When LaNeatra Hammond’s daughter Lianna was 4 months old, she ended up in the emergency room with rashes and vomiting. An allergist determined she was allergic to milk, corn and soy. By the time she was 2 years old, she had avoided those foods but a skin test showed she was still allergic to milk. But the test indicated she was not allergic to corn and soy anymore.
“By age 4, she didn’t test positive for milk either. She does not have any food restrictions anymore,” says Hammond. “We’re relieved, but the idea of outgrowing allergies is a little confusing.”
In nearly every classroom today, there’s one or two children with a diagnosis of food allergies (1 in 12 nationally, according to a 2011 study published in “Pediatrics.”) Many of them were diagnosed as babies or toddlers. But more than a quarter of them probably aren’t allergic anymore.
Why does outgrowing happen?
Dr. Robert Wood, director of pediatric allergy and immunology at Johns Hopkins University School of Medicine, says that the answer will vary a lot depending on the age of the child and the specific foods involved.
“We think of it as their immune system gradually forgetting that it ever cared about that food. Why some do and some don’t, and why some foods are far less likely to be outgrown than others, is still not known,” says Wood.
The allergen makes a difference
Consistent evidence shows allergies to certain foods that are more likely to be outgrown. With 90 percent of food allergies being to “The Big Eight”: milk, eggs, tree nuts, peanuts, fish, shellfish, wheat and soy, research has determined that they aren’t all equally likely to remain allergies over a lifetime.
Dr. Brian Vickery, an allergist-immunologist and assistant professor of pediatrics at University of North Carolina-Chapel Hill, researches allergies and how they manifest in children.
“Most are the same foods over and over. When you look at that—differences in natural history are significant. Milk, wheat or soy— most will outgrow,” says Vickery.
Another factor that may affect outgrowing allergies is if they are multiple or single allergies, with multiple ones being more challenging to completely outgrow.
What’s happening inside a child’s body?
Vickery says that the outgrowing is not literal—it’s not the dilution of the allergy in the child’s body because they are getting bigger.
“It does not appear to be proportional to the size of the child. We used to think milk and egg were outgrown early in life—and gone by grade school. Some studies suggested that previously, but now, we see them well into the late teenage years. It can happen any time, to any sized child.”
Vickery says that outgrowing allergies is a key scientific question—it might help find a cure or treatment.
“We don’t understand mechanistically why it happens, but we observe it happening all the time. This is tolerance of the allergen, which is what we hope for when we develop treatments,” he says. “Part of our inability to come up with a cure is that we don’t understand what happens in nature when it cures it.”
It appears now that the outgrowing is really the rapidly changing immune system, which is less reactive to the allergens it once reacted strongly to.
To test or not to test: How accurate is the testing?
“Food allergy testing by both blood and skin tests are extremely inaccurate. While negative tests are usually correct, positive tests indicate a true food allergy less than half of the time. All tests therefore need to be interpreted very carefully,” says Wood.
Dr. Geoffrey Bacon, an allergist from Hampton Roads ENT-Allergy, says that testing doesn’t always eliminate confusion.
“A clinical history from parents is so important, along with a journal of symptoms. There are false negatives on the RAST test so we might miss something and the skin test has a higher false positive rate, says Bacon. “Symptoms are most important. We are treating a patient, not a test.”
While it is common to redo testing every few years, the food challenge is the true test.
“A swallow test is the most accurate. Then we know what food they were exposed to and can observe the symptoms and confirm they are characteristic of an allergic reaction,” says Vickery.
There’s evidence that the levels of an antibody called IgE are correlated to outgrowing allergies, and testing those levels to see if they’ve decreased may indicate less of an allergy.
Unfortunately, when it comes to allergies and outgrowing them, allergists and researchers are still playing detective to find out what happens and why.