TUESDAY, Nov. 9 (HealthDayNews) -- If your child outgrows a peanut allergy, he or she should have foods containing peanuts at least once a month to prevent the allergy from returning, a new study suggests.

According to the results of the research, eating something with peanuts at least that often will help maintain a tolerance to them. But even though the allergy has apparently disappeared if the amount of peanuts eaten is limited, children should carry epinephrine for a while just in case a reaction develops.

"We were surprised a few years ago to discover that some children who had lost their peanut allergy got it back," said lead researcher Dr. Robert A. Wood, a professor of pediatrics at Johns Hopkins University. "We were surprised because that is something we had not seen with other food allergies."

In their study, Wood and his team studied 68 children who had outgrown their allergy to peanuts. The purpose of the study was to find out how many of the children became allergic again.

They also wanted to identify the risk factors that caused the allergy to recur, and to find ways to treat children who had outgrown their allergic reaction to peanuts, according to their report in the November issue of the Journal of Allergy & Clinical Immunology.

Wood's group looked at repeat peanut-specific immunoglobin-E (IgE) levels, did food challenges with peanuts, and had the children answer questions about what they ate.

The researchers found there was about an 8 percent chance of having a recurrence of peanut allergy. The risk of recurrence was much higher among children who avoided eating peanuts after they had outgrown the allergy, Wood's group reported.

"It is much less likely to get the allergy back if you are eating peanut on a regular basis once you have been able to tolerate peanut," Wood said.

Wood said that peanut is not unique. It is likely the same thing happens with other food allergies, such as milk or eggs. "The big difference is that when someone outgrows their milk allergy, even if they are not a big milk drinker, they are getting milk protein in their diet on a daily basis," he said.

"It is more common for people who have had a peanut allergy to still avoid the food even though we have told them they can put it back into their diet," Wood added.

"We now recommend that our patients eat concentrated forms of peanut at least once a month after outgrowing their peanut allergy in an attempt to maintain peanut tolerance," Wood's team wrote.

"We also recommend that patients and families who eat peanut frequently continue to carry injectable epinephrine for at least one year after passing their challenge. If they eat peanut only infrequently or in limited amounts, then patients should have epinephrine available indefinitely at all times because of their increased risk of recurrent allergy," the researchers concluded.

Wood noted that all allergies are on the rise in developed countries, but are almost unheard of in developing countries. Part of this increase can be explained by the so-called hygiene theory, he said.

"The less an infant is exposed to germs and infections, the more their immune systems can focus on things like allergy," Wood said. "Allergies are much less common if you grow up on a farm, have close contact with animals; the more exposure you have to bacteria and other infections early in life, the less likely you are to have allergies," he added.

"While peanut allergy was often considered to be lifelong, studies from several centers have shown that about 20 percent of young children with the allergy are able to consume peanut at school age," said Dr. Scott H. Sicherer, an associate professor of pediatrics from the Jaffe Food Allergy Institute at Mount Sinai School of Medicine.

"This exciting discovery is tempered by the observation, reported by our group and several others, that some of the children eventually had a recurrence of the allergy," he added.

In Sicherer's practice, he monitors young children with peanut allergy to see if they outgrow it. "When we plan to have the child eat peanut under doctor supervision, we explain to families that we would have them truly add peanut to the diet if they successfully tolerate the food," he said.

In addition, when a child successfully ingests peanut, he has the family give peanut and has them no longer avoid the food. Not doing this seems to increase the risk that the allergy could recur. "We have them continue to have emergency medication available for a year or two until it is clear the child is eating peanut routinely. If the child refuses to eat peanut, we would need to test them periodically to know if a danger has re-emerged," Sicherer said.

More information

The National Institute of Allergy and Infectious Diseases has a primer on food allergies.