Scientists at the University of Alberta and University of Manitoba have discovered that the microbial environment in the gut of infants may play a role in the development of food allergies. They are gathering more data to see which bacteria, when present or not present, are more or less likely to increase the risk of food allergy development to common foods such as egg, peanuts, and dairy. What I would bet is that there is a big difference between breast-fed and non breast-fed infants, for starters. Secondly, exposure to antibiotics, particularly in the first 6 months of life, is known to have long-term effects on the microbiome of infants.
Reference:University of Alberta Faculty of Medicine & Dentistry. "Infant gut bacteria and food sensitization: Associations in the first year of life." ScienceDaily. ScienceDaily, 4 March 2015. www.sciencedaily.com/releases/2015/03/150304130915.htm.