PHILADELPHIA — The younger siblings of children who ate peanuts were more likely to develop peanut allergy, but that probability dropped substantially if the younger sibling was also introduced early to peanut, according to a poster abstract presented at the American Academy of Allergy, Asthma & Immunology (AAAAI) 2026 Annual Meeting in Philadelphia. 

The likelihood of peanut sensitization increased with the duration of eczema in the younger sibling, found Michelle F. Huffaker, MD, a clinical assistant professor of medicine and allergist/immunologist at Stanford Medicine in Emeryville, California, and her colleagues. The findings appear to align with the Lack dual-allergen exposure hypothesis, which posits that food sensitization occurs with environmental exposure, possibly through an inflamed skin barrier such as that resulting from eczema, but that early oral exposure can build tolerance to the allergen. 

“In my opinion, for the [potential] allergens that are important in your household’s diet, you should be feeding them early and often to your baby,” Huffaker told Medscape Medical News. In this study, early introduction to peanut mitigated the risk of younger siblings developing peanut sensitization, a finding that may be true for other food allergens as well, though evidence does not yet exist to show the same effect with other allergens, Huffaker said.

The researchers analyzed data on the younger siblings of participants in the LEAP trial, including their level of household exposure to peanuts, their incidence of eczema, and their sensitization to peanut. The LEAP trial involved 640 infants who were at high risk of developing peanut allergy, with half being given age-appropriate peanut foods several times a week starting when they were 4-10 months old and the other half avoiding peanut foods. Because half the households had more peanut exposure than the other half, it created an opportunity for an unintentional randomized trial for the participants siblings as well. 

There were 154 younger siblings of LEAP participants who received early introduction to peanut, resulting in higher cutaneous exposure for those siblings, and 143 younger siblings of LEAP participants who avoided peanut, resulting in those siblings’ lower cutaneous exposure to peanut. Within each of those groups, some families chose to feed peanut products to the younger siblings and others did not. 

Among the siblings of peanut consumers, 71 younger siblings were introduced to peanut in their first year of life and 83 were not. Among the siblings of peanut avoiders, 25 siblings consumed peanuts in their first year of life while 118 did not. 

The presence and duration of eczema in younger siblings were associated with the likelihood of peanut sensitization — the longer they had eczema, the more likely it was that they became sensitized to peanut (P < .001) — but those with early introduction to peanut had a lower probability of developing peanut sensitization (P = .019). Among siblings with no eczema, for example, 14% of those who did not consume peanut developed sensitivity to peanut compared with 4% of those who did consume peanut.

Among siblings who had eczema for 5 years, 27% who did not consume peanut and 9% who did went on to develop peanut sensitization. And in those who had eczema for 10 years, peanut sensitization occurred in 46% of siblings who did not consume peanut and 19% of those who did.

The researchers also looked at the odds of a younger sibling developing peanut sensitization based on who else was consuming peanut products in the house. A younger sibling’s odds of peanut sensitization were nearly 12 times higher if their LEAP participant sibling consumed peanut (odds ratio [OR], 11.71, P = .015) but nearly 17 times higher if the LEAP participant in the house and other older siblings ate peanut (OR, 16.74, P = .0085). 

Based on the LEAP trial findings, early introduction to peanut should involve at least 6 g of peanut products per week for the first 5 years of a child’s life if they have eczema, Huffaker said, but she added that “everybody really should be introducing [peanut] early” to help prevent development of peanut allergy. 

Given that atopy runs in families, “it’s not surprising that siblings of patients that we see for food allergy may have an increased risk of an atopic disease, such as eczema or food allergies,” Lucia You, MD, an allergy and immunology fellow at Vanderbilt University in Nashville, Tennessee, told Medscape Medical News after reviewing this study’s findings. “But I don’t think we’re quite as aggressive about targeting those patients and explicitly stating that younger siblings should be screened” for allergy or sensitization, she said. 

“What this study implies is that, if a younger sibling of a patient does have eczema, it might be worthwhile having the parent make a separate patient visit for the younger child to be assessed early, before they may have a first reaction,” she said. You also agreed with Huffaker that early and frequent introduction to potential food allergens may help mitigate the risk of developing sensitization to those allergens. 

The research was funded by the National Institute of Allergy and Infectious Diseases. Huffaker reported unrelated consulting for Takeda. You has no disclosures. 

Tara Haelle is a science/health journalist based in Dallas.