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Ep. 10: The Causes of Eczema

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Ep. 10: The Causes of Eczema

Nov 19, 2021
Eczema is a common skin condition that can affect all ages. You may have even had eczema as a child before growing out of it! In this episode of Skincast, Dr. Johnson and Dr. Tarbox explain what causes this uncomfortable condition (and what does not). Tune in again next week to learn more about treatment options.


Dr. Tarbox: Hello, and welcome to "Skincast," the podcast for people who want to learn how to take the very best care of the skin they're in. This is Michelle Tarbox. I'm an associate professor of dermatology and dermatopathology at Texas Tech University Health Sciences Center in beautiful sunny Lubbock, Texas. And joining me is . . .

Dr. Johnson: Hello. This is Dr. Luke Johnson. I am a pediatric dermatologist and a general dermatologist with the University of Utah.

Dr. Tarbox: Today, we're going to talk about atopic dermatitis, more commonly known as eczema. Luke, as a pediatric dermatologist, I know you see a lot of patients with this condition, so what is it?

Dr. Johnson: I sure do. It's an itchy red rash, and it's common. There are a lot of things in the world of dermatology that could be described as itchy red rashes, so there are a few things about eczema that look distinct to a skin doctor, but maybe not so much if you don't spend all your days looking and thinking about skin.

It tends to be scaly. It tends to be what we call ill-defined, so it's kind of hard to tell where the rash necessarily starts and stops. It tends to show up in specific areas of the body, and those are a little bit different depending on how old you are, but it's especially common in babies and little kids. There are some medical data that says about one in five babies can get it. And then it's common in other age groups as well.

Dr. Tarbox: Yeah, the literature is about 15% to 20% of kids can have atopic dermatitis. The words eczema and atopic actually are kind of fun. So eczema comes from a Greek word ekzein, which is to boil over or breakout, and atopic means out of place. But really, it's just this eruptive, pruritic rash, this itchy rash, that little kids can get, and it can be so disruptive to their little lives, and as well to the family.

So what causes it, Luke?

Dr. Johnson: Well, what I sometimes tell the families who come in to see me is that if you look in a dermatology textbook about what causes eczema, you find a huge list of things. And you just told me that you wrote a chapter in a textbook about what causes atopic dermatitis. So not only is there a huge list of things, there's an entire chapter about it.

But I tell people that, in my opinion, the most important thing is that can cause it is that the skin is leaky. So one of the most important functions of the skin is to be a barrier between your insides and the outside. And in people with eczema, it's leaky, so it's not as good a barrier. And because it's leaky, water can evaporate away. So people with eczema tend to get dry skin, and then other stuff can get in through those leaks that's irritating and creates the itchy red rash that we see as eczema.

Dr. Tarbox: I love that explanation, Luke. And I think that that's such a nice way to encapsulate it for families. We know from looking at the science that it's caused, in some patients, by a mutation in a gene that helps make the outside of our skin more waterproof. If we lose that waterproofing and we do have leaky skin, we have to remember that water always flows downhill, even microscopically. There's more water in our skin than there is in the surrounding air, and so we lose water through our skin to the air and then other things get in.

Things that can make that worse are an even more dehydrated internal air environment, like what happens in the wintertime when we turn on the heaters and the air becomes dehydrated, as well as a contaminated environment with lots of particulate dust.

Dr. Johnson: And I sometimes have people say, "Well, why does my child have this leaky skin whereas other people don't?" And the unsatisfying answer that I give to a lot of people who have questions about why this happened to them is, "Well, mostly it's bad luck." But what it probably is, is a combination of genes and probably some other factors as well that just came together in this particular configuration, sadly in your child, so that he or she has eczema.

It's not a traditional genetic disorder, so it's not like, "Oh, my dad has it and my grandpa has it. Now I have it." It's more like there is a combination of genes, and if somebody in particular happens to get the right combination, then they are more prone to this kind of issue.

Dr. Tarbox: We also find that some things that mess up what we call our skin barrier, that waterproofing of the outside of our skin, can make eczema worse. Harsh detergents can do this either in clothing or in the products that we use to cleanse skin. Sometimes things that we apply in an effort to improve the eczema can cause problems if it's got irritating chemicals or things that we're allergic to in them.

And then we also wonder about immune dysregulation. Have you seen some flares of eczema in kiddos that have had to deal with the COVID virus?

Dr. Johnson: I don't know about the COVID virus in particular, but it's pretty well known that if kids get a cold, just like an upper respiratory tract infection, their eczema tends to get worse for sure.

Dr. Tarbox: The immune system plays a role. The environment plays a role. And then patients' contact with any kind of chemicals or anything that makes an irritation to the skin also plays a role.

Dr. Johnson: There are other skin diseases that can sometimes be mistaken for eczema: psoriasis and, of course, there are lots of others as well. So I admit I did not know what psoriasis was until I went to medical school. I kept getting it confused with cirrhosis, which sounds the same, but it's completely different. That's a liver disease. And so sometimes I have patients who come in and tell me they have psoriasis and, actually, they have eczema.

It's also not an allergy. So I feel like I have lots of patients and parents who feel that their eczema or their child's eczema represents an allergy to something. And it's true that kids with eczema have more allergies than kids without eczema, but the eczema itself is not an allergy.

Dr. Tarbox: And some of you may know that Mr. Dr. Tarbox is an allergist, so we spend a lot of time talking about this particular interplay of different kinds of medical conditions. When we're talking about a rash from food allergy, that's usually something that makes hives. Some people call them welts. Sometimes we call it urticaria. This is a different kind of rash than eczema is. It's more come-and-go very quickly type of rash than eczema is. So foods can cause a rash but not specifically eczema. What about . . .

Dr. Johnson: There's been a lot of research into food and eczema. So I find that it's pretty common for parents to wonder if it's something about the diet that affects the child's eczema. And again, there's been a lot of research and the general answer is no, there's nothing about the diet that affects their eczema, which I know in some ways is kind of disappointing because we can control our diet.

And I think one reason that there are a lot of people who really want the diet to play a role is because eczema is by its nature uncontrollable. It comes and goes, sometimes for a good reason, like it's dry in the wintertime, and sometimes for no good reason, it's just there. And there's a tendency to want to say, "Oh, well, it's because of something I did," like feed him peanuts yesterday, or whatever. But really, it was just a coincidence.

And while we can control our diet and it doesn't help, we can control what we put on the skin, the sorts of soaps and stuff we use, and other things that we'll discuss. But I do want to reassure people that in the vast majority of cases, the child's diet or the breastfeeding mother's diet is not related to the eczema.

Dr. Tarbox: Now, one thing parents can be in control of that can influence the severity of eczema is cigarette smoking in the house, especially because the particulate debris that can come out from smoking and the contaminants that can end up in the clothing fibers and on the carpet and on the child's skin have been proven to potentially exacerbate eczema.

So if you do have a child with eczema, trying not to smoke around them and trying to keep any clothing contaminated with cigarette smoke away from them could be beneficial.

Dr. Johnson: Eczema is also not anyone's fault. It's not because of something that you did or didn't do during pregnancy, or something that you did or didn't do while taking care of your baby. There are things that can make it worse, like smoking, and there are things that can make it better, like moisturizing the skin. But to current medical knowledge, there's really nothing you could have done to have prevented this.

Dr. Tarbox: So, Luke, when a parent comes to you with a small child that has eczema and they're looking at you with that look of desperation in their eyes, that question that's unasked, "Is it always going to be this hard to take care of this kid's skin?" what do you tell them?

Dr. Johnson: It's definitely a lot of work. And when I have a child with bad eczema and then they're better at follow-up, I make sure to tell the parents a lot of the reason that they are better is because of your hard work. It's definitely hard work.

The good news is that about 50% of kids outgrow it at some point. The earliest that tends to happen is around age 2, though for most patients, it's more like middle school age, so maybe age sort of 10 to 12 they start to outgrow it.

And the genes don't change. So what is it that changes that makes some people outgrow it? Well, we're still sorting that out as doctors. We don't really know. But because the genes haven't changed, if you were prone to eczema as a kid, there's probably something about you that's still prone to it even later in life.

So it's not uncommon that I have an adult patient come in or a teenager and it looks like they have eczema and they say, "Well, yeah, I think I had eczema when I was 3, but I haven't had it for 20 years. What's the deal now?" And to them, I say, "I'm sorry, I don't have an answer as to why this suddenly came back, but it is something that we see."

Dr. Tarbox: One reason we think that kids outgrow eczema is that there's this compound that gets formed in the outside layer of the skin that's appropriately named natural moisturizing factor. And small children don't form it well in all areas of their skin, specifically the areas where they tend to get bad eczema like their cheeks. So it takes them a while to start forming that uniformly over their skin.

And it's formed from that same gene that sometimes gets messed up in patients that have atopic dermatitis or eczema, which is called filaggrin. And whenever this is present, it improves the health and quality of the skin. So researchers are actually looking at replacing it synthetically to try and help improve the skin in patients that have atopic dermatitis.

Dr. Johnson: Finally, I want to point out that we cannot diagnose eczema with any kind of test. The good news is we generally don't need to. Eczema generally looks pretty obvious to most skin doctors and probably a lot of pediatricians and other sorts of doctors as well. So we don't need testing to diagnose it.

You can take a biopsy of the skin where you cut out a little piece and look at it under the microscope. That's not necessary in the vast majority of cases because, usually, eczema looks like eczema and we can figure it out.

But just like the fact that it's not an allergy, we can't do allergy testing, for example, to sort out eczema or to figure out whether or not your child has eczema.

So the best test is to have a doctor look at you or look at your child and listen to the history and figure out if it looks and sounds like eczema.

Dr. Tarbox: One of the good things too is that we know more about it now than we have ever before in history and we have more therapeutic options than we did previously.

So on our next episode of "Skincast," we're going to discuss ways to help treat patients that have atopic dermatitis or eczema.

Dr. Johnson: Stay tuned for that, and thanks so much for hanging out with us today, guys. And thanks to the University of Utah for supporting the podcast, and to Texas Tech for lending us Michelle.

If you are a super dermatology nerd, you might be interested to know that Michelle and I have another podcast. It is called "Dermasphere." It's really intended for other dermatologists and people practicing dermatology, but again, if you're a super dermatology nerd, maybe you'll find it fun as well.

We'll see you guys next time.