What Is and What Is Not a Food Allergy?
A food allergy (Gk. allon = different, strange; ergon= activity) is an exaggerated reaction of the immune system to certain food substances otherwise not harmful for the man. These substances, when triggering an allergy, are called allergens. Practically any food may contain substances that can act as allergens; most of people with a food allergy are allergic to fewer than four foods at a certain time, though (5). Allergic reaction involves production of IgE antibodies and releasing of histamine into affected tissues. It is histamine that causes most symptoms like itchy skin or diarrhea.
Food intolerances, like lactose intolerance or fructose malabsorption, are NOT allergies because the immune system (antibodies) is not involved. Gluten intolerance and celiac disease are considered as autoimmune disease, but IgE antibodies and histamine are not released, so they are not food allergies. Various food intolerances determined by finding IgA antibodies in saliva or stool are also not food allergies. Beside obvious symptoms, only the presence of IgE antibodies in the blood confirms an allergy. Typical food allergy symptoms include tingling lips or itchy hives and diarrhea appearing within minutes (or, in delayed reaction, within several hours) after ingesting even a tinny amount of food. In food intolerances, symptoms are mostly confined to gastrointestinal tract.
Disorders, resembling food allergy:
- Food poisoning
- Lactose intolerance
- Fructose malabsorption
- Histamine toxicity
- Reaction to sulfites, monosodium glutamate (MSG) or artificial dyes
- Gluten intolerance, and celiac disease
- Dumping syndrome – rapid gastric emptying
Food Allergies in BABIES and CHILDREN
The following six foods commonly cause allergies in children (1):
- Cow’s milk
- Tree nuts (walnuts, cashews, etc.)
In infants, food allergies, especially to soy and cow’s milk, usually appear as diarrhea in their first days or months. It was found out that exclusive breast feeding may reduce the possibility of developing an allergy in high risk infants (2). Mothers should avoid foods that commonly cause allergies in infants since the allergens may pass into their milk. Children should not be offered cow’s milk until age 1, eggs until age 2, and peanuts, tree nuts, and fish until age 3 (3). Children usually outgrow allergies to soy, wheat, and eggs by the age of six; an allergy to cow’s milk often extends toward school years or far beyond (4). Allergies to peanuts and tree nuts are often life-long.
Children often react to fruit acids with a rash around the mouth – this is NOT an allergy.
Food Allergies in ADULTS
The following four foods commonly cause allergies in adults:
- Tree nuts
- Shellfish, especially shrimps, lobster, crabs, clams, mussels and oysters. Cross reactivity among shellfish is possible, so a person allergic to one shellfish should avoid all shellfish.
Allergies starting in adulthood are often life-long. Food additives (sulfites, monosodium glutamate) rarely cause an allergy (5). Sometimes, food allergies are triggered by exercise. Histamine from some cheeses, wines or spoiled fish may trigger symptoms that mimic food allergy.
Origin of Food Allergies
Food (and other) allergies commonly run in families. It is a predisposition (susceptibility) to develop an allergy, and not an allergy itself that is inherited. If one parent has an allergy, any child has a 50% chance to have it, and 75% chance, if both parents have it. (5).
Food allergens trigger production of specific IgE (immunoglobulin E) antibodies in the blood of a sensitive person (every different allergen triggers slightly different IgE antibody). Antibodies cause release of histamine in the gut, nose, throat, bronchi or skin what results in allergic symptoms.
Symptoms of Food Allergies
Histamine, released in the tissues may result in one or more of the following symptoms appearing within minutes or, in delayed response, several hours after food ingesting (1,5):
- Tingling around the mouth or in the throat
- Swelling of the lips or face
- Runny nose
- Nausea or vomiting
- Feeling of “impending doom” (fear that something bad will happen)
- Itchy skin; bumpy or patchy hives (urticaria) may appear anywhere on the skin
- Chronic symptoms of food allergies are eczema and asthma
- Difficulty breathing, wheezing, blood pressure drop, rapid heartbeat and fainting are symptoms of severe allergic reaction.
- Death rarely occurs in food allergies.
Allergies are common in children, but may appear at any age.
Two Types of Food Allergy
In food allergy with an early response, symptoms appear within minutes to several hours after the meal. In delayed response, symptoms appear 12 to 72 hours after the meal (6). Any food may cause early or delayed response; symptoms may be of the same intensity in both types.
Pollen-Food Allergy Syndrome
Some people with allergy to pollens may get an allergic reaction after eating fresh fruits or vegetables. This is due to cross reactivity of immune system to resembling substances appearing both in pollens and fruits/vegetables. Cooking of fruits/vegetables typically prevents this type of allergic reaction. Foods that may cause pollen-food allergy.
Food Allergy Tests
Different tests to determine food allergy exist:
- In food challenge test, increasing amounts of samples of suspicious foods are given to the patient in certain intervals, and symptoms, which usually develop within 15 minutes, are monitored. Positive response (allergic symptoms) speak for allergy to a tested food. If a strong reaction is expected, a piece of food is put on the lip and a patient is observed for symptoms.
- In elimination diet test, one food a day is eliminated from the diet until symptoms disappear. Then, a suspicious food is introduced again; symptoms reappearance speaks for a food allergy.
- With a skin prick test, an early allergic response is tested. A drop of solution with a sample of suspicious foods is put on the skin of the upper arm and pushed into the skin by prickling the skin with a needle. Red inflammatory rash appearing within 20 minutes around the prick speaks for allergy to tested food.
- With a skin patch test, a delayed allergic response is tested. Several patches with samples of suspicious foods are glued to the back for 72 hours; skin reaction exceeding certain size speaks for food allergy.
- In RAST (RadioAllergoSorbent Test), some blood is drawn and then a sample of food is added to it. If a tested person is allergic to that food his/her blood contains specific IgE antibodies that react with the food sample; this reaction can be detected and speaks for food allergy. This test has many false positive results, so it is done only in individuals with expected dangerous reaction to skin tests, and in babies, in whom skin tests are not reliable. The test is expensive; results can be expected within a week.
- Blood eosinophils (a type of white blood cells) are usually (but not always) elevated in allergies so, together with IgE antibodies, they speak for an allergy but do not confirm it. Blood eosinophils may be also elevated in some parasites, like giardia or intestinal worms, certain blood diseases and in some other disorders.
Prevention and Treatment of Allergies
To date, there is no known cure for food allergies. An allergic person should avoid even small amounts of allergy-triggering foods. Cooking, in general, does not make foods non-allergenic, but it can make a certain food less or sometimes more allergenic. Symptoms of a mild allergy can be eased by over the counter (OTC) antihistamine pills but in severe allergic reaction an intramuscular injection of adrenalin is needed. Persons with severe food allergies should carry a warning bracelet and an anti-allergy kit with adrenalin (epinephrine) injector (“epi-pen”). Drugs should be always taken after an allergic reaction and not before eating since they have no protection value.
- Causes of Diarrhea After Eating
- Loose Bowel Movements – Diagnosis from Medical Symptoms
- Hair Dye Allergies
- Allergy Headache
- Mold Allergy
- House Dust Allergy
- Food allergies in children (aaaai.org)
- Breastfeeding may prevent food allergies in children (children.webmd.com)
- Infants – foods to avoid to prevent allergies (childrensspecialists.com)
- Milk and egg allergy (medicalnewstoday.com)
- Food allergies in adults (aafp.org)
- Early and late allergic reaction (woodmed.com)
Article reviewed by Dr. Greg. Last updated on January 7, 2012