Parents who have one child with peanut allergy may be shielding their other kids from peanuts when it’s not necessary, and might actually increase the child's allergy risk, according to a new study.

Canadian researchers found that a large percentage of siblings of kids with documented peanut allergy had never been exposed to peanuts, and had even been diagnosed as allergic without ever showing signs of it.

“Almost half of this group had never actually shown an allergic reaction to peanut,” said Dr. Elana Lavine, a pediatrician at Humber River Regional Hospital in Toronto, who led the study.

“Instead, they had been diagnosed with (peanut allergy) PNA by the use of allergy tests, such as skin testing or blood testing, and it is known that these tests are not perfect and may over-diagnose PNA in some cases,” Lavine told Reuters in an email.

She and her colleagues used the Canadian Peanut Allergy Registry to find information on 922 siblings of children with a peanut allergy. Parents completed a questionnaire about their children’s exposure and reactions to peanut, any allergy testing and whether the children had been diagnosed with PNA.

Results showed that 9 percent of the siblings of PNA children were reported to be peanut allergic. The researchers note that this is a much higher percentage than is seen in the general population, where 1 percent to 2 percent of children are peanut allergic.

While it’s true that peanut allergy can run in families, the study team writes in Clinical and Experimental Allergy, and genes may account for some of the higher allergy rates seen among siblings, misdiagnosis may also be contributing to inflated numbers.

Nearly 14 percent of siblings of PNA children had never been exposed to peanut. This was more likely when the unexposed child was born after an older child was diagnosed with PNA.

Current evidence indicates that being introduced to a substance later in life raises the risk of an allergic response, the researchers point out. So avoiding peanuts may be contributing to higher rates of allergic reaction when the siblings finally do encounter peanut.

“If a younger sibling of a PNA child isn't fed peanut until a somewhat older age, we may be inadvertently increasing that sibling's chance of becoming PNA too,” Lavine said.

It’s also possible that doctors or parents are just assuming the sibling is allergic or diagnosing them purely by skin testing, despite the child never having had an allergic reaction to peanut, she and her colleagues write in their report.

Katie Allen, a professor who studies peanut allergy at the Murdoch Children’s Research Institute in Melbourne, Australia, agrees that avoiding foods can be a problem. She warns, however, that there is still disagreement over whether avoidance actually increases the risk of developing allergy.

“I think the issue is that at the moment, the data is out as to how much allergen avoidance is the cause of food allergy,” Allen told Reuters in an email.

Allen noted that parents were advised in the past to wait up to three years before introducing foods like peanuts and eggs into their children’s diets. The American Academy of Pediatrics also told mothers to avoid these foods during breastfeeding and even pregnancy.

“And then about 5 or 6 years ago, these recommendations were reversed to say, well maybe that’s causing the problem,” Allen said.

Allen sympathizes with parents who are reluctant to expose their children to allergens for fear of a reaction. But, she said, performing a skin-prick test before ever exposing the child can cause more fear and confusion if the results are not conclusive.

She proposes that parents gradually introduce allergens into the child’s diet, starting with very small portions. “one eighth-teaspoon the first day, and then one quarter-teaspoon and then one half-teaspoon and then one teaspoon - slowly increasing the new food, then that’s likely to be safe, and if they have a reaction, it is more likely to be mild.”

If children have a reaction, they should then see an allergy doctor and get a confirmatory test, according to Allen.

Lavine and her colleagues write that a doctor-supervised challenge test with the actual food is also a safe way to find out if a sibling has the allergy.

Lavine said the education of both parents and physicians is important, especially in light of the recent changes to allergy policy.

“Families should be encouraged to speak with their physicians when making decisions about delaying particular foods for their children, and physicians should be aware of the changing literature on this topic,” she said.