A food allergy (Allergy Food) occurs when the body’s immune system sees a certain food as harmful and reacts by causing allergic symptoms. Foods that cause allergic reactions are allergens. There are different types of allergic reactions to foods:
- Immunoglobulin E (IgE) mediated. The body’s immune system makes antibodies called immunoglobulin E (IgE). These IgE antibodies react with a certain food and cause symptoms. In the US, the most common causes of food allergy are these eight foods:
- Tree Nut
- Shellfish (crustaceans)
Many people who think they are allergic to a food may actually be intolerant to it. Some of the symptoms of food intolerance and food allergy are similar, but the differences between the two are very important. If you are allergic to a food, this allergen triggers a response in the immune system. Food allergy reactions can be life-threatening, so people with this type of allergy must be very careful to avoid their food triggers.
Being allergic to a food may also result in being allergic to a similar protein found in something else. For example, if you are allergic to ragweed, you may also develop reactions to bananas or melons. This is known as cross-reactivity. Cross-reactivity happens when the immune system thinks one protein is closely related to another. When foods are involved it is called oral allergy syndrome (OAS).
Food allergy can strike children and adults alike. While many children outgrow a food allergy, it is also possible for adults to develop allergies to particular foods.
Food Protein-Induced Enterocolitis Syndrome (FPIES), sometimes referred to as a delayed food allergy, is a severe condition causing vomiting and diarrhea. In some cases, symptoms can progress to dehydration and shock brought on by low blood pressure and poor blood circulation.
Much like other food allergies, FPIES allergic reactions are triggered by ingesting a food allergen. Although any food can be a trigger, the most common culprits include milk, soy and grains. FPIES often develops in infancy, usually when a baby is introduced to solid food or formula.
Eosinophilic (ee-uh-sin-uh-fil-ik) Esophagitis (EoE) is an allergic condition causing inflammation of the esophagus. The esophagus is the tube that sends food from the throat to the stomach. Most research suggests that the leading cause of EoE is an allergy or a sensitivity to particular proteins found in foods. Many people with EoE have a family history of allergic disorders such as asthma, rhinitis, dermatitis or food allergy.
Food Allergies Diagnosing
Diagnosis is usually based on a medical history, elimination diet, skin prick test, blood tests for food-specific IgE antibodies, or oral food challenge.
For skin prick tests, a tiny board with protruding needles is used. The allergens are placed either on the board or directly on the skin. The board is then placed on the skin, in order to puncture the skin and for the allergens to enter the body. If a hive appears, the person will be considered positive for the allergy. This test only works for IgE antibodies. Allergic reactions caused by other antibodies cannot be detected through skin prick tests.
Skin prick testing is easy to do and results are available in minutes. Different allergists may use different devices for skin prick testing. Some use a “bifurcated needle”, which looks like a fork with 2 prongs. Others use a “multi-test”, which may look like a small board with several pins sticking out of it. In these tests, a tiny amount of the suspected allergen is put onto the skin or into a testing device, and the device is placed on the skin to prick, or break through, the top layer of skin. This puts a small amount of the allergen under the skin. A hive will form at any spot where the person is allergic. This test generally yields a positive or negative result. It is good for quickly learning if a person is allergic to a particular food or not, because it detects allergic antibodies known as IgE. Skin tests cannot predict if a reaction would occur or what kind of reaction might occur if a person ingests that particular allergen. They can however confirm an allergy in light of a patient’s history of reactions to a particular food. Non-IgE mediated allergies cannot be detected by this method.
Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed food reactions.
Blood testing is another way to test for allergies; however, it poses the same disadvantage and only detects IgE allergens and does not work for every possible allergen. RAST, RadioAllergoSorbent Test, is used to detect IgE antibodies present to a certain allergen. The score taken from the RAST test is compared to predictive values, taken from a specific type of RAST test. If the score is higher than the predictive values, there is a great chance the allergy is present in the person. One advantage of this test is that it can test many allergens at one time.
Blood tests are another useful diagnostic tool for evaluating IgE-mediated food allergies. For example, the RAST (RadioAllergoSorbent Test) detects the presence of IgE antibodies to a particular allergen. A CAP-RAST test is a specific type of RAST test with greater specificity: it can show the amount of IgE present to each allergen. Researchers have been able to determine “predictive values” for certain foods. These predictive values can be compared to the RAST blood test results. If a persons RAST score is higher than the predictive value for that food, then there is over a 95% chance the person will have an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that food. Currently, predictive values are available for the following foods: milk, egg, peanut, fish, soy, and wheat. Blood tests allow for hundreds of allergens to be screened from a single sample, and cover food allergies as well as inhalants. However, non-IgE mediated allergies cannot be detected by this method. Other widely promoted tests such as the antigen leukocyte cellular antibody test (ALCAT) and the Food Allergy Profile are considered unproven methods, the use of which is not advised.
Food challenges test for allergens other than those caused by IgE allergens. The allergen is given to the person in the form of a pill, so the person can ingest the allergen directly. The person is watched for signs and symptoms. The problem with food challenges is that they must be performed in the hospital under careful watch, due to the possibility of anaphylaxis.
Food challenges, especially double-blind placebo-controlled food challenges (DBPCFC), are the gold standard for diagnosis of food allergies, including most non-IgE mediated reactions. Blind food challenges involve packaging the suspected allergen into a capsule, giving it to the patient, and observing the patient for signs or symptoms of an allergic reaction.
The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will review the patient’s history and the symptoms or reactions that have been noted after food ingestion. If the allergist feels the symptoms or reactions are consistent with food allergy, he/she will perform allergy tests.
Additional diagnostic tools for evaluation of eosinophilic or non-IgE mediated reactions include endoscopy, colonoscopy, and biopsy.
Breastfeeding for more than 4 months prevents atopic dermatitis, cow milk allergy, and wheezing in early childhood. Early exposure to potential allergens may be protective.
In order to avoid an allergic reaction, a strict diet can be followed. It is difficult to determine the amount of allergenic food required to elicit a reaction, so complete avoidance should be attempted. In some cases, hypersensitive reactions can be triggered by exposures to allergens through skin contact, inhalation, kissing, participation in sports, blood transfusions, cosmetics, and alcohol.
Food Allergies Treating
There is currently no cure for food allergy, but there are many promising treatments under investigation. Avoidance, education and preparedness are the keys to managing food allergy.
While exposure to airborne food allergens (e.g., from cooking vapors) usually does not result in anaphylaxis, it can cause a runny nose and itchy eyes similar to a reaction from coming in contact with pollen. However, eating even a small amount of the food, such as that left on cooking utensils or from a food processing facility, can cause a life-threatening reaction. This is why reading the ingredients on food labels and asking questions about prepared foods are an essential part of avoidance plans.
People with food allergy should always carry auto-injectable epinephrine to be used in the event of an anaphylactic reaction. Symptoms of anaphylaxis may include difficulty breathing, dizziness or loss of consciousness. If you have any of these symptoms in the context of eating, use the epinephrine auto-injector and immediately call 911. Don’t wait to see if your symptoms go away or get better on their own.