What Is Food Allergy?
Although many people have bad reactions to certain foods, a true food allergy — a reaction triggered by the immune system — isn't as common as you might think. But, the number of people who have a food allergy is growing. About 2 percent of adults and 6 percent of children have a true food allergy. Far more people have food intolerance, unpleasant symptoms triggered by food. Unlike a true food allergy though, a food intolerance doesn't involve the immune system.
This is little consolation if you've had a bad experience with a particular food and fear a recurrence. But it is an important distinction, because a true food allergy — also called a food hypersensitivity — can cause serious problems and even death.
If you have a reaction to a particular food, tell your doctor about it. Tests can help diagnose a food allergy so that you can take steps to avoid a repeat problem.
What is the Causes of Food Allergy
In a true food allergy, your immune system mistakenly identifies a specific food or a component of food as a harmful substance. Your immune system triggers certain cells to produce immunoglobulin E (IgE) antibodies to fight the culprit food or food component (the allergen). The next time you eat even the smallest amount of that food, the IgE antibodies sense it and signal your immune system to release histamine and other chemicals into your bloodstream.
These chemicals cause a range of allergic signs and symptoms. 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.
The great majority of food allergies are triggered by certain proteins in:
- Eggs
- Peanuts
- Fish
- Shellfish, such as shrimp, lobster and crab
- Tree nuts, such as walnuts and pecans
In children, food allergies are also commonly triggered by proteins in these foods:
- Cow's milk
- Wheat
- Soybeans
Chocolate, long thought by some parents to be a culprit among children, seldom is a cause of food allergy.
Food intolerance and other conditions: Not food allergies
Other reactions to food don't involve your immune system or the release of histamine. These reactions aren't true food allergies. Instead, they may be a food intolerance. Because a food intolerance may involve some of the same signs and symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea — people often confuse the two.
If you have a food intolerance, you may be able to 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.
One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself but to a substance or ingredient used in the preparation of the food. For example, sulfite preservatives can trigger asthma signs and symptoms in sensitive people.
Common non-allergy related problems 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. Certain foods may trigger the signs and symptoms of irritable bowel syndrome. You may find that certain foods will cause cramping, constipation or diarrhea. Steer clear of these foods to avoid the symptoms.
- Food poisoning. 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 also can make a toxin that triggers adverse reactions.
- Recurring stress or psychological factors. Sometimes the mere thought of a food may make you sick. The reason is not fully understood.
How is food allergy treated?
Dietary Avoidance: Avoiding the offending allergen in the diet is the primary treatment of food allergy. Once a food to which the patient is sensitive has been identified, the food must be removed from the diet. To do this, patients need to read lengthy, detailed lists of ingredients on the label for each food they consider eating. Many allergy-producing foods such as peanuts, eggs, and milk appear in foods that are not ordinarily associated with them. For example, peanuts often are used as protein supplements, eggs are in some salad dressings, and milk is in bakery products. The FDA requires that the ingredients in a food are listed on its label. People can avoid most of the foods to which they are sensitive if they carefully read the labels on foods and, when in restaurants, avoid ordering foods that might contain ingredients to which they are allergic.
Treating an Anaphylactic Reaction: Patients with severe food allergies must be prepared to treat an anaphylactic reaction. Even those who know a lot about their own allergies can either make an error or be served food that does not comply with their instructions. To protect themselves, people who have had anaphylactic reactions to a food should wear medical alert bracelets or necklaces stating that they have a food allergy and that they are subject to severe reactions. These individuals also always should carry a syringe of adrenaline (epinephrine), obtained by prescription from their doctors, and be prepared to self-administer it if they think they are developing an allergic reaction. They then should immediately seek medical help by either calling the rescue squad or having themselves transported to an emergency room.
Treating other Symptoms of Food Allergy: Several medications are available for treating the other symptoms of food allergy. For example, antihistamines can relieve gastrointestinal symptoms, hives, sneezing, and a runny nose. Bronchodilators can relieve the symptoms of asthma. These medications are taken after a person inadvertently has ingested a food to which he is allergic. They are not effective, however, in preventing an allergic reaction when taken prior to eating the food. In fact, no medication in any form is available to reliably prevent an allergic reaction to a certain food before eating that food.