A landmark McMaster University study of 2.8 million children worldwide has identified key early-life factors that raise the risk of food allergies. The findings could help parents, clinicians and policymakers better target prevention.
Food allergies have surged in recent decades, leaving many parents wondering why some children react to common foods while others do not. A new global study from McMaster University offers some of the clearest answers yet, showing that a mix of early-life factors — not a single cause — drives the risk.
The research team analyzed data on 2.8 million children from around the world and found that about 5% develop a food allergy by age 6. The work, one of the largest and most comprehensive examinations of childhood food allergy to date, is published in the journal JAMA Pediatrics.
The team did not follow one group of children over time. Instead, they conducted a systematic review and meta-analysis, pooling results from 190 existing studies on childhood food allergy. Many of those studies used food challenge testing, in which a child eats a suspected allergen under medical supervision, considered the gold standard for confirming a true allergy.
By bringing together such a large body of evidence, the researchers were able to sort through more than 340 potential risk factors and identify which ones consistently mattered most.
One of the strongest signals involved eczema, a common inflammatory skin condition in infants. Babies who developed eczema in their first year of life were three to four times more likely to go on to have a food allergy. Early wheezing or nasal allergies also raised the odds.
Family history played a major role as well. Children with allergic parents or siblings were more likely to develop food allergies themselves, especially when both parents had allergies. That pattern underscores the importance of genetics, but the study also shows genes are only part of the story.
“Our study highlights that genetics alone cannot fully explain food allergy trends, pointing to interactions – or a ‘perfect storm’ – between genes, skin health, the microbiome, and environmental exposures,” senior author Derek Chu, an assistant professor in McMaster’s Departments of Medicine and Health Research Methods, Evidence and Impact, said in a news release.
The timing of introducing certain foods emerged as another key factor. Waiting too long to give babies allergenic foods such as peanuts, tree nuts and eggs increased the chance of developing an allergy. In particular, babies who tried peanuts for the first time after 12 months of age were more than twice as likely to become allergic to peanuts compared with those introduced earlier.
That finding aligns with a growing shift in pediatric guidance over the past decade, away from delaying allergenic foods and toward careful early introduction for many infants, especially those at higher risk. The new study strengthens the evidence base behind that change by drawing on data from millions of children.
Antibiotic use in early life also stood out. The analysis found that antibiotics given in the first month of life were linked to a higher risk of food allergy. Antibiotics taken later in infancy and during pregnancy were also associated with increased risk, but to a lesser degree.
Scientists suspect that antibiotics may disrupt the developing gut microbiome — the community of bacteria and other microbes that live in the digestive tract — at a critical time, influencing how the immune system learns to tolerate or react to foods. The new findings do not mean antibiotics should be avoided when they are clearly needed, but they add to calls for more careful, targeted use.
Importantly, the study also identified factors that did not appear to raise the risk of food allergies. Low birthweight, being born after the due date, partial breastfeeding, maternal diet and stress during pregnancy were not associated with higher food allergy risk in the pooled data.
That kind of information can be reassuring for families and can help focus prevention efforts where they are most likely to make a difference.
By clarifying which infants are most vulnerable — for example, those with early eczema, allergic parents and delayed exposure to allergenic foods — the findings could guide pediatricians and policymakers in designing targeted strategies. These might include earlier introduction of specific foods under medical guidance, closer monitoring of high-risk infants, and more judicious use of antibiotics in newborns.
The authors also see a roadmap for future research.
“This study has broadened our understanding of food allergies,” Chu added. “Future studies should measure and adjust for the same key factors, include more diverse populations, and use food challenge testing more often. New randomized clinical trials and updated guidelines are urgently needed to move our findings into action.”
Food allergies can affect every part of a child’s life, from school and social activities to mental health, and can be life-threatening in severe cases. While this study does not offer a simple fix, it provides a powerful evidence base for smarter prevention and better-informed care.
As new clinical trials and updated guidelines emerge, families and clinicians may soon have clearer, more personalized strategies to reduce the risk of food allergies — starting from the very first months of life.