While your older brother’s oversized Christmas sweater will undoubtedly be passed down to you, it appears that his peanut allergy probably won’t, according to preliminary research presented this week at the American College of Allergy, Asthma and Immunology (ACAAI) Annual Scientific Meeting.

The study, presented by ACAAI member and lead author Dr. Ruchi Gupta, analyzed the rates of food allergy among people whose sibling had been previously diagnosed with one and found that less than one in six carried their own version, though slightly more than half did have some degree of food sensitivity.

"Too often, it's assumed that if one child in a family has a food allergy, the other kids need to be tested for food allergies," explained Gupta in a statement. "But testing for food allergies if a reaction hasn't taken place can provide false-positives, as we saw in our research. More than half the kids in the study had a sensitivity to a food, but they weren't truly allergic. Kids who have a food sensitivity shouldn't be labeled as having a food allergy."

No Hand-Me-Downs Here

Gupta and her colleagues pored over the records of 1,120 people (ages 0 to 21) who had participated in the Chicago Family Cohort Food Allergy Study, ultimately looking at the 642 siblings of 478 index children (people with a documented food allergy). Only 13.6 percent of the siblings tested positive on the various allergy tests they were given (blood and skin prick) and had a documented allergic response to a food within two hours of ingestion, while 53 percent had a positive test but no allergic response. These responses could involve skin hives, shortness of breath, and vomiting, among others.

As for your legume-hating brother? Only 4.9 percent of people whose sibling had a peanut allergy were also diagnosed with one.

The foods tested for included peanut, eggs, and milk, with milk being the most common allergy at 5.9 percent. On the other side, wheat ended up being the food that most siblings were sensitive to at 36.5 percent. After looking at various other factors (family history, pet ownership), the only variables that were associated with developing food allergy was a previous history of asthma and eczema.

For that reason, Gupta’s team believes that it might be smart to offer allergy testing to these groups of people (oral food challenges specifically). Otherwise, they believe that allergists should stick to the current guidelines espoused by the National Institute of Allergy and Infectious Diseases (NIAID), which do not recommend routine screenings for the siblings of food allergic people.

"The risk of food allergy in one sibling, based on the presence of food allergy in another, has never been completely clear," said allergist and co-author Dr. Matthew Greenhawt. "This perceived risk is a common reason to seek 'screening' before introducing a high-risk allergen to siblings. But screening a child before introducing a high-risk allergen isn't recommended. Food allergy tests perform poorly in terms of being able to predict future risk in someone who has never eaten the food before. Our study showed that testing should be limited in order to help confirm a diagnosis, rather than as a sole predictor to make a diagnosis."

They do however believe that more extensive research will need to be conducted in order to determine the exact influence that siblings have on one another’s risk of food allergy.

Source: Gupta R, Walkner M, Lau C, et al. Food Allergy Sensitization and Presentation in Siblings of Food Allergic Children. ACAAI Annual Meeting 2015. 2015.

A previous version of this story incorrectly referred to Dr. Ruchi Gupta as a man when in fact Dr. Gupta is a woman.