Foods can cause a number of reactions, but not all reactions are allergic. Anyone can experience an adverse reaction to a food. We differentiate the types of adverse reactions below.
The Guidelines for the Diagnosis and Management of Food Allergy in the United States (2010) state that for a food to cause an allergic reaction the food would cause:
- Classic allergic symptoms with every exposure.
- Classic allergic symptoms regardless of the amount of the exposure.
- A reaction that occurs within hours of exposure.
If medical history shows that sometimes there are no reactions to the specific food, then it is not an allergy and the reaction may be due to something else. To indicate a food allergy, the reaction will always occur, occur quickly and occur even in response to a small amount of the food.
Reactions where the immune system is involved in the reaction:
- IgE mediated. This means the allergy occurs because of production of specific IgE antibodies directed against the antigen. This type is the classic allergy and tests can be used to screen for this type of allergy.
- Non-IgE mediated. This type of allergy is not as clearly defined as the IgE mediated allergy. The reaction time to the allergen and symptoms differ and may be delayed. There may be no tests for foods that react in this way.
- Type III immune response is a serum sickness-like reaction.
- Type IV immune response is a contact dermatitis-type reaction.
Food intolerances tend to be dose-related. A little bit is tolerated, but more causes symptoms. Reactions where the immune system is not involved in the reaction:
- Food poisoning
- Idiosyncratic (uncommon or unusual) reactions to food
- Anaphylactoid reactions. This is similar to anaphylaxis, but there is no allergy-IgE antibody involved.
- Pharmacologic reactions (due to chemicals naturally present in some foods)
Food Allergy Facts And Figures
- Food intolerance accounts for 80 percent of all adverse reactions to food.
- Food allergy accounts for 20 percent of all adverse reactions to food.
- Food allergy is most common in infants and young children where the incidence is 3 percent; in older children and adults, the incidence decreases to 1 percent of the population.
- Food allergy is suspected in 30 percent of the population, but actually proven in only 3 percent.
- Allergy to cow's milk, eggs, wheat and soy may be outgrown by age 2-4 years.
There are four foods that tend to be lifelong food allergies:
- Tree nuts**
*There is a 20 percent chance of outgrowing a peanut allergy.
**There is a 10 percent chance of outgrowing a tree nut allergy.
Allergic Reactions To Foods
Foods can trigger a variety of reactions involving the immune system.
- Systemic anaphylaxis (an extreme reaction to an allergen)
- Local anaphylaxis (an extreme but localized reaction to an allergen)
- Exercise-induced anaphylaxis (symptoms occur typically when an allergen and exercise are combined)
- Hives and angioedema (swelling of deep skin layers)
- Atopic dermatitis (an inflammatory and itchy skin disorder)
- Gastrointestinal reactions
- Respiratory tract problems
Systemic anaphylaxis (an extreme reaction to an allergen) can be caused by any food. This reaction tends to be associated with different allergens at different ages. Infants or young children tend to have anaphylaxis to peanuts, eggs, cow's milk and fish. For adults, the list includes peanuts, tree nuts, fish and shellfish.
Local anaphylaxis is a misnomer—it is the complaint of localized swelling of the mouth, an itchy tongue or hoarseness. This reaction may be associated with fruits and vegetables. This type of reaction is never a serious reaction and is often referred to as the oral allergy syndrome. There seems to be an association between the offending food and the coexistence of pollen allergy. Patients with ragweed sensitivity may have complaints after eating watermelon or bananas. Those with birch tree pollen sensitivity may react to apples, carrots, potatoes and hazelnuts. Our knowledge about the associations of pollens and oral allergy increases each year.
The food-associated exercise-induced anaphylaxis syndrome is rare and confusing. The affected patient may be able to exercise without any problems and eat the suspected food and experience nothing. However, if the triggering food is eaten within a few hours of exercise, there may be anaphylaxis. There are well-documented cases of this occurring after celery, shrimp, oysters, peaches, wheat, chicken and a number of other foods.
Food may contribute to the severity of atopic dermatitis, but the food may not be the only trigger. Atopic dermatitis can have 25 different triggers, some of which are allergy. These patients react to a variety of stimuli, but identifying a food trigger may help with overall control. Atopic dermatitis is most frequently seen in infants and young children. It usually appears after the third month of life. The cause-effect relationship between food and skin symptoms is usually not obvious to the parents. Six foods account for the majority of cases—egg, wheat, soy, milk, peanuts and fish. Current food allergy guidelines suggest that egg sensitivity may be the most important single food aggravating the condition.
Although allergy tests may be positive for a number of foods, it is usually only one that is the culprit. These children show many false positive skin tests to foods, meaning that the positive food is not clinically relevant. Oddly enough, better results come from the negative skin test as opposed to the positive skin test. The negative predictive value is 6 percent. If the test is negative, there are only six chances out of 100 (6 percent) that the food is the cause. A positive skin test only offers a 50/50 chance that the food is the culprit and that information may or may not help. It can be a starting point for trying an avoidance diet.
Hives and Angioedema
Hives and angioedema (swelling of deep skin layers) may have food as the trigger. This is usually seen in acute cases where hives have been present for only a few days. Chronic hives and the deeper tissue swelling known as angioedema are rarely if ever due to foods.
- Oral allergy syndrome (see localized anaphylaxis)
- Gastrointestinal anaphylaxis, which includes severe diarrhea and vomiting leading to shock
- Eosinophilic syndromes such as esophagitis, gastritis and colitis
The eosinophilic gastrointestinal syndromes are associated with food. Unfortunately, the reaction may not be predicted by allergy skin testing. One of the more frustrating aspects of this condition is the lack of any test to determine what the cause truly is and a test that can show resolution or progress over time that is simple, inexpensive, easy to do and entirely safe. Repeat biopsy is done to manage the condition. The immune system is involved in eosinophilic esophagitis, but it does not leave a marker that is easy to use to make any predictions.
Respiratory Tract Problems
For years, food—especially cow’s milk—was believed to be a major cause of nasal symptoms and asthma. Recent studies show food may play a smaller role in respiratory illnesses than previously thought. In a large series of observations of children undergoing a food challenge, isolated wheezing was seen in only 2 percent of those who thought a food was the allergen. Milk is often the food cited; however, recent studies suggest egg may be the culprit. Eggs did not cause wheezing when ingested, but were associated with increased airway nonspecific reactivity. Eggs made it easier for other allergens to trigger an event. More study is required in this area.
Non-Allergic Reactions to Foods
There has always been concern that foods can cause headaches. This may be the case; however, the mechanism is not an allergic one. Foods do not cause headaches through an immune mechanism. Skin testing cannot predict these reactions. Remember, foods may contain pharmacologic agents (naturally occurring chemicals) that can cause headache in susceptible individuals. Prime examples of foods that may cause pharmacologic reactions are:
- Dairy, especially aged cheeses
There is also concern that behavior problems may be tied to food allergy. This is an area that has been extensively evaluated. Behavior problems are not caused by type I immune mechanisms nor are they IgE-mediated problems (problems caused by production of IgE antibodies directed at an allergen). Skin tests and blood tests for allergy only reveal that the patient is making IgE in response to an allergen. The test does not necessarily mean that the child is allergic. The illnesses that are due to IgE reactions are well defined. These would be the clinical conditions for which allergy tests may be helpful.
Food preservatives and dyes have also been an area of concern. Unfortunately, these chemicals do not react by a type I immune response. There are no skin tests or blood tests available for testing these products.
Diagnosing a Food Allergy
Obtaining a medical history and history of response to foods is important. The nature of the reaction, the frequency and a cause-effect relationship needs to be determined. A physical exam is also necessary to direct the next step, which is testing. Skin tests or blood tests help confirm a suspected diagnosis. A skin test by itself does not make a diagnosis. Food challenges also can help confirm diagnosis. Once a suspected food is verified, a treatment plan is made.
Treating a Food Allergy
Nothing works better to treat a food allergy than avoidance. The best tip for avoidance is if you don’t know for sure what is in a food, then don’t eat it. Our staff teaches your family to read food labels and identify the many ways a food can be labeled. In our clinic, we go over ways to identify eggs, milk or soy in a product. We advise families to use products that are free of the allergen. We encourage families to become members of Food Allergy Research and Education (FARE). This organization provides warnings about contamination issues, suggests food substitutes and offers educational material to help schools, playgroups and relatives understand the problem.
If the food allergy causes anaphylaxis or if there is a peanut allergy regardless of the symptoms that occur with peanut ingestion, epinephrine is prescribed. You will receive instructions for when, how and why to use epinephrine, as well as what to do after its use. Trainer devices that teach how to use epinephrine are available in our clinic. Injectable epinephrine prescriptions always come with a trainer device so other family members and caregivers who are in contact with your child can become comfortable with its use.
Medical alert bracelets can help protect your child. They serve as a warning to other parents and adults that certain types of foods can be life threatening to your child.
Currently, there are no medicines for food allergy that have been shown to work and are safe. There is exciting experimental work going on with immunotherapy for food allergy; however, it is not approved for general use. The foods included in immunotherapy experiments include hazelnut, milk, eggs and peanuts. The results are encouraging; however, the study populations are very small. Recent guidelines for food allergy do not recommend immunotherapy for food allergy at this time. Our team can help patients with avoidance and teach how to treat episodes.
More skin tests can be done after a year or two of avoidance. If there has been strict avoidance yet the skin test is still positive, then a blood test for the food allergy—called specific IgE—is done. The specific IgE values to a food can be used as a predictor of a food reaction. If the value is below a critical cut-off value, a food challenge can be offered. The use of a food challenge depends on the nature of the reaction.
You can find additional information about food allergy by accessing the Guidelines for the Diagnosis and Management of Food Allergy in the United States.
There is a food allergy support group in the Evansville area. The credit goes to the mother of a patient who has done a wonderful job running this group. If you are interested in this group, please ask our office staff for more information.
Food Allergy Research and Education (FARE) is also a wonderful resource.
7925 Jones Branch Dr., Suite 1100
McLean, VA 22102