Food Allergies Are On the Rise—Is Skin Exposure to Blame?
As an allergist, the number one question I get from patients and friends is: "Why are food allergies on the rise?” I always get excited when asked this, because it is a topic we do not discuss enough nor have general awareness about. With food allergies more than doubling over the last couple of decades, we have an epidemic on our hands, but the reasons for this rise are not well known.
There are a few leading theories behind the rise in food allergies. One is the “hygiene hypothesis,” suggesting our children’s increasing lack of exposure to germs (including bacteria, viruses, and fungi) may increase their susceptibility to allergic diseases. Another is changes in our food system, such as the introduction of genetically modified organisms (GMOs) and chemicals in our foods. In short, the rise in allergies appears to be multifactorial. We are learning more and more about this complex process as time (and research!) goes on.
While we cannot say for certain why food allergies are on the rise, we can say we have better research around prevention. For example, we now know the timing of food introduction is key. If you wait to introduce allergens until 12 months of age, a child is FOUR TIMES more likely to develop a food allergy!
Research around prevention is relatively recent. When I was completing my residency in pediatrics back in the mid-2000s, the American Board of Pediatrics recommended parents wait until their child was three to introduce high-allergenicity foods like nuts and seafood. Since then, research has done a complete 180, and pediatricians now recommend the introduction of high-allergenicity foods as early as four to six months of age to help reduce the chance of developing food allergies. It is also important infants ingest these foods as early and consistently as possible to help “teach” the immune system that these foods are not dangerous intruders to the body.
There seems to be a critical window of time before a child starts eating solids, however, where there may be alternative exposures that impact the way a child’s immune system learns to deal with these allergenic foods. This is especially important for infants who are more susceptible to food allergies based on genetics or family history.
Epicutaneous sensitization: developing allergies through the skin
Ironically, and importantly, it turns out not all early exposure helps prevent food allergies. Recent research suggests early exposure to allergens through your skin could put you at a higher risk of developing food allergies! We are learning more about epicutaneous sensitization, which is the hypothesis that allergies can develop through skin exposure. There is evidence supporting the idea that an impaired skin barrier, as we see in kids with atopic dermatitis (eczema), may contribute to the development of food allergies through increased exposure to the allergen via the skin. This may be one of the reasons why children with eczema generally have a significantly higher risk of food allergies.
Interestingly, the human body responds differently to food ingested orally versus absorbed through the skin. Usually, allergenic protein exposure through the skin is minimal since only a small amount ends up absorbed into the bloodstream. While the details of the skin barrier involvement are still being explored, there has been an increased focus on interventions aimed at repairing the skin barrier as a way of preventing food allergies and other types of skin allergies.
Although we still have much to learn, our understanding of the rising epidemic of food allergies is improving. We have made significant strides in identifying ways to prevent food allergies in infanthood, but additional research is needed before the allergist community can more definitively respond to the “why the rise” question—because the short answer is: we still don’t know.
— Anjuli Mehrotra, MD
Anjuli Mehrotra, MD is a double board-certified physician in allergy/immunology and pediatrics. She is the CEO and Co-founder of Evme, and an Adjunct Clinical Instructor at Lucile Packard Hospitals and Clinics at Stanford, where she’s also been involved in food allergy research.