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The Gut-Skin Axis in Atopic Dermatitis

Patients with atopic dermatitis often ask what food has to do with their skin—but does diet play a role in eczema severity? Peter Lio, MD, FAAD, highlights what is known about the gut-skin axis and what evidence is available regarding food, probiotics, and eczema. Dr Lio is clinical assistant professor of dermatology and pediatrics at Feinberg School of Medicine at Northwestern University in Chicago, IL. He is a member of the Clinical Advisory Committee of the National Eczema Association.


Dr Lio: The skin in the gut have so much in common. I do think there is a fair amount of crosstalk. We talk about this larger system, the neuro‑immune‑cutaneous‑endocrine or NICE system. We know that all these guys are playing off each other. The nervous system is connecting our skin and gut and sending different signals. It's modulating aspects, blood vessels, and also directly inflammation, sensations of itch, sensations of heat, fullness. All of these things are happening. We can see on a number of levels, we're having these crosstalk nerves, the immune system, the endocrine system; all of them are working together. What's remarkable is that we see reflections across systems. When one system is hurting, we often see that reflected at another system as well.

We're lucky in dermatology, because our organ system is on the outside. We can see it, we can interact with it very, very easily, but there is no doubt, many patients feel, and I think many diseases require us to do more than just treat the skin. Sometimes something local is great. We can put something right on there, but for more serious things, it's like you can't cover your whole body with something and you often will need to do something internal to also get that internal inflammation or imbalance.

We are learning also that some of our ideas about how these atopic diseases are connected, may be flawed. I would argue for many, many years we felt that food allergies were driving atopic dermatitis. This is a common thing. To this day many people say, "What food am I eating that's making my skin this way?" Sometimes that is true, that can be a real thing and is an important thing to consider, but what we've learned is that the skin seems to be a portal for developing allergies, in particular food allergies. We've seen this play out with peanut allergy.

The idea is that when the skin barrier is broken and damaged, allergens in the air, food allergens and other allergens, can get into the skin and enter in this abnormal way and then create an allergy to that, so an abnormal immune response. That's pretty incredible. It suggests that when you eat the foods going through the gut in the normal way, that is a way to tolerize. Ideally, instead of saying, "Wait, don't eat peanuts till you're older," now we've learned just go the exact opposite. It's what we used to say to people, “maybe it's our allergic, wait till you're older." That's the worst advice—that's how you create an allergy. Instead, it's eat it early, eat it often. This way, your body will become tolerant to it and get the skin healed. Don't get it near your skin because we think you can transcutaneously sensitize to those allergens. That may be a central pathway. Atopic dermatitis seems to be the first in many cases, and it would be an amazing unifying theory. It's not proven yet, of course, but we think that there may be at least some patients where the skin barrier damage is the primary problem, and all of the other issues come from that. The allergies develop because of the skin barrier problem. If we could use moisturizers or something to cool it down in the beginning, it is very compelling that we could potentially block other allergies and stop the allergic march.

The most common question I’m asked—it dwarfs everything else—is the relationship between food and eczema. It's super important, it really is. The problem with it is that it's nuanced. First of all, absolutely, there is a connection. There are many connections, and deep important ones.

The first and most important connection is that we know the more severe your atopic dermatitis, the more likely you are to have actual food allergies of the IgE type, meaning you eat a peanut, you blow up, you get angioedema, anaphylaxis, potentially life‑threatening allergies. That's part one. In a huge portion of my patients, I'd say probably more than half of my severe atopic dermatitis kids and more than a third of my atopic dermatitis adults who are severe, have serious food allergies that they have to be careful about. They're not cheating. They're not sneaking a peanut. They're not sneaking eggs if they're allergic, because they will die potentially. They will need an epinephrine injection and hospitalization. We know they're not cheating. That's the first big one.

The second one is a little more complicated. Are there people that when they eat certain foods, they flare right up? Yes. There is a thing that's eczematous food reaction, have an eczema flare‑up from food. It ends up being pretty rare. The vast majority of patients who even do have that often have other symptoms like diarrhea, bloating, belly pain. It's like the food is causing a secondary reaction in them. It's rarer than I think is acknowledged. Many people are still looking for that food or foods.

There's another group of foods that's fascinating. This is the less specific inflammatory foods. They're not really allergic. It's not a specific thing. They clean up their eating, eat a little better, they do do better. There is something to be said for that too.

We can see it's a long discussion. Part of the problem is sometimes, families are disappointed because I didn't start with food. The truth is, I say, it's like Sutton's law: why do you rob banks because that's where the money is? Well, why don't you talk about food? Because that's not really where the money is, at least for my patients. By the time they've got to me, everybody's told them, "Cut gluten. Cut dairy. Do this. Do that." They've tried it already. If I spend time on that in the first visit, it's often very low yield at that point. That being said, it's non‑zero. It still can help. I usually save that for later on if they need it.

Is there a role for pre or probiotics, or maybe the combination, symbiotics?

I honestly think the answer is yes, but, A, it's still controversial. B, the effect, if it's there, is modest. C, I think it's a subtype issue. In other words, some patients are going to respond well to it, others really might not respond at all. That's why when you look at the studies, they are all over the place. It's so crazy. One big study shows yes, it definitely helps. So, that's why everyone argues.

The good thing is it does not seem to hurt. The risk of using a probiotic or prebiotic, or combo, symbiotic, is extremely low, as long as it's a reputable brand. There are some crazy case reports of weird stuff happening. It's not zero. Nothing is zero when we do an intervention, but it's really safe and generally very inexpensive, especially the ones I'm recommending. You can spend a fortune on them if you wish and get handcrafted artisanal probiotics that are delivered to you in a cooler or something, but I don't recommend those. Typically, I don't think you need to go that far. We do see some patients who respond.

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