Pediatricians used to tell parents to wait until children were toddlers before feeding them foods like peanuts and egg, common causes of food allergy. The theory was that early exposure to such allergens might be driving the development of food allergies, in which the immune system reacts to harmless food molecules as if they were dangerous. 

But that didn’t stop allergy rates in U.S. children from going up—by 50%, from 1997 to 2011. 

It turns out that giving children allergens early actually reduces the likelihood that they’ll develop an allergy. A landmark 2015 study found this to be true for peanuts. The U.S. National Institutes of Health released updated guidelines in 2017 encouraging early exposure, and scientists were able to show last year that this led to a drop in peanut-allergy diagnoses. Judging from the scale of the decrease, tens of thousands of diagnoses were averted.

A study published June 8 in JAMA Pediatrics finds that the same appears to be true of eggs. Researchers found that after new guidelines were adopted in Australia, urging parents to introduce eggs early, rates of egg allergy declined by 17%. That’s further proof that early exposure, far from causing food allergy, protects against it.

What do we know about preventing food allergies?

It’s not fully known why people develop food allergies, but scientists suspect that it has to do with how the body first encounters an allergen. “We know now that introduction of a food allergen to the gut, meaning the intestines, is going to teach the immune system that that food is safe,” says Dr. David Hill, a pediatric allergist and immunologist at Children’s Hospital of Philadelphia. By contrast, if the immune system first encounters an allergen in another way—through food particles from a parent’s meal getting on a child’s dry, broken skin, for instance—that will, for some children, “teach the immune system that that food allergen is dangerous.”  Scientists suspect this is why eczema, which involves cracked, inflamed skin, seems to be linked to developing food allergies.

 The message of early exposure seems to be reaching parents, says Dr. Jennifer Koplin, an epidemiologist at the University of Queensland in Australia and an author of the new study. In the latest research, “almost all infants were eating egg in the first year of life, and more than half had already introduced it by seven months of age,” she says.

How should you give young children eggs?

The egg should be cooked well and mixed into their usual foods, suggests Koplin. “The guidelines at the moment recommend giving out soon after you start solid foods, and we say that's generally around six months of age,” she says.