July 11, 2024 – When it comes to atopic dermatitis – the most common form of eczema affecting millions of U.S. children and adults – are you what you eat?
It may come down to who you ask. Though studies have shown a clear link between dermatitis and food allergies, controversy abounds over which comes first – atopic dermatitis or the food allergy. And it is still unknown how often dermatitis results from a true food allergy (such as a milk, egg, or peanut allergy) or is the result of itching and scratching in response to allergy symptoms.
“Food-triggered eczema is actually really rare,” said Peter A. Lio MD, founding director of the Chicago Integrative Eczema Center. “The confusing part is that a lot of patients with AD have true food allergy … but the reaction is not an eczema flare-up, it’s hives, and they might experience anaphylaxis and swelling,” he said.
“We think that what is going on for a lot of patients is that the eczema leads to barrier damage in their skin,” he said, meaning, “this allows them to become allergic to all different things in the environment.”
About Atopic Dermatitis
Atopic dermatitis commonly begins in childhood, affecting as many as 9.6 million U.S. children under the age of 18. Some children outgrow it, while for others, it continues into adulthood. It can also begin in adulthood; currently, an estimated 16.5 million adults in the U.S. have been diagnosed with atopic dermatitis.
It is believed atopic dermatitis develops when the immune system becomes disordered and overactive. Research also shows that people with AD have physical and chemical disruptions of their skin barrier. They also lack a protein (filaggrin) that helps the body maintain a healthy barrier on the top of the skin. Because the skin microbiome – colonies of microorganisms, immune cells, and skin cells – is also altered, moisture is allowed to escape and unhealthy allergens, bacteria, and other pathogens enter and wreak havoc.
The result? Inflammation, and itchy, dry skin that, with scratching, leads to redness, swelling, cracking, “weeping” clear fluid, bleeding, crusting, and scaling. With repeated scratching, the skin can become dry and discolored, and it eventually thickens and hardens.
Teasing Out the Triggers
Symptoms of food allergies and atopic dermatitis often overlap, making it difficult to figure out if the food allergy is triggering the outbreak or the skin and its protective barrier becomes “leaky,” allowing the entry of the allergens that launch an immune reaction.
Dairy and Eggs
“There is some contention that dairy and eggs are the two really big trigger foods for eczema, yet there is not a lot of research to back that up,” said Jennifer Fugo, a licensed dietitian nutritionist, certified nutrition specialist, and host of the Healthy Skin Show podcast. “I’ve had clients who couldn’t tolerate those foods for whatever reason, a lot of times it had to do with other issues. So, I question: Is it really a trigger food? Does the person have actual antibodies (called immunoglobulin-E or IgE) that cause an instant reaction after consuming a food culprit, one that could be life-threatening? Obviously, these foods should be identified and removed.”
Tree and Grass Pollens
Potential culprits also include wheat, soy, as well foods that are related to tree or grass pollen (uncooked fruits and raw vegetables). Pollen allergies tend to trigger symptoms in and around the mouth and throat and broadly include raw fruits, like apples, peaches, and cherries, and uncooked vegetables, like carrots, celery, and fennel.
Sodium Intake
Findings from a recent study in over 200,000 adults showed that eating high-sodium foods may also play a role.
“We used to think that the kidney did all of the saltwater processing in the body, but it turns out the skin plays a large role,” said study co-author Katrina Abuabara, MD, an associate professor of dermatology at the University of California, San Francisco. “Almost all of the exchangeable sodium in our body is stored in the skin … to prevent water loss. Almost all of these people have poor barrier function and increased water loss … which may trigger some of the inflammatory patterns we see in eczema.”
Though the study did not show cause and effect, the results suggested that a 1-gram increase (less than half a teaspoon) of sodium in the diet was linked to 11% higher odds of having an atopic dermatitis diagnosis and 11% higher odds for severe atopic dermatitis.
There are a number of reasons to decrease salt intake, especially when it comes to heart health.
“Part of the story might also be salt’s effect on the gut microbiome,” said Lio, who's also a clinical assistant professor of dermatology and pediatrics at Northwestern Feinberg School of Medicine in Chicago.
What’s more, one of the largest culprits may be fast food: Data from the International Study of Asthma and Allergies in Childhood suggests that eating fast foods increased the risk of atopic dermatitis by 20%, and severe atopic dermatitis by 70%, in adolescents.
Pollutants
“A very powerful story has been unfolding in the last couple of years about pollutants and toxins,” said Lio, pointing to the recent California and Canadian wildfires. “It turns out that there is a chemical in smoke called diisocyanate, and this chemical has been shown to damage the skin barrier and affect the microbiome. Adults exposed to the smoke had a huge increased rate of developing new-onset AD.”
Diisocyanate is also found in fuel and the exhaust from cars and trucks. “There’s a really important connection between urbanization and eczema,” said Lio. “So, kids who live in urban areas, particularly those who live near highways, have much higher rates of AD than people who don’t.”
Do Elimination Diets Work?
An elimination diet involves not eating foods believed to cause allergic reactions or atopic dermatitis – such as milk products, eggs, wheat, soy, peanuts/tree nuts, and fish or shellfish – and then reintroducing some of these foods at a later date. But these diets come with a “massive caveat,” said Kara Fitzgerald, an Institute for Functional Medicine certified practitioner and global lecturer based in Sandy Hook, CT.
She explained there’s evidence that “if you put people on a full elimination diet, you can actually cause the full loss of tolerance, i.e., an anaphylaxis response,” she said. “I still think elimination diets are important but with nutritionist and doctor supervision.”
Fitzgerald, who's also a a licensed naturopathic doctor, also recommends a micro exposure approach, where reintroduction of potential food culprits is reduced but small amounts of these foods are kept in the diet to avoid severe reactions.
An alternative is a whole-foods approach, a strategy embraced by all of the experts interviewed for this story.
“Changing diet can make a difference,” said Lio. “Junk foods, sugary foods, highly processed foods all seem to have [negative] effects on the whole body – including the skin – and can be pro-inflammatory in some individuals.”
Fugo recommended thinking about nutrient density and diversity. “Nutrient density is crucial; there are a lot of data showing that certain nutrient depletions are associated with AD. And we need diversity because the more diverse your diet is, the more diverse your gut microbiome is,” she said.
Fitzgerald said it’s important to also “think about nutrients that turn the volume down on inflammation and help balance the immune system.” They include vitamin D, vitamin A, probiotics, and eating a plant-rich diet. (Most plant foods such as artichoke hearts and chicory are prebiotics.)
The ultimate goal? Talk to your doctor or practitioner “about a plan that will get you under good control,” said Lio. “Some people are in a continuous flare, and they end up using treatments that are too strong or unsafe for long-term use.”
“We’re shifting our goal from thinking about what to do for a flare-up to building a whole plan for what to do when the skin is quiet – daily stuff to help strengthen the skin and microbiome – and then a rescue plan if things start going crazy,” he said.