It now appears that the solution to avoiding peanut allergies, ironically, is eating peanuts.

Every year, about 15 million Americans suffer from food allergies. For those with severe allergies, symptoms include generalized hives, itching, flushing, swollen lips and tongue, difficulty breathing, wheezing, fainting, vomiting, abdominal pain, low blood pressure, and a critical decrease in the flow of oxygen to the brain and other vital organs.

The foods that are most likely to cause these severe allergic symptoms are milk, eggs, peanuts, tree nuts, soy, wheat, fish, and shellfish. One of these eight foods, however, stands above the rest, affecting about 3 million Americans, and occasionally causing fatal or near-fatal allergic reactions. Peanuts. Every year between 75 and 100 people die from peanut allergies. Although children often outgrow allergies to milk or eggs by the time they go to school, peanut allergies are usually life-long.

Historically, recommendations on how to avoid peanut allergies were ineffective. Advisory groups in the United Kingdom in 1998 and the United States in 2000 proposed that children would be less likely to develop food allergies if they avoided allergenic foods when they were babies. These groups also recommended excluding allergenic foods from mothers during pregnancy and during breastfeeding. The problem with these recommendations was that they didn’t work. The incidence of food allergies remained unchanged. In 2008, confronted with overwhelming evidence that their recommendations had been useless, both of these advisory groups withdrew them.

A few years later, a rather surprising observation changed the approach to avoiding food allergies. Clinicians noted that peanut allergies were 10 times more prevalent in Jewish children in the United Kingdom than in children of similar ancestry in Israel. They also noted that whereas infants in the United Kingdom avoided peanut-based foods, infants in Israel ate a peanut-containing snack called Bamba, consuming about 7 grams of peanut proteins every month. Early introduction of peanuts, it appeared, might be lessening the risk of peanut allergies later in life.

Between 2006 and 2009, emboldened by this observation, researchers in the United Kingdom performed a formal study. Called the LEAP trial, which stood for Learning Early About Childhood Allergy, it included 640 children between 4 and 11 months of age. Because all of these children had severe eczema or egg allergies or both, all were considered to be at high risk for peanut allergies. Researchers separated these children into two groups. One group consumed at least 6 grams of peanut proteins every week divided into three meals. The other group avoided peanut proteins altogether. Researchers than followed these children until they were 5 years old, finding that 13.7 percent of the peanut-avoidance group and 1.9 percent of the peanut-consuming group were now allergic to peanuts—an 86 percent decrease!

After the LEAP trial was over, researchers wanted to find out what would happen if these peanut-consuming children stopped eating peanuts for one year. Would they still be resistant to peanut allergies? Or did they need to keep eating the peanut proteins to avoid the allergies? The answer was that resistance to peanut allergies persisted. Researchers found that 21.5 percent of the participants in the peanut-avoidance group and 2.4 percent in the peanut-consuming group were allergic to peanuts. Even after avoiding peanuts for a year, the tolerance to peanuts remained. Four years of eating peanuts appeared to be enough to induce a long-lived unresponsiveness. Subsequent studies will determine just how long this unresponsiveness lasts.

As a consequence of these studies, in 2017, an expert panel reporting to the National Institute of Allergy and Infectious Disease at the National Institutes of Health issued the following guidelines:

1. Parents of children with severe eczema, egg allergies or both should introduce peanut-containing foods as early as 4 to 6 months of age to reduce the risk of severe peanut allergy.

2. The total amount of peanut protein to be regularly consumed per week should be approximately 6 to 7 grams divided over three or more feedings.

3. For infants without eczema or any known food allergy, parents can give potentially allergenic foods early in life.

Although it might seem counterintuitive, the choice to withhold allergenic foods early in life appears to increase, not decrease, the risk of food allergies.

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Paul A. Offit, MD, is a professor of pediatrics and director of the Vaccine Education Center at the Children’s Hospital of Philadelphia. His most recent book is Pandora’s Lab: Seven Stories of Science Gone Wrong (National Geographic Press, April 2017).