Table of Contents
Food Allergies Definition
Hypersensitivity reactions to consumed foods. Food allergies affect about nine million Americans, two thirds of them children under the age of six. Allergies to peanuts, milk, wheat, shellfish, strawberries, and eggs are among the most common. Some people are allergic to preservatives or other substances used to prepare foods. Children tend to outgrow many food allergies; however, many adults develop food allergies later in life.
Unpleasant responses-such as STOMACH irritation, FLATULENCE (intestinal gas), and episodes of DIARRHEA-to certain foods are common but are not necessarily food allergies. An ALLERGY results in the activation of antibodies that triggers a HYPERSENSITIVITY REACTION, an excessive IMMUNE RESPONSE in which the IMMUNE SYSTEM responds to a particular food as though it were a harmful substance. The COMPLEMENT CASCADE floods the blood circulation with antibodies, mast cells release HISTAMINE and PROSTAGLANDINS, and various types of leukocytes mobilize to attack the ALLERGEN.
Though some symptoms may be the same-such as stomach upset and diarrhea-the difference between food intolerance and food allergy can literally be life threatening: ANAPHYLAXIS, the most severe kind of hypersensitivity reaction, is an ever-present danger with food allergies. Of particular concern are ingredients that may not be obvious, such as peanut oil or soy, and may be present in processed foods as cross-contaminants.
Symptoms of Food Allergies and Diagnostic Path
A hypersensitivity reaction to a food produces symptoms that may include
- itching and swelling around the face, on the lips, and in the MOUTH
- nasal congestion
- wheezing or difficulty BREATHING
- sensation of a lump in the throat
- gastrointestinal pain (resulting from swelling in the intestinal mucosa)
- moderate to extensive diarrhea
More generalized symptoms such as SKIN rash, hives (URTICARIA), and ANGIOEDEMA are also possible. Symptoms may occur within minutes to 2 hours after eating the food. Anaphylaxis may develop with any hypersensitivity reaction, even when previous reactions have been mild.
ANAPHYLAXIS is a medical emergency that requires immediate treatment from a doctor. Tingling and swelling of the lips, tongue, and THROAT 20 to 60 minutes after eating a food for which there could be an allergy are possible indications of anaphylaxis.
When there is a clear connection between a specific food and a hypersensitivity response, identifying the allergen is fairly straightforward. When the connection is not clear, the diagnostic path can be arduous and may include
- blood tests to measure IMMUNOGLOBULIN E (IgE) levels
- ALLERGY TESTING with suspect substances
- elimination diet
The elimination diet involves removing suspected foods or foods that are common allergens from the diet, usually for two weeks, and then reintroducing them one at a time until symptoms recur. The last food reintroduced is the likely allergen. An elimination diet is appropriate only for people who have mild to moderate hypersensitivity reactions. The risk for anaphylaxis is too great to use the elimination diet approach in people who have had severe allergy symptoms such as wheezing, breathing difficulty, or urticaria (hives). No single diagnostic approach works for all food allergies; diagnosis becomes a process of drawing conclusions based on symptoms.
Common Food Allergies
|COMMON FOOD ALLERGIES|
|peanuts||shellfish (lobster, shrimp, crab)|
|tree nuts (almonds, cashews, walnuts, pecans)||wheat (including flour)|
Treatment Options and Outlook
A moderate hypersensitivity reaction may require treatment with ANTIHISTAMINE MEDICATIONS; a serious reaction may require a course of oral CORTICOSTEROID MEDICATIONS to halt the immune response and relieve the discomfort of the symptoms. Many hypersensitivity reactions to foods produce mild symptoms that go away without treatment. A doctor should evaluate symptoms that do not improve within a few days.
The most effective long-term treatment is to avoid the allergen. This is not always as easy as it sounds because often variations of the allergen are ingredients in prepared or baked foods. Peanuts, eggs, milk, soy, and wheat are common in many foods. Cross-contamination is also a concern, particularly among processed foods manufactured in facilities that use various ingredients in different products. An ice cream manufacturer may make a flavor that has nuts, for example, and then use the same equipment to make a flavor that does not have nuts.
Even residue not visible to the eye can be sufficient to cause a hypersensitivity reaction in someone who is highly allergic. Labels on packaged foods include information about whether the product comes from a facility in which cross-contamination is possible. People who have food allergies must ask about obvious as well as hidden ingredients when eating away from home.
DESENSITIZATION (allergy shots) is a therapeutic option for people who have allergies to foods that are especially common or who have severe hypersensitivity reactions. Though it takes up to two years for desensitization to reach its maximum effectiveness, most people notice a reduced hypersensitivity reaction within six months.
Risk Factors and Preventive Measures
People who have other allergies or who have family members who have food allergies are more likely to develop food allergies. There are no measures to prevent allergies, food or otherwise. Identifying and avoiding foods that cause hypersensitivity reactions are the most effective methods for preventing those reactions and their unpleasant symptoms. Many people who have food allergies are able to manage them by carefully reading product labels and asking about ingredients when eating away from home.