Nearly four out of every 100 children in the U.S. have a food allergy, according to CDC data from 2007. Avoiding common food allergens, such as peanuts, eggs, tree nuts and fish, for the first few years of life was the prescription for prevention for many years, but in 2008 the American Academy of Pediatrics reversed these guidelines, noting little evidence existed to say the avoidance was preventing food allergies. Newer expert recommendations have even suggested introducing these foods early could play a role in preventing allergies. An idea known as the “dual-allergen exposure hypothesis,” which has to do with when and how children are exposed to allergens, could be a reason why.

Last month, I had the chance to listen to allergy expert Gideon Lack speak on the hypothesis at an allergy panel discussion during the Association of Health Care Journalists (AHCJ) annual conference.

The dual-allergen exposure hypothesis is the theory that exposure to food allergens through the skin can lead to allergy, while consumption of these foods at an early age may actually result in tolerance, as Lack explains in a 2012 article. Depending on the balance of these exposures, either tolerance or allergy will “win.” Children with eczema, for example, have a disrupted skin barrier that could allow exposure to food proteins in the environment – such as peanut oil in creams or peanut residue on tables. Under the hypothesis, if these children avoid peanuts but are still exposed to them in the environment, they might be more likely to develop peanut allergy.

Lack told the audience about two studies that could shed some light on researchers’ understanding of the hypothesis and the development of food allergy. One study is the LEAP Study, which involves a group of children assigned to avoid peanut-based foods until three years old and another group assigned to eat a peanut snack three times a week. The other is the EAT study, which is comparing breast-feeding plus feeding of allergenic foods with breast-feeding alone. However, Lack noted that very few evidence-based recommendations currently exist about when children should start eating allergenic foods, as health reporter Sandra Jordan explains in her blog on the AHCJ panel. With the prevalence of food allergy today, it will be interesting (and useful) to see where the future evidence from these studies falls.