Studies demonstrate that 1 in every 13 U.S. children has a food allergy, a reproducible, adverse reaction to a food that is caused by a type of immune reaction to an allergen in that food. Usually, a food allergen is a small fragment of protein from the food that in susceptible individuals is identified by the body as harmful and that elicits an allergic reaction by the immune system. Interestingly, the first exposure to a food does not cause an allergic response, but it sensitizes susceptible individuals to the food by causing the immune system to produce antibodies (immunoglobulin E [or IgE]) that are specific to the food allergen. When the food is consumed again the food allergen binds to these antibodies, which stimulates immune cells to release histamine and other chemical substances that trigger an allergic reaction. (INFOGRAPHIC 18.10)

Question 18.7

The most common food allergies are to cow’s milk, eggs, peanuts, tree nuts, wheat, soy, fish, and crustacean shellfish. For individuals allergic to one or more of these foods, consuming even minute amounts can be immediately life-threatening. Food allergens can cause gastrointestinal reactions including “itchy” mouth, nausea, vomiting, abdominal cramps, and diarrhea; skin reactions such as hives, swelling, itchiness, and flushing; respiratory problems like wheezing, coughing, and runny or itchy nose; and most severely, they can cause anaphylaxis or anaphylactic shock, a massive immune reaction that can result in death if not treated with injected epinephrine (adrenaline). Although symptoms typically appear within two hours of exposure to a food allergen, allergic reactions can also be delayed. Younger children with delayed allergic reactions most commonly experience heartburn, vomiting, bloody stools, and poor growth. (INFOGRAPHIC 18.11)

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Although most adverse reactions or sensitivities to food are attributed to allergies, many food-induced symptoms are not allergic in nature and instead may be caused by a food intolerance, a reproducible adverse reaction to a food that is not a direct result of an antibody (IgE) dependent immune response. Food intolerances can induce allergy like gastrointestinal and respiratory symptoms and often appear within a few hours of eating the food, but they are not life-threatening and are the result of different bodily mechanisms. Lactose intolerance, for example, is caused by reduced levels of the digestive enzyme lactase in the gastrointestinal tract, but there are other potential causes for food intolerance. Celiac disease is also classified as a food intolerance and not a food allergy because it does not involve the production of allergen-specific antibodies. Rather it is caused when immune cells directly attack the lining of the small intestine in the presence of gluten, a protein found in wheat, rye, barley, and many processed foods.

How can parents distinguish between food allergies and intolerances? In general, the best way to diagnose mild food allergies is through immunologist-led, double-blind, placebo-controlled oral food challenges in which kids are exposed to suspected food allergens and to “fake” allergens at alternating times, without knowing which is which, while being closely monitored. In a 2013 study, Dutch researchers administered this kind of food challenge to 116 infants and toddlers believed to have cow’s milk allergies and found that only one-third of them were truly allergic. On top of that, some allergies naturally resolve over time. About 80% of children, for instance, outgrow cow’s milk allergies, and most also outgrow egg allergies. This could be because the gastrointestinal tract matures to become less permeable with age, making it less likely that an allergen will be able to penetrate the lining of the intestine and initiate an immune response. Other scientists contend that food allergy risks go down with increased exposures to allergens.

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Some food allergies are diagnosed in children and persist into adulthood. Allergies to peanuts and tree nuts are good examples of this category. There are some allergies, however, that tend to be diagnosed more commonly in adults. For example, estimates of fish allergy appear to be more than twice as high in adults than in children and allergy to crustaceans was five times more common in adults. Furthermore, food allergies can develop at any point in a person’s life.

Why are allergies becoming more common? Some contend that heightened awareness among the public and health care providers translates to increased recognition and diagnosis of allergies. Another theory that was already mentioned was the hygiene hypothesis—the idea that less exposure to dirt and germs interferes with the normal maturation and regulation of the immune system. Changes in food manufacturing and processing could also play a role, in that foods are prepared differently now than they used to be. For instance, peanuts used to be boiled, but now they are roasted. Some scientists also theorize that inadequate intake of certain nutrients, like vitamin D, omega-3 fatty acids, and folate, may contribute to the rise of food allergy in children. Finally, the timing at which foods are introduced to kids could be important: Many parents delay the introduction of allergenic foods to their children, but research suggests that delaying introduction beyond a certain point may actually be detrimental.

Although there are no food allergy “cures,” it is now getting easier for families to avoid foods that elicit allergic reactions. As a result of the Food Allergen Labeling and Consumer Protection Act of 2004, food manufacturers and packagers have to declare the presence of major food allergens on food packages.

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The Academy of Nutrition and Dietetics suggests that parents read food labels carefully; that they educate family members, caregivers, and teachers about allergy severity; and that they teach children about their allergies at a young age. It may also help for parents of children with food allergies to consult with a registered dietitian to develop a healthy eating plan that avoids allergens.

The Academy of Nutrition and Dietetics has published tips for parents who want to minimize the risk of food allergies in their children. They suggest exclusive breastfeeding for at least four months during infancy, which decreases the risk of atopic dermatitis, cow’s milk allergy, and wheezing compared with the use of cow’s milk–based formula. (Soy formula does not seem to affect allergy risk.) The organization also recommends against introducing solid foods before four to six months of age. That said, avoiding common allergens such as fish, eggs, and peanuts during pregnancy, breastfeeding, or beyond the age of four to six months in infants does not seem to be protective. In fact, there is growing evidence that the introduction of potentially allergenic foods while the infant is still receiving the majority of calories from breast milk reduces the risk of subsequent allergies.

In light of the growing evidence in support for the hygiene hypothesis, can parents do anything else, lifestyle-wise, to protect their kids against allergies and other immune conditions? No one advocates that kids should be raised in unsanitary conditions, but there may be other ways to help “prime” kids’ immune systems to make them healthier and less susceptible to immune problems. “Be closer to nature,” Kondrashova suggests—don’t avoid contact with pets, grass, soil, and farms. In other words, let kids be kids. Don’t deny them the fun of getting dirty once in a while. As paradoxical as it might seem, dirt and germs could, ultimately, make children healthier for life.