.

It is easy to confuse food intolerance with food allergy because they can have similar symptoms. With food intolerance, however, you usually get only mild symptoms such as an upset stomach.

• A common example of food intolerance is lactose intolerance—a condition in which a person is missing a certain enzyme necessary to digest dairy proteins. The result is loose stools, gas, and nausea after consuming dairy products such as milk or cheese.
  
  
• Another example of food intolerance is reaction to MSG. MSG, or monosodium glutamate, is a white-colored additive used to enhance the flavor of food. It is a fermented mixture of glutamic acid, sodium, and water and is used mainly in Asian cooking. Over the last 30 years, side effects from MSG have been related to its use in Chinese food and referred to as the Chinese restaurant syndrome. In this syndrome, MSG was suggested as the cause of the symptoms following a Chinese meal. In 1995, a new term was coined, the MSG symptom complex, to include all the reactions that were reported to be related to MSG. These reactions are not a true food allergy, and the exact cause of the reactions is unknown.

Food Allergy Causes

An allergic reaction occurs when the body's immune system overreacts to an allergen, in this case a food protein.

• The white blood cells produce an antibody to this allergen, called immunoglobulin E or IgE.
  • When this antibody comes in contact with the particular food protein, it promotes production and release of certain chemicals called "mediators." Histamine is an example of a mediator.
  • These mediators act on various parts of the body, mainly the skin, throat, airways, intestines, and heart.
  • The effects of the mediators on organs and other cells cause the symptoms of the allergic reaction.

• Any food has the potential to trigger an allergic reaction, but a few foods account for most food allergies. In fact, about 90% of food allergies are triggered by one of these 8 foods:
  • Eggs
  • Milk
  • Wheat
  • Soy
  • Peanuts
  • Tree nuts
  • Fish
  • Shellfish

• Generally, people who have allergies react to only a few foods. Occasionally a person who is allergic to one food also may be allergic to other related foods. This is called cross-reaction. Common examples:
  • Allergy to peanuts - Cross-allergies to soybeans, green beans, and peas
  • Allergy to wheat - Cross-allergy to rye
  • Allergy to cow's milk - Cross-allergy to goat's milk
  • Allergy to pollen - Cross-allergies to foods such as hazelnuts, green apples, peaches, and almonds

• People who have a history of other allergies, such as eczema or asthma, are particularly prone to having a reaction to a food. They are also more likely to have a more severe reaction.

Food Allergy Symptoms

A person with a food allergy can have symptoms beginning as soon as 2 minutes after eating the food, but reactions may take 1-2 hours to appear. Occasionally, symptoms abate quickly, only to recur in 3-4 hours.

• The most common symptoms include the following:
  • Itching of the skin followed by hives, a rash of raised, reddish bumps or wheals
  • Swelling of the lips and mouth
  • Belly cramps
  • Nausea
  • Vomiting
  • Diarrhea

• Other symptoms may include the following:
  • Itching and watering in the eyes
  • Runny or stuffy nose

• Symptoms of a more severe reaction could include the following:
  • Shortness of breath or difficulty breathing
  • Tightness in the chest
  • Feeling of tightness or choking in the throat
  • Rapid or irregular heart beat
  • Feeling dizzy or light-headed
  • Losing consciousness

• A severe allergic reaction can be life threatening. This severe reaction is referred to as anaphylaxis, or anaphylactic shock.
  • The dizziness, light-headedness, and loss of consciousness are due to dangerously low blood pressure, called "shock."
  • An anaphylactic reaction can begin suddenly, or it may develop gradually with itchiness and swelling of the skin and throat and then progress to a severe reaction over a few hours.
  • Most people get such a reaction immediately after eating the food, but in a few unusual cases the reaction occurs only after exercising following the ingestion of the food.
  • Severe reactions are most often seen with allergies to nuts, fish, and shellfish, although allergy to any food can cause anaphylaxis.
  • People with asthma, childhood allergies, eczema, or prior severe food allergies are especially at risk for having an anaphylactic reaction.

• MSG reaction can be mistaken for an allergic reaction.
  • Symptoms of MSG reaction include the following:
    • Burning sensation at the back of the neck and radiating down the arms and chest
    • Tingling and numbness in the same areas
    • Headache
    • Nausea
    • Occasionally, difficulty breathing, especially in those with poorly controlled asthma
      
      
  • A few people experience seizures, irregular heartbeats, and anaphylaxis after the use of MSG.
  • Contrary to popular beliefs, MSG has no relation to Alzheimer disease, Huntington chorea, or other chronic illnesses.

When to Seek Medical Care

If you experience symptoms of food allergy, call your health care provider right away for advice.

• He or she may recommend that you go to a hospital emergency department.
• If you are unable to reach your health care provider and are concerned about your symptoms, go to the emergency department.
• Severe reactions, including symptoms such as difficulty breathing, dizziness or light-headedness, or tightness or choking in the throat, require treatment in an emergency department.
• Even mild symptoms that are not improving or are getting worse require evaluation in an emergency department.

Do not attempt to drive yourself to the hospital. If no one is available to drive you immediately, call 911 for emergency medical transport. While waiting for the ambulance to arrive, start self-treatment.

Exams and Tests

Generally a food allergy is identified by signs and symptoms. Medical professionals are trained to recognize hives, swelling patterns, rashes, and other symptoms associated with allergic reactions.

You will be asked questions about your medical history and possible triggers of the reaction.

Blood tests and other tests are needed only under very unusual circumstances, such as anaphylaxis.

Some people can pinpoint which food caused the allergic reaction, especially if the reaction occurs within minutes of consuming a particular food. Many others will need to see an allergist for special testing to determine the exact food that is responsible.

Food Allergy Treatment

After getting advice from your health care provider, some mild allergic reactions may be treated at home. Any worsening of symptoms requires medical attention.

Self-Care at Home

For localized hives or other mild skin reactions

• Take cool showers or apply cool compresses.
• Wear light clothing that doesn't irritate your skin.
• Take it easy. Keep your activity level low.
• To relieve the itching, apply calamine lotion or take over-the-counter antihistamines, such as diphenhydramine (Benadryl) or chlorpheniramine maleate (Chlor-Trimeton).

For all other reactions, especially severe reactions, self-treatment is not recommended. Have a companion drive you to the hospital emergency department, or call 911. Here's what you can do while waiting for the ambulance:

• Try to stay calm.
• If you can identify the cause of the reaction, prevent further exposure.
• Take an antihistamine (1-2 tablets or capsules of diphenhydramine [Benadryl]) if you can swallow without difficulty.
• If you are wheezing or having difficulty breathing, use an inhaled bronchodilator such as albuterol (Proventil) or epinephrine (Primatene Mist) if one is available. These inhaled medications dilate the airway.
• If you are feeling light-headed or faint, lie down and raise your legs higher than your head to help blood flow to your brain.
• If you have been given an epinephrine kit, inject yourself as you have been instructed. The kit provides a premeasured dose of epinephrine, a prescription drug that rapidly reverses the most serious symptoms (see Follow-up).
• Bystanders should administer CPR to a person who becomes unconscious and stops breathing or does not have a pulse.
• If at all possible, you or your companion should be prepared to tell medical personnel what medications you have taken that day, what you usually take, and your allergy history.

Medical Treatment

In a severe reaction, the first priority is to protect your airway (breathing) and your blood pressure.

Your health care provider will make sure that your airway is open and that you are getting enough oxygen.

• Oxygen may be given through a tube into the nose or by face mask.
• In severe respiratory distress, mechanical ventilation may be required. A tube is placed in the mouth to keep the airway open.
• In rare cases, a simple surgery is performed to open an airway.

Your blood pressure will be checked frequently.

• An IV line may be started.
• This is used to give saline solution to help boost blood pressure.
• It also may be used to give medication.

You may need to be admitted to the hospital for further monitoring and treatment.

Medications

The choice of medication and how it is given depends on the severity of the reaction.

• Epinephrine
  • This drug is given only in very severe reactions (anaphylaxis).
  • Epinephrine is injected and acts as a bronchodilator (dilates the breathing tubes).
  • It also constricts the blood vessels, increasing blood pressure.
  • Another medication with similar effects may be given instead.
  • For a less severe reaction involving the respiratory tract, an inhaled epinephrine bronchodilator may be used, as in asthma.
• Diphenhydramine (Benadryl)
  • This drug reverses the actions of histamine.
  • Diphenhydramine is injected when quick action is required.
  • It may be given by mouth for a less severe reaction.
• Corticosteroid
  • One of this group of drugs is usually given IV at first for rapid reversal of the effects of the mediators.
  • These drugs should not be confused with the steroids taken by athletes to build muscle and strength.
  • These drugs reduce swelling and many other symptoms of allergic reactions.
  • You may need to take an oral corticosteroid for several days after this.
  • Oral corticosteroids are often given for less severe reactions.
  • A corticosteroid cream or ointment may be used for skin reactions.
  • Other medications may be given as needed.

Follow-up

Be sure to let your primary health care provider know about the reaction later if he or she was not involved in your treatment.

An allergy specialist (allergist) can determine the difference between true food allergy and food intolerance.

• The allergist will ask you about the sequence of events that led to the reaction and record a thorough dietary and medical history.
• He or she may use special tests to find out which food is responsible for the allergic reaction.
• By conducting these tests, the allergist can identify the food responsible for the allergy and help create a plan for avoiding that particular food.

The first step in evaluation for food allergies is testing.

• Skin test: Dilute extracts of various foods are placed on the skin. The allergist looks for the formation of a bump on the skin after 10-20 minutes. Swelling at the site of the test can mean that you are allergic to that particular food.
• Blood test: This may be used to check for antibodies against specific food allergens. These results are confirmed with the oral challenge test in which small doses of the suspected food are given in a mixture of different foods to look for a reaction. If symptoms develop, then you are proven to have allergies to the particular food.
• Elimination diet: With this test, you stop eating foods that may be triggers. Gradually these foods are re-introduced back into the diet. The allergist will then be able to pinpoint the allergy-causing food if a reaction occurs.

Individuals with food allergies and their family members should have a clear plan of action in case of an accidental ingestion of the offending food. Emergency medications such as antihistamines and epinephrine should always be available.

• Susceptible people should keep with them an epinephrine kit (brand names are Epi-Pen, Ana Kit, Ana Guard) in case of exposure to the allergen.
• The kit contains a premeasured dose of epinephrine in an easy-to-use syringe for self-injection.
• You inject the medicine into your thigh as soon as you feel an allergic reaction coming on.
• Even if you inject yourself with epinephrine, you should still proceed immediately to a hospital emergency department.
• It is not unusual for a reaction to abate and then return within a few hours. Even if you require no further treatment, you should remain at the hospital until 4-6 hours after the beginning of the reaction.

Prevention

The only sure way to prevent future food allergies is to avoid eating a trigger food. Take care because a trigger can be present in many different foods; only a trace amount can cause a reaction.

• Learn to read food labels carefully and know which ingredients you should avoid.
• When eating in restaurants, ask what ingredients are in foods you would like to order.
• Avoid foods whose ingredients you can't confirm.
• Work with a registered dietitian to plan safe menus.
• Check into special food-allergy cookbooks and groups such as the Food Allergy & Anaphylaxis Network that deal with issues specific to food allergies.

Be prepared to deal with an anaphylactic reaction if you are exposed to the culprit food again. If you have had a severe reaction before, carry your epinephrine kit.

Never underestimate the danger of an allergic reaction.

Allergy shots are given to some people who have persistent and disruptive food allergy symptoms.

• The shots do not treat symptoms, but by altering the immune response they prevent future reactions. (This is referred to as immunotherapy.)
• Treatment involves a series of shots, each containing a slightly greater amount of the antigen(s) that cause the reaction.
• Ideally, the person will become "desensitized" to the antigen(s) over time.
• These are still under investigation and have not been proven to prevent allergic reactions.
• The effectiveness of shots varies by individual.

Outlook

Most people with food allergies do well if they are able to avoid their trigger foods. With time, many people lose their antibodies to the foods to which they once were allergic to, or "outgrow" the allergy.

• This is most likely to happen if the trigger food is identified and eliminated from the diet.
• This is especially true in children who, by about the age of 10 years, may outgrow their allergies—mainly to milk and eggs.
• Allergies to nuts, fish, and shellfish can last a lifetime.

One you have had a reaction to a food, you are more likely to have a severe reaction if exposed to the trigger.

Support Groups and Counseling

Allergy and Asthma Network--Mothers of Asthmatics

Asthma and Allergy Foundation of America
1233 20th St. NW, Suite 402
Washington, DC 20036
(202) 466-7643

Food Allergy and Anaphylaxis Network (FAAN)

For More Information

Web Links

American Academy of Allergy, Asthma and Immunology

American College of Allergy, Asthma and Immunology

Food Allergy and Anaphylaxis Network (FAAN)

Synonyms and Keywords

allergen, allergic reaction, anaphylactic shock, anaphylaxis, antibodies, antibody, Chinese restaurant syndrome, food hypersensitivity, food intolerance, trigger food, cross-reaction, immunoglobulin E, IgE, monosodium glutamate, MSG, hives, antihistamine, epinephrine kit, allergy to food, food allergies, food allergy

Authors and Editors

Author: Jatinder Singh, MD, Staff Physician, Department of Emergency Medicine, St Luke's Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons.

Coauthor(s): Mark Clark, MD, Associate Program Director, Clinical Assistant Professor, Department of Emergency Medicine, St Luke's/Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons.

Editors: Scott H Plantz, MD, FAAEM, Research Director, Assistant Professor, Department of Emergency Medicine, Mount Sinai School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; James S Cohen, MD, Consulting Staff, James Cohen, PC.

Taken From : http://www.emedicinehealth.com