Do Food And Environmental Allergies Cause Eczema? Not Necessarily


By Neal Jain, M.D.

Published On: Aug 8, 2017

Last Updated On: Jul 15, 2021

Allergies do play a role in eczema for many patients, but there are also many patients for whom allergies don’t play a role. For each patient, it’s important to figure out which allergies are involved, if any, and how to manage those allergies.

Allergic inflammation

Eczema has many factors. We know that there is skin barrier dysfunction and there is allergic inflammation, and these things can play off of each other.

Normal skin has a good barrier that keeps moisture in and helps to prevent allergens and irritants and whatnot from getting through the skin and stimulating the immune system. But in eczematous skin that barrier isn’t working well, so water is lost and allergens and irritants and infectious agents can penetrate the skin, causing allergic inflammation. In some cases foods might be moving from the inside out although I’d say that is less common than is diagnosed.

Allergic inflammation of the skin is sometimes caused by allergies but not always. An infection with bacteria can also play a role, as can emotions and habits. All of these things can lead to the cycle of itching and scratching and rash.

Ultimately, we need to break that cycle. But that’s not a simple process.

I like to equate eczema skin to a broken PC. Sometimes things just don’t work, but you can’t just hit the “escape” key, the “alt” key or “control” to reboot; you must hit all of these keys at once. Similarly, you have to do multiple things together to get the skin to work right. You have to manage the infection and bacterial toxin production, you have to get rid of the allergies if they exist, and you have to repair and restore the skin so that it functions as a barrier. You also have to figure out how to handle the emotional side of this.

Irritants and allergens

We know that Staphylococcus aureus is important on the skin, but we also know that staph produces proteins or toxins, and these toxins can stimulate the inflammatory response. They can actually drive the inflammatory process and lead to allergic sensitivity. I think that’s very important to understand. I also think that’s why bleach baths often help so much; they help to get rid of staph.

To break the itch/rash/scratch/rash cycle, we need to identify and eliminate potential aggravating factors such as irritants as well as allergens. And when an infection develops we try to get rid of it using bleach baths. Sometimes in severe patients we use antibiotics.

How do we identify and eliminate irritants and allergens from the skin of patients with eczema? This is really difficult, especially in kids who have bad eczema. And the reason that it’s hard is because our tests are very imperfect.

A lot of kids with eczema test positive to a lot of things, and when this happens, it’s hard to clarify what is really contributing to their eczema, especially if their eczema is not under control. There’s even some data that suggests that people make IgE against some of the proteins in their own skin — especially when their eczema is severe (IgE, immunoglobulin E, is a type of antibody important in fighting parasitic infections but is also important because it is produced when an individual is allergic to a food or airborne allergen; this antibody is responsible for starting allergic reactions).

Nonetheless, we do need to try to identify the food allergens, as well as the environmental allergens that are contributing.

Food allergies and eczema

What percentage of Americans believe they have food allergies? It’s been going up rapidly. A study done several years ago found that about 25 percent of people in this country believe they have food allergies, and I’ve got to think it’s 30 to 35 percent today. It has almost become a fad.

What percentage of Americans actually have food allergies? Somewhere between 2 and 5 percent of the population. A lot of people believe they have food allergies but they don’t.

Why is that? The media has sensationalized food allergies, and they’re an easy thing to blame. I also think that more and more people are looking for answers to many conditions that don’t already have answers, and they are getting tested for allergies. I see a lot of kids coming in with attention deficit disorder or autism, and their parents have a strong belief that they’re eating something that they’re allergic to that’s contributing to their condition.

Sometimes allergists are doing tests for foods in a situation where foods are unlikely to be causing the condition. More often a doctor, a primary care doctor, a naturopath or a chiropractor says, “Hey, let’s run a panel of food tests and see what comes up.” And this leads to a lot of people being told they have allergies.

Of course, we know that people with certain environmental allergies will test positive for certain food allergies even when they are not allergic to those foods. For example, in Wisconsin we see a lot of people test positive to shellfish even if they have never eaten shellfish. They’re really allergic to dust mites or cockroach, but some proteins are similar between cockroaches, dust mites, and shellfish, so they test positive to shellfish.

In Arizona, kids with environmental allergies often test positive for corn, wheat, soy, peanut, carrots, tomatoes, potatoes and rice. That’s because, believe it or not, in Arizona there is a lot of pollen in the air, and those foods have relatives in the pollen world.

Diagnosing food allergies

The gold standard for diagnosing a true food allergy is a food challenge. Unfortunately most people don’t go through this process. And if kids have bad eczema, you really have to get their eczema under control before you can reliably do a food challenge.

What is a food challenge? Essentially what you do is you eliminate a food from a patient’s diet, and then in a controlled setting — ideally in the office of an allergist who’s adept at doing this — you try to reintroduce the food in a graded fashion and you monitor the patient to see if they have any reaction to it.

It’s not difficult, it’s not rocket science, to diagnose food allergies — at least that’s my opinion. Food allergies are reliable, they’re reproducible, they’re consistent and they’re timely. If someone eats a specific food and seems to react to it just some of the time, then that person doesn’t have a food allergy.

Apart from the gold standard, the food challenge, other food allergy tests are out there. IgG tests are common but I don’t think they have any role to play in determining food allergies (IgG, also called gamma globulin or Immunoglobulin G, is important in signaling of the immune system and in fighting and preventing infections in the blood and in other parts of the body, including viral infections and most types of bacterial infections).

The body puts a number of processes in place whenever it’s exposed to things that are foreign, including foods. The body’s basic goal is to try to determine whether a foreign thing is harmful or not. If it determines something is not harmful, it has an active process to signal to the rest of the immune system not to react to that particular thing, and if it determines something is harmful, it puts another process in place.

An allergy develops when these two processes get mixed up. But IgG tests simply signal that your body is reacting to something. If we all went out and had IgG tests done, each and every single one of us would test positive to foods. Why is that? Well, we all eat, right? And if you eat, your body makes IgG antibodies to foods to signal to the rest of your body how to react to these foods.

There’s never been any scientific data to suggest that IgG tests correlate with allergies. I think that IgG tests are great only if you want to lose weight because you will be told to avoid all of the things that are in the Western diet.

Food allergies do exist and although in some the symptoms can be severe and even life threatening, in others the symptoms may be more mild and include worsening of eczema.

Oral allergy syndrome is a very real thing, and I would classify it as a real food allergy. If you get an itchy mouth or throat when you eat certain fruits or vegetables, that’s oral allergy syndrome.

Some people are allergic to certain pollens. What is pollen? It is nature’s way of reproducing itself; trees and grasses and weeds make pollen, and there are proteins in those pollens that we can be allergic to. That’s why we get itchy eyes, mouth, throat, and palate when we’re in pollen season.

Now, what are fruits and vegetables? They’re another of nature’s ways of reproducing itself, and it turns out that many of the proteins found in fruits and vegetables are similar to the proteins found in pollen. If you take a handful of fruit or a bite of it, and it’s related to a pollen that you’re allergic to, it can make your mouth itchy because your immune system has a hard time distinguishing between the two. That’s a real food allergy — and it’s a relatively common type of food allergy.

The point is that diagnosing food allergies can be difficult and identifying whether a food is truly causing a problem requires obtaining a good history; testing is used to help confirm the diagnosis but sometimes food challenges are necessary to be sure. This is especially true in patients with eczema who may test positive to a variety of foods.

Environmental allergens

I’ve practiced in Arizona for the last couple of years, and environmental allergens are hugely important for many of my patients with eczema. They repeatedly tell me that every time they go out and do something like play soccer, their legs break out like crazy, and they have to step up their skincare, taking baths and doing wet wraps and everything.

I think that that’s a clear-cut sign of an environmental allergy. It makes sense because they’re running around in grass and grass gets onto their skin, and if they’re allergic to grass, that drives the inflammatory process.

There’s also evidence that breathing something that you’re allergic to can drive a systemic immune response, making you itch. This has been best studied with dust mites, but you see it with animals, you see it with grass, you see it with other things.

What percentage of the US population will test positive to something on an environmental skin test? The answer is 50 percent — about 50 percent of the population test positive to at least one allergen. Not all of those people have disease; you can test positive without having environmental allergy symptoms or eczema or anything like that. But 50 percent of the population will test positive for something.

Testing for environmental allergies

What is the best method to determine if someone really has an environmental allergy? We’ve already talked a bit about this. There are skin tests and blood tests — more specifically, there are intradermal skin tests and patch skin tests, and there’s IgG blood testing — and the one that I think has no validity is the IgG testing.

Patch testing, which is sometimes called contact dermatitis testing, can be helpful for diagnosing whether people are allergic to certain chemicals or cosmetics but it probably doesn’t have a role in determining if food allergies are a causative factor in eczema.

Old school allergists used to do a lot of intradermal testing, injecting different things under the skin, and we’re re-ally trying to move away from that now because the data suggests that you get a lot of false positives (people who are not truly allergic may test positive).

It comes down to the percutaneous scratch test or IgE testing. For environmental allergies, if someone is off of antihistamines, the data seems to be a little bit better for skin tests than for IgE tests, but there is strong correlation between the two.

For foods, it depends on the situation, but if you get a negative test for food, that’s actually more conclusive than a positive test; negative tests are actually pretty darn good at ruling out food allergies but positive tests are not good at ruling in food allergies unless there’s a clear-cut history of someone reacting consistently to a food.

Food allergy example

If Johnny eats peanuts and breaks out in hives at one point, and then after avoiding peanuts for a year, he accidentally takes a bite of his brother’s sandwich, which has peanuts, and he once again gets hives and swells up, I don’t need the test to tell me that he’s allergic to peanuts. It’s consistent, it’s timely, and it’s reproducible.

I can do a scratch test, but it’s simply to confirm that he’s allergic. Now, if Billy comes in with a little bit of eczema on his arms and he tests positive to peanut, is he allergic to peanuts? That’s harder thing to interpret, especially if he’s never eaten peanuts before.

If his mom tells me he has eaten peanuts and nothing has happened, or if he eats peanut butter sandwiches every day, then no, he’s not allergic to peanuts. There’s a false positive. In the absence of a good history, positive tests are only accurate just 50 percent of the time — at best. That’s an important point to understand.

Environmental allergy example

Here’s another story. A while back two adult patients came in to see me and they both had bad feet dermatitis. We looked for causes, and they both had environmental allergies and allergies to animals, yet they both had carpeting and dogs.

Now, I have a dog and the amount of dog hair that we pull up every day when we vacuum is crazy. These patients tried using high potency topical steroids and doing all kind of things to get their feet dermatitis under control but while these things would help, the dermatitis persisted.

One of these adults finally got rid of their dog and one of them didn’t — and one of them got better and one of them didn’t. That helped me to understand that environmental allergies really can play a role in eczema. And at times, despite the best treatments and skincare, the eczema will persist until the environmental trigger is removed.


Does anyone know what’s in dust? There are about four things, right? Of course, the amount of each depends on where you are in the country or the world and on the circumstances in your home (such as animals in the home, carpeting, etc.). First of all, there’s human skin; we all shed at least a couple of pounds of skin in a year, and you might shed more if you have eczema or skin conditions. There are also dust mites. And there’s animal dander and bug parts.

Allergists have done some cool studies in different parts of the world to prove that dust is a universal problem. There’s an island off the coast of South Africa where there hasn’t been a cat for something like 20 years because they were exterminated in an effort to get rid of toxoplasmosis, which is a cat-borne disease. Some kids there have never seen a cat in their lives, yet they test positive to cats. Why? Because cat dander in dust is everywhere. You can be allergic to something even if you’ve never seen it.

Allergy shots

Can allergy shots be of help? The data on allergy shots and eczema is evolving. Five years ago, most allergists would probably say they may make things worse, not better. But the data now suggests that they do help with eczema in the long run for many people. It often takes time before they start to help; people often get worse before they get better. And it’s not universal. We don’t yet know the percentage of people with eczema that they might help.

In summary, while food and environmental allergies really can play a role in eczema, they don’t generally cause the condition. And diagnosing allergies, particularly food allergies, can be problematic. You need to take a multifaceted approach to eczema. It takes work to control this condition.

Excerpted from a presentation by Dr. Jain at the National Eczema Association’s annual patient conference.

Neil Jain, M.D.

Neal Jain, M.D., is a pediatric allergist with a special interest in atopic dermatitis and food allergy. He is in private practice in Gilbert, AZ, and also teaches pediatric residents at Maricopa Medical Center in Phoenix, Arizona.

Get the latest eczema news delivered to your inbox.