Some people think that food allergies can cause all kinds of diseases from sneezing, rash to behavior problems, headaches and seizures. The typical food allergy however presents with nausea, vomiting, hives, lip/mouth swelling, diarrhea, possibly faintness within minutes of exposure to the culprit food. For typical food allergies the culprit food in most cases is in the following groups:
- Tree nuts
When people suffer from itchiness of the mouth after exposure to certain vegetables or fruits it is often caused by substances on the surface that cause itching (tyramine, histamine), but no serious allergies. Itching and swelling of the mouth may also be due to “oral allergy syndrome”. Oral allergy syndrome occurs in patients who have an allergy to tree pollen (birch), ragweed or mugwort (two common weeds). A protein, which occurs in the pollen as well as in the fresh fruit or vegetable (particularly apple, pears, potato, carrots, melons, celery). These allergens break down when the food gets cooked, baked, boiled or altered in other ways. Therefore they only cause problems in the raw form and usually don’t lead to life threatening allergy episodes. Oral allergy syndrome affects about 50-70% of all adults with tree pollen allergy.
There are food allergic reactions which develop slower and are not the immediate type typical reaction. An example of that is eczema. It may take a couple of days until the skin reactions occur or disappear if a food is introduced or omitted from the diet. That makes it much harder to find the food in question.
Food reactions can also be the cause for reflux caused by eosinophilic esophagitis and certain intestinal problems such as celiac disease.
How to test for food allergies:
- After taking a good history and examination, the allergist usually performs skin testing for the foods in question. A small amount of extract gets introduced by scratching into the skin. After 15 minutes the test can be interpreted by an allergist.
- A blood test for allergies can also be performed and can be helpful to follow the level of allergy to food over the years. It can aid in monitoring if a child outgrows a food allergy.
- Oral allergy syndrome can be diagnosed by testing for the pollen allergy and testing with fresh fruits or vegetables in question.
- For the slower food allergies like eczema or the intestinal disorders, testing can be difficult. Some allergists do patch testing for foods, but there is not standardized test. It is mainly performed at Academic centers. A trial of food avoidance with step-by-step reintroduction can be helpful in diagnosis as well.
Why do I have food allergy?
If both your parents have allergies, you have about a 75 percent chance of being allergic. If one of your parents is allergic, or if one of your relatives from either side has allergies, you have a 30-40 percent chance of having some form of allergy yourself. If neither parent has allergy, the chance is only 10-15 percent.
The amounts of a food or a kind of food you eat, and how often you eat, it may be important to why you become food allergic.
Which foods are most likely to cause allergy?
Almost any food can start an allergy. Peanuts, tree nuts and shellfish often cause severe food allergies.
Someone allergic to a food may also react to related foods. A person allergic to walnuts may also react to pecans. Persons allergic to shrimp may also react to crab and lobster. A person allergic to peanuts may have problems with soy, peas or certain kinds of beans.
Most food allergy patients only react to one or two foods. Someone allergic to pecans may not have to stop eating all nuts. This should be discussed with your allergist.
For additional resources on food allergies, visit the Food Allergy and Anaphylaxis Network. For the Guidelines for the Diagnosis and Management of Food Allergy in the United States visit the National Institute of Allergy and Infectious Diseases.