Foods can cause a number of reactions, not all of which are allergic. Anyone can experience an adverse reaction to a food. The types of adverse reactions are as follows:
Adverse Reactions to Foods
Food Intolerance – where the immune system is not involved in the reaction
- Food poisoning
- Idiosyncratic reactions to food
- Anaphylactoid reactions (they act like anaphylaxis but there is no allergy-IgE antibody involved)
- Pharmacologic reactions
Food Allergy - when the immune system is involved in the reaction
- IgE mediated (classic allergy- tests are available) Non-IgE mediated
- Type III immune response- a serum sickness like reaction
- Type IV immune response- a contact dermatitis type reaction
Food Allergy – Facts and Figures
- Food intolerance accounts for 80% of all adverse reactions to food.
- Food allergy accounts for 20% of all adverse reactions to food.
- Food allergy is most common in infants and young children where the incidence is 3%; thereafter the incidence decreases to 1% of the population.
- Food allergy is suspected in 30% and actually proven in only 3%.
- Allergy to cow’s milk, eggs, wheat, and soy may be outgrown by age 2-4 years.
- Allergy to peanut, shellfish, and tree nuts is usually lifelong.
Allergic Reactions to Foods
Foods can trigger a variety of reactions involving the immune system. The list includes the following:
- Anaphylaxis and associated syndromes
- Systemic anaphylaxis
- Local anaphylaxis
- Exercise-induced anaphylaxis
- Urticaria and angioedema
- Atopic dermatitis
- Gastrointestinal reactions
- Respiratory tract problems
Systemic anaphylaxis can be caused by any food. There tends to be associations with different ages. An infant or young child may tend to have anaphylaxis to peanuts, eggs, cow’s milk, and fish. Adults have a slightly different list that still include peanut and fish, but also includes shellfish and tree nuts.
Local anaphylaxis is a misnomer- it is the complaint of localized swelling of the mouth, an itchy tongue, or hoarseness. It has been seen in association with fruits and vegetables. This 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.
The food associated exercise-induce anaphylaxis syndromes are rare and confusing. The affected patient may be able to exercise without any problems and will be able to 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. The thought of vigorous exercise after eating some of these foods is an issue by itself!
Atopic dermatitis may also have a food as a contributor to the severity of the disease. The food may not be the only trigger. According to our colleagues in the Atopic Dermatitis Signature Center Clinic, there can be 25 different triggers, some of which are allergy.These patients react to a variety of stimuli, but identifying a food trigger may help overall control. This is most frequently seen in infants and young children. It usually appears after the 3rd month of life. The cause-effect relationship of ingestion and skin symptoms is usually not obvious to the parents. Six foods account for the majority of cases- egg, wheat, soy, milk, peanut, and fish. Current food allergy guidelines suggest that egg sensitivity may be the most important single food aggravating the condition. Although the 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 it is not clinically relevant. Oddly enough we get better results from the negative as opposed to the positive skin test. The negative predictive value is 6%- if the test is negative there are only 6 chances out of 100 (6%) that the food is the cause. A positive skin test is a 50/50 proposition. It may or may not help. We use it as a starting point to direct avoidance diets.
Urticaria and angioedema may have a food as the trigger. This is usually seen in the acute cases- hives that have been present for only a few days. Chronic urticaria and the deeper tissue swelling known as angioedema are rarely if ever due to foods. The history is helpful. Skin testing has a low rate of return (please see the section on hives).
There are a variety of food reactions that affect the gastrointestinal tract. The list includes:
- Oral allergy syndrome (mentioned above)
- Gastrointestinal anaphylaxis- severe diarrhea and vomiting leading to shock
- Eosinophilic syndromes- esophagitis, gastritis, colitis
The eosinophilic gastrointestinal syndromes have a food associated with the condition unfortunately, the reaction may not one that is 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 what 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.
Food and respiratory illnesses has been a very hot topic. For years it was believed that food, especially cow’s milk was a major cause of nasal symptoms and a cause of asthma. There are many recent studies that have decreased the role of foods in respiratory illnesses. In large series of observations on what happens to children when undergoing a food challenge, isolated wheezing was seen in only 2% of those who thought a food was involved. Milk is the food we hear about in the clinic, however some recent rather exciting work has implicated another food- egg. Eggs did not cause over wheezing when ingested. They were however associated with increased airway nonspecific reactivity. They made it easier for other things to trigger an event. More work is needed in this area.
Non-allergic Reactions to Foods
There has always been concern that foods were related to headaches. This may be the case, however the mechanism is not an allergic one. They do not cause headaches through an immune mechanism. Skin testing cannot predict these reactions. Remember, foods may contain pharmacologic agents that may 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 are due to food allergy. This is an area that has been extensively evaluated. The behavior problems are not mediated by type I immune mechanisms. They are not IgE mediated problems. Skin tests and blood tests for allergy only reveal that the patient is making IgE to that product. The test does not necessarily mean that the child is allergicThe illnesses due to IgE reactions are well defined. These would be the clinical conditions for which allergy tests may be of help.
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 test materials available for testing these products, nor are there any blood tests.
The Diagnosis of Food Allergy
The history is most important. The nature of the reaction, the frequency and importantly the cause-effect relationship needs to be sorted out. The physical examination also is necessary to direct the next step- testing. Skin tests or blood tests are done to confirm the suspected diagnosis. The skin test by itself does not make the diagnosis. The skin test is an adjunct. Challenges are the gold standard for the diagnosis. Once the suspected food is identified, the therapeutic plan is then formulated.
Treatment of Food Allergy
Nothing will work better than avoidance. Families need to be shown how to read food labels and how to identify the variety of ways a food can be labeled. In our clinic we go over the many ways of identifying eggs, or milk, or soy in a product. Families are advised to find products that are free of the allergen and use them. We also try to have them enroll in the Food Allergy Network. This is a fantastic organization. They provide warnings about contamination issues. Help with food substitutes and offer educational material to help schools, playgroups, and relatives understand the problem. The most important rule regarding avoidance is that if you don’t know, don’t eat it.
If anaphylaxis is the issue- epinephrine is made available and instructions are given as to when and how to use it. Trainer devices are available in our clinic. When a family leaves with a prescription for epinephrine, they also leave knowing how to use it. If needed the trainer devices are sent home so others who are in contact with the child are comfortable with its use.
Medical alert bracelets help. They serve as a warning to those who may offer potentially life-threatening treats.
There are no drops or shots that have been shown to work and are safe. There is some very exciting work going on regarding immunotherapy for food allergy. The foods have included hazelnut, milk, egg, and peanut. The results are encouraging, however the study populations are very small, The recent guidelines for food allergy (2010) do not recommend immunotherapy for food allergy at this time.We can help with avoidance and treat the episodes.
Repeat skin testing can be done after a year or two of avoidance. If there has been strict avoidance yet the skin test is still positive a blood test for the food allergy, once upon a time called RAST but now called specific IgE is done. The specific IgE values to a food can be used as a predictor for a food reaction. If the value is below a critical cut-off value, a challenge can be offered. Challenges are dependent upon the nature of the reaction.
We have helped with the establishment of a food allergy support group in the Evansville area. The credit goes to the mother of our patient who has done a wonderful job in running this group.
The Food Allergy Network is also a wonderful group.
Food Allergy Network
10400 Eaton Place
Fairfax, Virginia 22030-2208