Do I have a food allergy?
If you encounter an unpleasant reaction after eating certain foods — hives, itching, swelling or trouble breathing — you may have a food allergy. Then again, you might not.

Many people believe they are allergic to specific foods. However true food allergies aren't as common as you might think. Only about 1 percent of the adult population actually has a true food allergy. This is little consolation if you've had a bad experience and fear a recurrence. That's why it's important to distinguish a food allergy from more common problems such as food intolerance, indigestion or other conditions.

If your reaction to a certain food becomes more than an inconvenience or the symptoms are severe, talk with your doctor. Tests or elimination diets can help diagnose food allergies, and you can take precautions to help prevent serious and even life-threatening responses to consuming culprit foods.

What causes a food allergy?
A true food allergy involves your body's immune system response to a specific food or component of a food. Your immune system produces immunoglobulin E (IgE) antibodies to fight against even a tiny amount of the culprit food or food component (the allergen). This in turn releases histamine and other chemicals that cause the alarming signs and symptoms that may be a threat to life. Histamine is partly responsible for most allergic responses, including dripping nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing and even anaphylactic shock.

About 90 percent of food allergies are triggered by certain proteins in:

  • Cow's milk
  • Egg whites
  • Peanuts
  • Wheat
  • Soybeans

Other common causes are:

  • Fish
  • Shellfish
  • Tree nuts
  • Beans
  • Corn

Chocolate, long thought by parents to be a culprit among children, seldom is a cause of allergy.

What are the symptoms?
For most people, reactions to certain foods are uncomfortable, but for others they are frightening, and possibly life-threatening. Symptoms of a food allergy usually develop within an hour of eating the offending food.

The most common symptoms of a true food allergy include:

  • Hives , itching or  eczema
  • Swelling of the lips, face, tongue and throat, or other parts of the body
  • Wheezing, nasal congestion or trouble breathing
  • Abdominal pain, diarrhea , nausea or vomiting
  • Dizziness, lightheadedness or fainting

In a severe allergic reaction to food, you may have more extreme versions of the above symptoms, or you may experience the following life-threatening symptoms:

  • Constriction of airways, including a swollen throat, resulting in trouble breathing
  • Shock, with a severe drop in blood pressure
  • Rapid pulse
  • Dizziness, lightheadedness or loss of consciousness

These symptoms constitute a life-threatening condition known as anaphylactic shock. Anaphylactic shock is a systemic (affects the whole body) reaction that is life threatening. Being assessed by your doctor for anaphylaxis is very important if you suspect you may have food allergies. Anaphylaxis patients are prescribed a special kit that includes an injection of epinephrine that, when administered immediately after the first symptoms, will halt the reaction. These kits are typically carried by severe allergy sufferers at all times.

Could it be something else?
Other reactions to food don't involve your immune system and, consequently, the release of histamine. These reactions aren't true food allergies. Instead, they may be food intolerances. Because food intolerances may involve many of the same symptoms as food allergies do — such as nausea, vomiting, cramping and diarrhea — they're often confused.

If you have a food intolerance, you usually can eat small amounts of problem foods without a reaction. By contrast, if you have a true food allergy, even a tiny amount of food may trigger an allergic reaction.

Common causes of food intolerance include:

  • Absence of an enzyme needed to fully digest a food.

    You may not have adequate amounts of some enzymes needed to digest certain foods. Insufficient quantities of the enzyme lactase, for example, make it difficult to digest lactose, the main sugar in milk products. Lactose intolerance can cause bloating, cramping, diarrhea and excess gas.

  • Irritable bowel syndrome .
  • Food contaminated by a toxin.

    Sometimes food poisoning can mimic an allergic reaction. Some types of mushrooms and rhubarb, for example, can be toxic. Bacteria in spoiled tuna and other fish can also make a toxin that triggers adverse reactions.

  • Recurring stress or psychological factors.

    Sometimes the mere thought that a food may make you sick actually does. The reason for this is not fully understood.

One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself, such as peanuts, but to a substance or ingredient used in the preparation of the food. This is especially true of foods containing lactose, wheat or sulfites.

Risk Factors
Several factors may put you at greater risk of developing a food allergy:

  • Genetic disposition.

    You may inherit a tendency toward food allergies. If one of your parents has a food allergy, you're twice as likely to develop one.

  • Age.

    About 70 percent of food allergies develop in people younger than 30. The reason: As you grow older your digestive system matures, and your body is less likely to absorb food or food components that trigger allergies. Although you can have food allergies at any age, children are 10 times more likely to have a food allergy than adults. Fortunately, children typically outgrow allergies to milk, wheat and eggs by about age 6. Severe allergies and allergies to nuts and shellfish are more likely to be lifelong. Individuals of all ages are likely to lose sensitivities to milk, eggs and soy products more quickly than to fish, shellfish, peanuts and walnuts.

  • Asthma.

    If you have asthma, you may be sensitive to preservatives containing sulfites. Sulfites, used as a preservative, are present in wines, fresh and dehydrated fruits, seafoods, maraschino cherries, and some soft drinks. Sulfites also are used to preserve lettuce at some salad bars in the Canada, the United States and other countries.

Should I see my doctor?
If you experience worsening symptoms every time you eat a certain food, see your doctor or allergist. If possible, see your physician when the allergic reaction is occurring. This will aid in making a diagnosis.

Emergency treatment is needed immediately if you develop any symptoms of anaphylactic shock.

Screening and Diagnosis
The following may help your doctor determine whether you have an actual food allergy:

  • A history of your symptoms — which foods, and how much, seem to cause problems — and whether you have a family history of food allergies.
  • A food diary of your eating habits, symptoms and medication use.
  • A physical examination to further identify or exclude other medical problems.
  • Skin prick tests using food extracts to determine your reaction, or a blood test that measures IgE antibody. Neither of these tests is 100 percent accurate.
  • Eliminating suspect foods.( See the elimination diets found elsewhere on this site) For a week or two, you may be asked to eliminate suspect foods and add the items back into your diet one at a time. This process can help link symptoms to specific foods. However, this is not a foolproof method. Psychological factors as well as physical factors can come into play. For example, if you think you're sensitive to a food, a response could be triggered that may not be a true allergic one. If you've had a severe reaction to foods, this method cannot be used.

Be sure to avoid so-called cytotoxic testing and symptom provocation-neutralization testing, in which a dose of food extract is placed under your tongue. These tests are costly and unreliable in detecting food allergies.

For a severe reaction to a food allergy, you may need an emergency injection of adrenaline (epinephrine) and a trip to the emergency room.

If a reaction to certain foods is an annoyance, but not life-threatening, your doctor may prescribe antihistamines to block the symptom-producing release of histamine by your immune system. Creams may provide relief of skin reactions.

The best way to prevent an allergic reaction is to know and avoid foods that cause symptoms. Some people may be merely inconvenienced by this, but others may find it a greater hardship. For instance, if beans are a staple part of your diet, it can be a challenge to come up with a substitute that has equal nutritional value. Also some foods — when used as ingredients in certain dishes — may be well hidden. This is especially true in restaurants and in other social settings.

If you know you have a food allergy, follow these steps to avoid an allergic reaction or to know what to do in case of one:

  • Know what you are eating and drinking. Be sure to read food labels.
  • If you have already had a severe reaction, wear an alert bracelet or necklace.
  • Talk with your doctor about carrying emergency medications.
  • If you have asthma, be sure to ask if sulfites have been added to foods when dining in restaurants. When shopping for foods, check labels for the terms sodium bisulfite , potassium bisulfite , sodium sulfite , sulfur dioxide and potassium metabisulfite .

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