Parents whose kids are allergic to peanuts may be relieved to know that it's possible their children could outgrow their allergy over time.

In a study of 80 children ages 4 to 14 with well-documented peanut allergies, researchers at Johns Hopkins Children's Center and Arkansas Children's Hospital found that some children completely lost their potentially serious or life threatening allergy to peanuts and that among those who did, there was a low risk of allergy recurrence. The findings are published in the July issue of the Journal of Allergy and Clinical Immunology.

"Although we once thought peanut allergy was a lifelong problem, we now believe certain children, namely those with low levels of allergy antibodies, may outgrow it," said senior author Robert Wood, a pediatric allergist and immunologist at Johns Hopkins. "Because of these findings, and the tremendous burden peanut allergies can cause for children and their families, I recommend that children with peanut allergy be retested on a regular basis, every one or two years."

The researchers found that children were more likely to outgrow their peanut allergy if they had low levels (less than 5 kilounits per liter) of peanut-specific IgE, the antibodies produced by the immune system that cause allergic reactions. These antibodies can be measured with a blood test that is widely available. Although a high level (more than five to 10 kilounits) of peanut IgE is typically associated with a clinical allergic reaction, it is not possible to predict the severity of the reaction simply based on IgE levels alone.

The 80 children in the study, all of whom had IgE levels of five or less, underwent an oral peanut challenge, a common allergy diagnostic tool in which subjects are fed peanut products in a safe clinical setting and watched carefully for symptoms, such as hives, coughing, difficulty breathing or vomiting. Wood noted that such food challenges, whose findings are valuable, should be done only under a physician's supervision.

More than half the children -- including those who had "failed" a previous peanut challenge and those with a history of severe, life-threatening reactions -- tolerated the challenge and were therefore considered to have outgrown the condition.

Researchers also followed up with 64 children who had "passed" peanut challenges in both this and a previous Johns Hopkins study to determine current peanut-eating habits and the possibility of allergy recurrence. Since their challenge, almost all the children had eaten peanuts, mostly infrequently and in small amounts. Two had suspicious reactions to peanut ingestion, meaning their allergy may have returned.

"Although recurrence of peanut allergy appears to be uncommon, we believe the risk of recurrence may be higher among those who do not consume enough peanuts to maintain their tolerance level. However, further study is needed to determine whether this is true, and whether 'outgrowers' should be encouraged to eat a certain amount of peanut," Wood said. Parents should always seek medical evaluation and guidance before giving peanuts to a child who may have outgrown the allergy, he added.

Experts say peanut allergies, which affect approximately 1 percent to 2 percent of young children and 1.5 million Americans overall, are on the rise. The allergy can be triggered by as little as 1/1,000th of a peanut and is the leading cause of anaphylaxis, the life-threatening allergic reaction that can constrict airways in the lungs, severely lowers blood pressure and causes swelling of the tongue or throat and sometimes death.

Co-authors of the study were David Fleischer and Mary Kay Conover-Walker of the Johns Hopkins Children's Center Division of Immunology and Allergy, and Lynn Christie and A. Wesley Burks of Arkansas Children's Hospital.

The study was funded by the National Institutes of Health, National Institute of Allergy and Infectious Diseases, the Eudowood Foundation for the Consumptives of Maryland and the Myra Reinhard Family Foundation.