Outgrowing an Allergy
For as long as she could remember, Carolyn Parmer, now 16, had to bring her own cake to birthday parties. She was allergic to nuts and sesame seeds, and her mother was worried that even the slightest contamination could trigger an allergic reaction.
“When I had allergies, we wouldn’t really eat out a lot because of contamination risk, and if I’d do summer camp or something, I’d have to have my own meal,” Parmer said.
She carried an epinephrine auto-injector with her everywhere and dutifully asked about ingredients in snacks and at sleepovers. Over the years she was monitored by her allergist, Carla Davis, M.D., director of the Food Allergy Program at Texas Children’s Hospital.
At one point during a routine checkup, Davis noticed that Parmer did not have a reaction to her skin prick test. Davis tried it again: nothing.
Parmer was in fifth grade when she underwent an oral food challenge, a test in which a patient is given increasing amounts of the offending food and monitored to see if an allergic reaction occurs. A medical professional stands by with oxygen, epinephrine, albuterol and antihistamines in case it does.
Parmer said the quantity was tiny at first—mere milligrams—and she gradually worked up to nearly a spoonful of peanut butter and tahini paste during the test. Still, no reaction; she had outgrown her allergy, and her life became easier in an instant.
Parmer’s experience is not uncommon. A recent study in the Annals of Allergy, Asthma & Immunology journal examined reaction rates of mostly low-risk adults and children who underwent food challenges in five different allergy and immunology centers across the country. The individuals were identified as low-risk because of several factors, including the lack of a recent reaction and a history of tolerance to ingestion. The revelatory study found that 84 percent of the approximately 6,300 participants passed their oral food challenges without having any reaction, 14 percent had a mild to moderate reaction, and 2 percent experienced severe anaphylaxis, underscoring the importance of performing the test under medical supervision.
Davis, who is also an associate professor of pediatrics in the section of immunology, allergy and rheumatology at Baylor College of Medicine, was the lead author of the study. She explained that individuals undergo oral food challenges for multiple reasons.
“They either had a food allergy and wanted to know if they’d outgrown the allergy, or they’d had other testing that suggested a food allergy even though they had never ingested the food, or they had a history of a mild reaction but had never been found to be positive through tests,” Davis said.
Food allergies are caused by an abnormal reaction of the immune system to a certain food. They are different than food intolerances, such as lactose intolerance and celiac disease, because they trigger an overproduction of an antibody called immunoglobulin E (IgE). Physical symptoms of this reaction range from a minor tingling sensation around the mouth to life-threatening anaphylaxis—the higher the levels of IgE, the more likely a life-threatening allergy. Interestingly, a decrease in IgE levels as determined by blood tests over a period of time indicates the likelihood of outgrowing a food allergy.
The oral food challenge is considered the gold standard for determining the presence of a food allergy because the other two tests in the field—the skin prick test and the blood test—only measure sensitization to the food; neither reliably measures severity of a reaction or definitive presence of an allergy.
The skin prick test looks for the presence of IgE antibodies by piercing the skin and placing a drop of solution containing specific food allergens on a broad area of the body, often the arm or the back. In a patient with a history of a reaction to the food, if a hive appears, an allergy is likely present. The blood test also measures the presence of specific IgE antibodies, but both tests carry with them a high rate of false positives—meaning there can be a presence of IgE antibodies even if an individual has never had a reaction to that food.
Although the oral food challenge is the best means of determining a food allergy, allergists might choose not to perform this type of test because of the high risk of an allergic reaction, the burden of time, concern about cost to the patient and personnel constraints, according to the study co-authored by Davis. One goal of the study was to provide an accurate determination of the real risk of oral food challenges in non-research settings in order to help allergists in clinical practices around the country make everyday decisions about treating their patients.
More than 90 percent of all food allergies are caused by just eight types of foods. Four of those—milk, eggs, soy and wheat allergies—are commonly outgrown, whereas allergies to peanuts, tree nuts, fish and shellfish are often lifelong. Davis said that only about 20 percent of children with a peanut allergy will outgrow it, a statistic made more sobering by the fact that food allergies are on the rise in the U.S. and other developed countries. In fact, research compiled from the Centers for Disease Control and Prevention shows that food allergies in children increased approximately 50 percent between 1997 and 2011.
But it remains unclear as to why there has been a surge in food allergy cases, and why food allergies are all but nonexistent in underdeveloped countries. Theories range from genetic to environmental, and one proposition, the hygiene hypothesis, blames Western culture’s obsession with cleanliness.
“Our immune system has been geared to fight off things like parasitic diseases, and in first-world developed countries, we’re not exposed to these anymore,” Davis explained. “We think the immune system has been redirected to attack food.”
Perhaps that idling of the immune system explains why research related to the microbiome—described by science writer Carl Zimmer as the approximately 100 trillion bacteria and other microbes living inside the human body—is beginning to give clues about food allergies.
It is known that the microbiome plays a critical role in the immune system, and research has shown that the composition of the microbiome is related to the susceptibility of food allergies. In fact, studies using mice models have shown a class of bacteria called Clostridia protected mice against certain food sensitizations, which could potentially lead to future development of probiotic therapies.
Researchers and clinicians are optimistic that treatments for food allergies will be developed, but until then, the only course of action is avoidance of the specific food group. Still, there are the lucky ones who, for reasons not completely understood, experience a drop in their IgE antibodies. Some of them will sit at a doctor’s office and take a series of smaller bites, then larger ones. Then, like Parmer, they’ll celebrate with something long forbidden.
“The first thing I had was a Reese’s Peanut Butter Cup,” Parmer said. “It was really good.”