The increase in food allergies over the past several decades is real and multifactorial, and multiple environmental changes over this period have likely played a role. These include how new foods are introduced, epigenetic factors, skin barrier status, and alterations of the microbiome. The interaction of each of these environmental factors with genetics and other influences clearly contributes to the clinical manifestations of food allergies.

The prevalence of food allergies has increased over the past 30 to 40 years, although the numbers vary according to how we define food allergies and because many people believe that they have food allergies (as reported in patient questionnaires) when they actually do not. This may be the result of fairly high false-positive rates on IgE allergy testing that are not confirmed by a true diagnostic test, such as an oral food challenge. Nevertheless, there is clearly a dramatic rise in the prevalence of food allergies, and the environment must be playing a role in this since our genes do not change that quickly.

Several environmental changes have likely impacted the development of food allergies, one of which is how new foods are introduced into a patient’s diet. For example, 20 to 30 years ago, it was recommended not to eat certain foods too early, which clearly contributed to the food allergy rise. In addition, our environment has changed, which probably has affected epigenetics, or how our genes are expressed. This may be reflective of a combination of things, including an exposure to pesticides and stronger detergents, potentially breaking down the epithelial barriers of the skin and gastrointestinal tract. However, additional work is necessary to fully understand these environmental changes.

Over the past 40 years, changes in the microbiome to which we are exposed, also called the “hygiene hypothesis,” have been implicated in the food allergy rise. However, attempts to enrich our microbiomes through supplementation with Lactobacillus, for example, have had no consistent effect on food allergies. In addition, microbiomes are affected by not only what we eat but also when foods are introduced. Is the change in the microbiome causing food allergies, or are people avoiding certain foods and thus causing the microbiome to change? So, it is unclear which comes first, and the results of animal studies are difficult to interpret. Additional studies are needed because these changes in our microbiomes are likely multifactorial.

We do know that uncontrolled or severe eczema really increases the risk of food allergies. Therefore, when advising parents about the prevention of food allergies in their second child after their first child developed food allergies, the 2 things I look at first are early food introduction and the presence of eczema.

We know that the early introduction of peanuts, milk, eggs, and cashews can be preventive and is probably beneficial. If foods were introduced early and the patient does not have eczema, you can look at other risk factors. Vitamin D deficiency has been implicated in food allergies, but vitamin D supplementation has not worked, although exposure to sunlight may be important. Early exposure to antibiotics for frequent infections may have altered the microbiome and played a role. Finally, family history as a risk factor remains unclear. Although the risk of food allergies in identical twins is increased, these patients do not always share the same food allergies, so there is clearly both an environmental and a genetic effect.