What are the causes and risk factors of food allergy?

Food allergy happens when the body's immune system responds in a negative way to proteins in foods. The immune system’s usual job is to protect us from germs, but in this case the response is not helpful. There are two ways that the immune system might cause food allergy. One way is by creating a protein called IgE antibody that recognizes the food protein and triggers a swift allergic response.

The symptoms of this kind of food allergy usually happen soon after the food is eaten. Typical symptoms include hives that look like mosquito bites, swelling and itching of the skin; gut symptoms such as nausea, vomiting and diarrhea; breathing symptoms that could be severe including trouble breathing; and potentially blood circulation can be compromised leading to dizziness, confusion or fainting. In its most severe form, anaphylaxis, we experience a severe allergic reaction that can be fatal.

Another way the immune system causes problems is more insidious. Different immune cells might respond against food protein in a persistent and chronic way leading to persistent skin rashes or gut problems. These are often more difficult to diagnose because there are many causes of rashes and gut problems. We do not entirely understand why our immune system might cause these attacks. There are theories that the parts of the immune system that cause these problems are also the parts of the immune system that usually fight infections with worms or parasites. We have done a lot to protect our immune system from these and many other types of infections through clean living and some people think that this has left our immune system essentially "looking for a fight." Therefore, our immune system might become misdirected and attack foods as well as other things that cause allergy, such as pollens, animal dander, mold, etc.

There is some evidence that food allergy may be increasing, and there are a variety of theories about why this is so, but no one has clear answers. Theories include: the way that our food is processed potentially making it more easily seen by the immune system; aspects of our diet in general, such as the types of fats we eat; vitamins in our diet; the cleanliness hypothesis mentioned previously; and perhaps introducing foods to babies either too soon or too late for the immune system to act correctly.

Food allergies occur more commonly in people who have, or who have relatives with, allergic conditions such as asthma, hay fever, eczema (atopic dermatitis) and food allergies. Our studies showed that 7 percent of fraternal twins and two-thirds of identical twins share peanut allergy. This tells us that genes (inheritance) plays a big role, but also that environment is also very important in whether a person develops a food allergy.

Louise Goldberg
Nutrition & Dietetics Specialist

Food allergies can be inherited and certainly children with parents or siblings who have food allergies have a higher incidence of having a food allergy themselves; however food allergies can occur for other reasons, as well. If infants are introduced to certain foods too early (e.g., cow's milk before 1 year old), it is possible to cause some damage to their gut, which in turn can make them more sensitive and cause reactions to proteins in other foods. It is important to follow guidelines or talk to your pediatrician and dietitian about when foods are safe to be introduced to children.

Ms. Vandana  R. Sheth
Nutrition & Dietetics Specialist

Food allergies do run in families. If a child has two parents with food allergies, it significantly increases the chances of the child developing food allergies. However, there is an increase in the number of children developing allergies without a family history of allergies.

No one really knows why some people have food allergies and others don’t. Having asthma or eczema increases the chance of having a food allergy. 

Like other kinds of allergies, the tendency to have an allergy to food—although not the specific allergy—is inherited. Not only that, but certain foods—including tree nuts, eggs, wheat, peanuts, fish, shellfish and milk—are frequent troublemakers. Children often have more food allergies than adults do, especially to cow's milk and to peanuts. Infants outgrow many food allergies by the age of four. Allergic reactions to shellfish, tree nuts and fish are more common in adults.

Dr. Michael T. Murray, ND
Naturopathic Medicine Specialist

Food allergy is often inherited. When both parents have allergies, there is a 67 percent chance that the children will also have allergies. Where only one parent is allergic, the chance of a child's being prone to allergies drops from 67 percent to 33 percent. Repetitious exposure to a food, improper digestion and poor integrity of the intestinal barrier are additional factors that can lead to the development and maintenance of food allergy.

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Allergies are a reaction when the body sees something as "foreign." In the case of food allergies, when the food is ingested, the body mistakenly believes it doesn't belong there and mounts a response in an effort to "protect" the body. As a result of this effort, you may experience dry or itchy skin, hives, runny nose, itchy and/or red eyes, shortness of breath, nausea, vomiting or diarrhea, or even swelling of your tongue or throat in more severe reactions. For the most part, the specific cause is a protein that is part of the food.

In general, people who have a lot of allergies are at a higher risk for food allergies. Also, a family history of food allergies increases the risk of developing a food allergy. Children are at a higher risk of food allergies than adults, and they sometimes outgrow their allergies. People with asthma are also at increased risk of developing food allergies.

Dr. Clifford W. Bassett, MD
Allergist & Immunologist

There's no clear-cut, proven explanation for the rise in food allergies, but several theories exist. One is that we're exposing infants and young children to high allergy and/or new foods at earlier ages. Even something as simple as peanut or nuts may be present in various creams, lotions and skin moisturizers, used in infants and young children.

Another concern? We're too clean freak-ish for our own good. Oversanitizing the environment and keeping very young children away from pets, day care, and individuals with colds, for example, may result in a greater risk of allergies, according to the "hygiene hypothesis."

Joan Salge Blake, MS, RD
Nutrition & Dietetics Specialist

A food allergy is an abnormal physical reaction of the immune system in response to the consumption of a particular food allergen. Food allergens are proteins that are not broken down during cooking or by the gastric juices and enzymes in the body during digestion. Because they are not degraded, they enter the body intact, and can cause an adverse immune reaction if the allergen is perceived as a foreign invader.

Doctors wish they knew exactly what causes food allergy. In this video, Jessica Savage, MD, Clinical & Laboratory Immunologist at Brigham and Women's hospital explains the many factors that lead to food allergies.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.