Learning that you or your loved one has an allergy to a food often sparks a long list of questions. One common question that many families have is “If my child is allergic to one food, what else might they be allergic to?” Another common question is “Where should I start when either trying new foods or adding foods back to my diet?” If you have these questions, you are not alone! First, everyone is unique, and there is no substitute for individualized guidance from your healthcare team. But let’s take a look at something called cross-reactivity to help you get the conversation started with your healthcare team to ask these questions.
Identifying a Food Allergy
An allergy to food happens when your immune system overreacts, typically to the protein in the food. For example, children often have a milk allergy, which more specifically an allergy to protein in cow milk. Proteins found in one food can be similar in shape to proteins in other or related foods. When that’s the case, sometimes your immune system cannot tell the difference. The question then is: If you are allergic to one food’s proteins, will you also be allergic to the protein in a related food? The state of being allergic to two foods can be called called “cross-reactivity.” But what does that mean for you?
Food allergies can involve many types of responses. For example, you may get a rash after eating a certain food or a reaction could be life threatening, like anaphylaxis. The most common immune response to a food is when your body makes something called IgE antibodies to the protein of the food allergen. This can cause a variety of physical reactions or symptoms such as skin itching, hives, nausea, vomiting, diarrhea, breathing difficulty such as wheezing or coughing, or the life-threatening reaction called anaphylactic shock.
As you likely know, diagnosis of food allergies is not an easy process. Experts at the Jaffe Food Allergy Institute in New York recommend that diagnosis of food allergies include careful interpretation of a variety of factors. These include physical examination, skin test or RASTs, detailed patient history, and oral food challenges or elimination diets. This extensive testing and variable results are just a few of the many reasons behind the importance of individualized treatment. They also illustrate why there is no substitute for the individual guidance your healthcare team provides.
What is Cross-reactivity?
So where should you start when either trying new foods or adding foods back into your diet? Allergists have researched how likely people with allergies to certain foods are to react to other, related foods. They did this to help other allergists identify related foods of concern as they help families like you. Family allergists may use this data to help determine what advice to give their patients when trying new foods or adding foods back to the diet. If you want to read the review of the clinical data, the full reference is noted below.
In some cases, the data reveals a significant chance of having an allergic reaction (or at least a positive allergy test) to a new food with related proteins. (These are also called homologous proteins, because they have similar shapes.) For example, if you are allergic to cashews, you have a high likelihood to be allergic to pistachios and/or mango.1 There are many families of foods that may be linked, so consult your healthcare provider to determine the extent of your food allergy and the potential for cross-reactivity. As noted above, your healthcare team will tailor guidance for you after evaluating your information and test results.
How to Spot Foods That Might Cause Cross-reactivity?
The table below shows some of the potential cross-reactivity revealed by this research review. An allergist at the Jaffe Food Allergy Institute at the Mount Sinai School of Medicine in New York lead the development of this table. This table is really for clinicians, not patients. Clinicians might use a table like this when considering where you might start when either trying new foods or adding foods back to the diet.
A clinician would look for your known food allergen in the left column. The center column shows foods that contain similar proteins. The column on the right gives an indication of risk of an allergic reaction to one of the foods in the center column. Let’s take the example of a patient allergic to cow milk. The available research shows there is a 92% chance the patient will react (or have a positive allergy test) to goat milk, but only a 4% chance of an allergic reaction to horse (mare) milk.
As always, follow the guidance and recommendations from your healthcare team.
What is the best way to introduce new foods to the diet?
Once your healthcare team helps you make a plan, the next step is trying the foods suggested. Your healthcare team will likely provide you with specific guidance. They may suggest you try certain foods at home, starting with a small amount, waiting a few days before the next food. They may provide specific guidance on how much of the food to eat and how often.
If you’ve had severe allergic reactions to food in the past, they may recommend a more cautious approach. “Oral food challenge” is the name for this type of test. These are done under strict medical supervision (at a doctor’s office) in case of a severe reaction to the food. These usually start with small amounts of the food, gradually increasing the amounts as tolerated. They usually take several hours, as the medical team watches for allergic reactions. Depending on your results, the healthcare team will guide you through trying new foods.
Originally published December 2015 by Ellen Avery, MS, RD, CNSC®
Last updated April 2018 by Rob McCandlish, RDN
Sicherer SH. Clinical implications of cross-reactive food allergens. J Allergy Clin Immunol. 2001;108(6):881-90.