what is contact dermatitis

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If you've ever wondered, “what is contact dermatitis?” — you're in for a treat because this episode is going to blow your mind!

My guest Dr. JiaDe (Jeff) Yu lectured on contact allergic dermatitis at the Eczema Expo 2023 hosted by the National Eczema Association, and I found his presentation so valuable that I invited him here to share the ins + outs on the topic.

We covered a ton of information, but what I can say is that contact dermatitis is complex!

Allergic contact dermatitis isn't like a traditional allergy in specific ways (especially when it comes to using antihistamines to get things under control).

There's unfortunately a significant issue with both false positive AND false negative results from testing. AND how to treat contact dermatitis will vary depending on several factors (like whether it's a topical problem versus a systemic one).

If you aren't familiar with Dr. JiaDe (Jeff) Yu, he's an Assistant Professor of Dermatology at Harvard Medical School and a dual board-certified adult and pediatric dermatologist practicing at the Massachusetts General Hospital in Boston, MA. He is the Director of Occupational and Contact Dermatitis Clinic and the Associate Director of Clinical Trials. He has a niche interest in pediatric allergic contact dermatitis and has published numerous peer-reviewed articles on allergic contact dermatitis and atopic dermatitis in leading dermatology journals. He has received numerous research grants from the Dermatology Foundation, American Contact Dermatitis Society, and the Pediatric Dermatology Research Alliance to better understand the biomedical underpinnings of allergic contact dermatitis. Dr. Yu is the President-Elect of the American Contact Dermatitis Society and has been invited to lecture nationally and internationally on his areas of expertise.

Have you had any personal experience with contact dermatitis? I'd love to hear your story, comments + questions on this topic in the comments below!

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In this episode:

  • What is contact dermatitis (and is it genetic)?
  • Contact dermatitis compared to food or environmental allergies
  • Which antihistamines don't work for contact dermatitis
  • Top contact dermatitis allergies
  • The antibiotic that's a common allergy
  • If you're reactive to medical gloves…
  • Crazy “hidden” sources of contact dermatitis allergens
  • Testing for contact dermatitis (beware of your results)


“When you do get a cut or a scrape, the skin barrier is physically damaged, therefore allowing the introduction of new allergens into the skin. So when you put on a triple antibiotic, which includes three different antibiotic components, neomycin, bacitracin, as well as polysporin, you give your body the opportunity to learn about these allergens and then become allergic to them.” [10:03]

“Disperse dyes are the most common thing that causes contact dermatitis in clothing- specifically disperse blue dyes.” [20:50]

“Vitamin B12 is very high in cobalt because vitamin B12 is also known as cobalamin and in the middle of it, there's a cobalt molecule. So, people who have high doses of vitamin B12 can actually get a rash due to the ingestion of cobalt if they have cobalt dermatitis.” [24:39]


Follow Dr. Yu on Instagram | Twitter

Dr. Yu's clinic: The Contact Dermatitis & Occupational Dermatology Clinic

Healthy Skin Show 114: Why Preservatives In Skincare Can Be A Good Thing w/ Rachael Pontillo

Healthy Skin Show 246: Everything You Need To Know About Skin Tests (Done By Your Dermatologist) w/ Dr. Peter Lio

Healthy Skin Show 229: Lanolin Allergy + Vitamin D

Healthy Skin Show 037: Nickel Allergy And Eczema w/ Dr. Peter Lio


315: What Is Contact Dermatitis? (Triggers, Testing + Treatment You Need To Know) w/ Dr. JiaDe (Jeff) Yu {FULL TRANSCRIPT}

Jennifer Fugo (00:07.363)

Hi, Jeff. Thank you so much for being here. I'm excited to have this conversation today and to welcome you to the show.

Dr. Jeff Yu (00:14.562)

Thank you, I'm so glad to be here to talk about what is contact dermatitis!

Jennifer Fugo (00:18.999)

I know. And so we actually met at the Eczema Expo 2023, where I saw you lecture and I learned so much from you. So thank you, first of all, for being on the show. My audience has loved all of the information that I had shared from your presentation and had so many questions. So I figured this was the perfect opportunity to actually ask you because I feel like… I don't know, the allergy world, and then we get into rashes and all this stuff, it sometimes feels overwhelming to somebody like myself or maybe to patients who probably don't know all the things that you know. So why don't we start off with what is contact dermatitis, and how is it different from something like eczema or hives, or is it the same thing?

Dr. Jeff Yu (01:08.374)

Yeah, that's a great question. And I don't even think it is a difficult topic for patients to understand. I think it's a difficult topic for doctors as well as even dermatologists who are not as involved in this area of study as say some people who are in patch testing are.

So what is contact dermatitis? Very briefly, it is a type of allergic reaction your skin manifests to things it comes in contact with. So for example, poison ivy being the best example of contact dermatitis that most of us who are living in the United States understand all too well is when you come in contact with poison ivy, you develop a rash. Now, if you see poison ivy across the road, unless you go ahead and touch it, you're probably not gonna develop that reaction from just smelling it or from looking at it, but it's really something that the leaves itself and the oils that are exuded from the leaves have to brush up against your skin, and at which time your skin's immune system starts to develop a reaction and says, hey, I don't like this, whatever it is I'm coming in contact with, so I'm going to start sending out some white blood cells there that's going to create a reaction that oftentimes looks like eczema. So it's going to look red, it's going to look scaly, it's going to look, you know, rashy for lack of a better word, and sometimes even blistery on that area. Now, the interesting thing about contact dermatitis is that, unlike seasonal allergies, for example, like pollen or even environmental allergies to things like cats and dogs, this reaction doesn't happen immediately. So it's not like you're gonna go hiking today, touch poison ivy and develop a reaction within a few minutes. It's something that develops within hours, sometimes even days after exposure, making it really difficult to kind of figure out what it is that you came in contact with. And that's because the immune system takes about that amount of time to really generate this reaction to something that you come in contact with, something like poison ivy, for example.

Jennifer Fugo (02:55.715)

And you can be not allergic or not have contact allergic dermatitis issues with poison ivy. I don't get it, but my mother does. So this is, I assume, not a genetic or hereditary problem.

Dr. Jeff Yu (03:10.386)

It is not a hereditary problem. We see a lot of parents who bring their kids in and say, oh, I'm allergic to so-and-so, so my kid must be, but that's not always the case. And we don't really know what causes someone to develop contact dermatitis. All we do know is that your body must have seen it before. A good example of that is, like I said before, in the United States, people have poison ivy allergy on the order of probably some 80-some percent, mostly because poison ivy, poison oak, or poison sumac is so indigenous to this area that we live. Whether you're on the East Coast, the West Coast, or the Midwest, it doesn't really matter. Poison something is out there. But in other countries in the world, one example being Israel, for example, they don't really have poison ivy or any of the poison plants. So therefore people who live there and grew up there are not allergic to poison ivy at all because their body has never seen it. So it's certainly not something where your mother and father have a reaction to and you're gonna develop a reaction to just because you're related to them. It's purely dependent on whether or not you've been exposed to it and your body has had the chance to learn it and then develop a reaction to it.

Jennifer Fugo (04:15.715)

And contact dermatitis is not the same as a food allergy. Is that correct?

Dr. Jeff Yu (04:20.53)

It is not the same as a food allergy, mostly because of the type of reaction that occurs. So thinking about environmental allergies and food allergies, those are mediated by cells and molecules in your body called histamines. So this is where you're thinking about things like antihistamines can benefit you. So in the springtime, you have a pollen allergy, you take some Zyrtec, you take some Claritin, you take some Benadryl. One of those antihistamines, your symptoms get better.

Contact dermatitis has nothing to do with histamines at all. It's actually dependent on a special type of white blood cell in your body called T cells. And these T cells then will eventually come out, check out the allergen, and then start generating a reaction that takes on the order of days, not minutes. And then the only treatment for contact dermatitis is number one, avoidance of whatever it is that you're allergic to. And then number two, treating it with some sort of an anti-inflammatory medication such as topical steroids, oral steroids, or various other medications that we have in our armamentarium to treat these types of allergic reactions. But antihistamines, in general, do not do anything for contact dermatitis.

Jennifer Fugo (05:29.443)

So if you tried, say, Benadryl, and it didn't help, could that be a helpful clue to tell your dermatologist?

Dr. Jeff Yu (05:37.458)

100%. So when people come in and I see a lot of patients for evaluation of contact dermatitis, one of the questions I ask them is, you know, have you tried taking an antihistamine for this and does it work? If they say it does work, then immediately my mind shifts from maybe this is not contact dermatitis to maybe this is either those seasonal allergies or environmental allergies or a different type of allergic reaction. And therefore, what I do to evaluate for contact dermatitis patch testing may not be appropriate for these patients.

Jennifer Fugo (06:07.835)

Fair enough. I think that's actually very helpful tidbit. A lot of times, people sometimes who want to go the more integrative route get really nervous about trying medication. But I am of the mindset that everything serves a time and a place and serves a purpose. And sometimes, something like this, this could actually be really helpful in you as their physician figuring out what's actually going on. So I think that is a really important tip for everyone to hear.

Now, in turns of common allergens that could cause a problem. We mentioned poison ivy already. What are some of the other top common allergens that you see in terms of contact dermatitis?

Dr. Jeff Yu (06:49.27)

Yeah, by and large the most common contact dermatitis allergen other than poison ivy in the United States as well as everywhere else around the world is a metal called nickel. And some of you all may be familiar with that already but nickel tends to be a cheap silvery type of metal that is oftentimes found in costume jewelry. So guess where the exposure is, right? Cause remember contact dermatitis has to come from exposure sources from somewhere. So the most common exposure for nickel allergy for most people tends to be from body piercing, whether it is the cheap earrings that you wore when you were four years old, or the watch that you wore, or the belt buckle, or the jean snaps, or somewhere that's made from nickel, your body has ample opportunity to learn about this metal and then potentially say, hey, I don't like it, so I'm gonna develop a reaction to this.

So the most common places people develop reaction to nickel, if you are truly allergic would be say, oh, my earlobes get itchy after I wear a cheap piece of costume jewelry or my neck gets itchy after wearing this necklace that I found at some sort of a night market or my wrist always gets itchy when I wear a particular watch or most commonly right under my belly button, I get a rash probably from your jean snaps or your belt buckle or something. So those are by far the most common sources of exposure and nickel is really used everywhere from your clipboard to your keys to coins and whatnot. So plenty of opportunities to become allergic to nickel.

Jennifer Fugo (08:14.039)

What about metals? Is it possible to have contact dermatitis to metals like chromium and cobalt?

Dr. Jeff Yu (08:22.862)

Nickel and cobalt both occur oftentimes together. So for a lot of people who are allergic to nickel, they're also allergic to cobalt. I think chromium probably a little bit less common, even though easily one of the top 20 allergens, but a little bit less common just because chromium as a metal itself is used in things like orthopedic implants, but less common in things like jewelry, for example. So I think there lies the lack of exposure for a lot of people. But chromium allergy though, we often see in the setting of cements because a lot of cement has chromium in it. So we'll see construction workers with feet rashes that may be related to the cement that they're pouring or hand rashes that may be related to the cement. And then sometimes in leather. So a lot of leather is made using chromium processing and therefore we'll see rashes on people's feet, on people's hands, for example, that are wearing leather shoes or leather gloves.

Jennifer Fugo (09:20.867)

What about antibiotics? I had this really fascinating experience. My sister-in-law had gotten what she thought was a cut. She put like one of those triple antibiotics on it and it got worse and worse and really inflamed and looked like it was crazy infected and she got really nervous. It turned out she was actually reacting to the antibiotic!

Dr. Jeff Yu (09:43.266)

Yeah, big, big problem. I think in the US, triple antibiotic, as you said, is easily available over the counter. And I think the companies that make triple antibiotics do a really good job advertising, right? Like every time you fall, put some antibiotic on there and it's gonna make things better even though the wounds themselves are not infected. And because when you do get a cut or a scrape, the skin barrier is physically damaged and therefore allows for the introduction of new allergens into the skin. So when you put on a triple antibiotic, which includes three different antibiotic components, neomycin, bacitracin, as well as polysporin, you give your body the opportunity to learn about these allergens and then become allergic to them. Neomycin is, by far, the most common antibiotic allergy, followed by bacitracin, not surprisingly because the two often occur together.

And triple antibiotic is one of the most common reasons why I see, oh, my cut is getting worse, it's getting more infected, or my surgical scar looks like it's getting infected and whatnot because people have been putting these antibiotics on those wounds thinking that it's going to help, but instead it makes it look worse. We certainly have patients have to go back into the operating room for things like orthopedic surgery because they thought maybe the wound was getting infected; they need to go clean it out and whatnot. We've had people get fingers amputated because they thought it was just getting worse in an infection, but at the end of the day, it's all because of an antibiotic allergy that wasn't picked up, because most people don't think about it very much, right? Like you have a cut, it looks like it's getting worse, common things being common, maybe the infection is spreading and getting worse, so things like that can definitely happen. Now not common, but definitely can occur.

Jennifer Fugo (11:26.191)

Wow, and for the healthcare workers who listen to the show, there are many who also tend to struggle with hand kind of rash issues, hand eczema, dyshidrotic hand eczema, et cetera. What about the nitrile gloves? Could they be a problem for some, especially if they have contact dermatitis on hands?

Dr. Jeff Yu (11:42.402)

Mm-hmm. So a lot of people think about latex, right? Latex is something that we understand really well, we hear about really often, because back in the 70s and 80s, there was pretty much an epidemic going around of people developing allergic reactions to latex gloves. Now, by and large, latex is no longer being used in the healthcare industry for gloves because of that. So most of the gloves you're gonna find are non-latex or latex-free. But that doesn't mean they're free of rubber. And I think that is a common misunderstanding is that latex is a type of rubber, but there are many other types of rubber out there that are still used to make gloves. Anything that is stretchy and that can fit well to your hands, anything that is water resistant and whatnot, they're all made out of rubber. They're just not latex, but they're still rubber. So nitrile gloves, for example, neoprene gloves, for example, these are all common gloves that are used by the doctors and the nurses in the clinic, in the OR and whatnot. They're all still rubber.

And rubber allergens are not uncommon causes of contact allergic dermatitis. And these rubber allergens are coming from the processing of gum rubber. So you extract the rubber from the trees and you have to process it. And they use something called accelerators. And these rubber accelerators speed up the process to make these finalized useful products that people can use, whether it's gloves, whether it's shoes or whatnot, that still are gonna contain rubber. And then people can develop an allergic reaction to them.

So there are gloves out there that are rubber accelerator-free, and those gloves are going to be safe for people who are allergic to rubber in the more common nitrile or neoprene gloves. So we've had people having to switch careers because they had such bad hand dermatitis and they can't find a pair of gloves that works for them because they've never seen someone for patch testing and they never got the recommendation. But we do see healthcare workers come through and we definitely help them find the appropriate pair of gloves that can serve them better.

Jennifer Fugo (13:40.311)

I loved that you were able to answer this question because I've gotten it so much. And so I hope, I mean, we have so many nurses, especially those who work in the hospitals who listen to the show. So I'm hoping that those who are really struggling with this, because obviously you don't like we need our healthcare workers and we need your hands to be able to bend and move without pain and whatnot. And it's just so sad to hear the stories of people who are really struggling because their hands are just such a wreck. That's really great, I hope that this helps somebody. All right, so I'm gonna ask you, I'm hoping I don't butcher this word, but I see this online, and I'm sure many of you have seen this ingredient, and perhaps don't know how to pronounce it. So, methylisothiazolone.

Dr. Jeff Yu (14:29.674)

Great job, that's perfect. As good as I've heard it pronounced by anybody else. Yes, so methylisothiazolinone is something that people have never heard of 10, 15 years ago. And this is an example of where exposure is really important for the development of contact dermatitis. 10, 15 years ago, methylisothiazolinone used to be bundled together with another chemical called methylchloroisothiazolinone. Now they both sound similar because they're related in a way and they used to bundle them together and they use them as preservatives in products. So people often ask me, oh, I use a shampoo with no preservative. You know that's not true. The reason you know that's not true is because if you imagine your bottle of shampoo, it was probably sitting on a container ship for a few months. Then it sits on a store back room for a few months, then it sits on the shelf for a few months, and then you buy it. And then you put it in your shower for maybe a year before you finish using it. At some point of that process, if it didn't have any preservatives, you would be using moldy shampoo, right? Like that would be a fact. There's no way you can prevent bacteria, mold, and viruses from growing in that environment. So every product that has a shelf life needs to have a preservative.

And different preservatives serve different purposes. There are some preservatives that are really good for bacteria, viruses, mold individually, while some are really good for all three of those things. And methylchloroisothiazolinone and methylisothiazolinone are preservatives that do a really good job fighting against all three of those pathogens.

So companies like using it because it gives their products number one, safety for human use, number two, a shelf life. So they can, you know, it doesn't have to be removed after a few months and they have to restock it if it doesn't sell, they can leave it on there for a few years and it will still be okay. So the problem with this is that back in the day, in the early 2000s, people started to notice that there were a lot more people developing contact dermatitis to this bundled component, a methylchloroisothiazolinone and methylisothiazolinone.

Then what they thought would be really wise to do would be, well, maybe the methylchloroisothiazolone was the problem, so they got rid of that part and just used methylisothiazolone by itself. The problem with that is, in order to have the same antibacterial and antimicrobial properties, they needed to use much higher concentrations of methylisothiazolone, which is abbreviated MI. So what happened was they started using much higher concentrations of MI in different products. And then lo and behold, starting around the mid-2000s to the mid-2010s, you started to see this, the number of people developing allergy to MI slowly creep up. And right now, at least the most recent data that we have on the prevalence of contact dermatitis in the United States and Canada is that MI is the number two most common thing that people are now allergic to, versus 10 years ago, you wouldn't even have found it on the list.

So right now it goes nickel and then very close behind it is going to be MI just because of the fact that it was used so widely in all these products, including things like baby wipes. So there were a series of children who developed really bad face rashes to MI, butt rashes to MI, things like that. They don't use it anymore, but at one point it was definitely used very frequently. Sunscreens used to have MI in it, so people would develop a reaction to that.

Now, MI is largely restricted to rinse-off products. What that means is shampoos, conditioners, soaps, things that are meant to be rinsed off but not left on the skin, hoping that it would decrease the likelihood of people developing a reaction. Still number two, last time I checked. So it is something that is still a problem and continues to be a problem, but it's really related to its exposure.

Jennifer Fugo (18:25.163)

And you can't trust a product that is quote, free and clear. Could you say that it won't have MI in it, or that has nothing to do with MI?

Dr. Jeff Yu (18:34.646)
That has nothing to do with MI. A lot of these free and clear labeling is really meant to be number one, doesn't have color, so it doesn't have a dye to it, and number two, free of fragrances. That's usually what they mean, not necessarily free of preservatives, because again, there's no way that these products can survive without preservatives.

Jennifer Fugo (18:52.975)

Fair enough. I also wanted to ask you quickly about disbursed dyes. And you mentioned also in your talk about formaldehyde being treated in clothing. I never heard of that. It's like crazy the areas that some of this stuff shows up in. Can you just touch on this briefly for anybody who might be wondering what the heck's going on when they are exposed to certain types of clothes?

Dr. Jeff Yu (19:17.302)

Yeah, so clothing dermatitis is not the most common form of contact dermatitis, but we certainly can see it. You know that you might have a problem to your clothing if you wear a particular clothing and it gives you a rash. Now, not if it makes you itch. And I make this clarification because I have a lot of people who come in and see me with eczema. And if you have eczema, you have “sensitive skin”, meaning your skin is more highly irritated by certain things, especially clothing that may have a little bit coarser fabric namely things like wool. So a lot of people come in and say, oh, I'm allergic to wool. Well, you're not really allergic to wool. Wool just irritates your skin and that makes you itch. Just like the tag on a shirt might irritate the back of your neck, it's not truly an allergy. It's more of you developing a irritant reaction or itching because of that fabric.

But there are some people who truly are allergic to their clothing and those locations tend to be armpits where the clothing sits tighter, in the hips where the clothing sits tighter, on the thighs where the clothing sits tighter, especially along the belt line where the clothing tends to sit a little bit tighter. In those areas, people can certainly develop an eczema-like rash, so red, scaly, itchy, to the clothes that they wear.

Disperse dyes are different types of dyes that are used to color clothing, as the name suggests, but they are only used to color synthetic fabrics. So, polyester, rayon. And you know fabrics that are man-made as opposed to say wool, cotton, silk. Those are more natural fabrics and do not contain dispersed eyes even if they are colored in some way- they use different types of dyeing techniques. Dispersed dyes are the most common thing that causes contact dermatitis in clothing- specifically dispersed blue dyes. My shirt is blue, but if my shirt is a hundred percent cotton, it doesn't matter if it's blue. It's not going to have dispersed dyes in it versus if it's 50% polyester, it IS going to have dispersed dyes of some sort.

Formaldehyde is also used to treat clothing specifically for clothing that are meant to be wrinkle-free. So if you have a dress shirt that you can throw in the dryer and it comes out crisp, like it's been ironed and it hasn't been ironed, that probably contains formaldehyde or it contains some sort of a formaldehyde-based resin that is going to make clothing look starchy, and it looks permanent press. It looks nice when it comes out because they treat the fabric in a certain way. So things that are super wrinkly when they comes out are probably formaldehyde-free. Things that are very nicely pressed when it comes out, probably full of formaldehyde. School uniforms, you know, like airline uniforms, military uniforms, definitely full of formaldehyde because they all just are made to look a certain way. So those are things that can certainly cause reactions as well.

Jennifer Fugo (21:56.367)

Wow. Oh my gosh, so many things to look out for. See, this is why bringing a doctor like you more information is probably helpful, because if you're wearing, like you said, cotton, silks and more natural fibers, that might help you rule certain things out. I did want to ask just very quickly about diet and nickel. We've obviously had Dr. Peter Lio comment about this a few years ago, but what's your take? I see these people online telling people you gotta remove nickel from your entire diet that's the cause of all like dyshidrotic hand eczema and all this other stuff. What's been your experience do you really need to go that far to avoid nickel-free foods which by the way is a pretty extensive elimination diet.

Dr. Jeff Yu (22:43.842)

Yeah. So, um, I definitely believe that systemic allergic contact dermatitis is real. What that means is that if you have contact dermatitis to something- nickel, chromium, cobalt, an allergen called balsamic Peru, which is a fragrance allergen- there are, there is a small subset of those people who are positive and allergic to these allergens that could also develop systemic reactions when those allergens are ingested. Now it might be counterintuitive to think “why is there nickel in my food?” I'm not eating anything that's hard and metallic, but nickel is one of the elements that's in our soil. So certain types of foods are very high in nickel. Things such as oatmeal, for example, is very high in nickel. Certain types of whole wheat breads, bran, things like that can be high in nickel. I always educate my patients when they're nickel allergic.

Number one: Is the distribution of their rash likely to fit a systemic contact dermatitis to nickel? You mentioned dyshidrotic hand eczema. Absolutely, that's one of the reported types of potential allergic contact dermatitis reactions to nickel. People can develop a full-body eczema-like rash and those patients I do mention, maybe nickel could be doing it. But the subset of those patients is very, very small. So out of 100 patients, I would say somewhere between five to 10, probably benefit from nickel avoidance, so less than 10%, whereas 90% of them are more likely to be topical contact as opposed to systemic ingestion.

So, you know, sometimes I feel like I go for a few months without ever seeing anybody with some sort of an ingested allergen, but recently I had two people who actually had systemic cobalt dermatitis, which is kind of interesting. Cobalt can be found in foods like shellfish, for example, coffee, teas; things like that can be high in cobalt. Vitamin, so specifically vitamin B12 is very high in cobalt because vitamin B12 is also known as cobalamin and in the middle of it there's a cobalt molecule. So people who have high doses of vitamin B12 can actually get a rash due to the ingestion of cobalt if they have cobalt dermatitis.

One kid had eczema just around his eyes. We didn't find anything else that was relevant. We found that he was cobalt-positive. Mom mentioned he drinks a lot of energy drinks, just as kind of a side kind of thing. And then you figure out that in his energy drinks, there was a lot of vitamin B12, and he was knocking down several of these every single day. So he was ingesting a ton of vitamin B12 which has cobalt in it. Once he got rid of that, his eyes completely cleared up. So that was one example of where, you know, why just around the eyes? I don't know, but he definitely got better because of that.

And another woman who had bariatric surgery also takes high doses of vitamin B12 because after bariatric surgery, you start losing your ability of absorbing vitamin B12 in a part of your gut. So she was taking 50 plus thousand percent daily value of vitamin B12. She developed this rash right afterwards. And then we talked to her nutritionist, we talked to her bariatric surgeon, we got her down to just the 100% daily value of vitamin B12 and her rash significantly improved from that. So because of some of these patients that I do see, I definitely believe it's a real thing, but I think it is a special case situation only, not a “we should do this” for every single patient because it is hard to do. It is harmful, I think for some, especially for children. And I tell people, if you're gonna try it, try it for a month. If it doesn't work at the end of a month, don't do it anymore.

Jennifer Fugo (26:18.363)

Fair enough. Well, let's talk about testing before we wrap up because I do think that this is important. So how do you get tested for this? You mentioned before briefly about patch testing. So how does this work?

Dr. Jeff Yu (26:30.646)

Yep, so testing for contact dermatitis is very different than your traditional allergy testing that I think a lot of people have been through. Traditional allergy testing puts little droplets of allergens on your skin. They take the stylus and they kind of scratch your skin with it and you look to see if you develop a hive. Now what they're looking for is a histamine-based reaction, but remember contact dermatitis has nothing to do with histamine. So for patch testing, we put patches on your back and each patch contains a different allergen- whether it's nickel, whether it's formaldehyde, whether it's disperse dyes, whether it's methylisothiazolinone or one of these allergens, we put them on your back and you go home. You go home with those patches on because we're leaving those patches in place to expose your body to it for 48 hours. You come back two days later, we take the patches off, and you go home again for the next 48 hours, and then you come back because what we're doing is we're giving your body 96 hours to develop this reaction because this reaction takes time to show up. If you're only gonna look at the results in 24 hours, you're probably not gonna see anything because that's not enough time for your body to really rev up its immune system and create the positive reactions that we're looking for. So 96 hours, somewhere around there is the optimal time point to look for positive reactions.

It is difficult to do just because you have to come into the office three times during that week. You can't get your back wet because that's where we typically put the patches on. So we tell, so a lot of people end up not showering during that period of time, but they can wash everything else. And, but this is really the only way to look to see if you have contact dermatitis to something or not. There are no blood tests that are available. There are no other tests that are available of testing for these allergies.

Jennifer Fugo (28:11.659)

And can you have maybe a positive reaction on the skin, but not actually react to it, or maybe not have a reaction at all, but maybe use this like false or negative, false negative or positive, false negatives or false positives? Are either of those possible with this?

Dr. Jeff Yu (28:29.47)

100% we see people who are positive to things and they're like I've never had a reaction to this and I tell them, “Don't worry about it because I think with patch testing I think anybody can put patches on a patient and take a look for the results and say you're allergic to X Y and Z I think our job isn't really just saying this is what you're positive to our job is really saying this is what you're positive to and why this makes sense or why this matters, and more importantly, how do you avoid this so you can get better with your rashes? And a lot part of my job is the counseling aspect where I say, does this positive reaction make sense? Do you need to actually avoid this or not?

Jennifer Fugo (29:08.203)

And then with young children who are tiny and might not fit a large panel, how would they, do they have to go back multiple times to get tested?

Dr. Jeff Yu (29:16.034)

So we do our best in terms of picking the things that are most relevant. I just had a three-year-old this past week where I was only able to fit about 20 things on this patient. So I put 20 different patches on her to see if she was positive to anything. And I picked those 20 based on what she was currently using at home that mom and dad was able to bring in to show me. For the average adult, we'd probably test somewhere between 80 to 150 different allergens. And that can easily fit on your back, as an average size adult.

And I think the more we test, the more likely we are to find what it is because we don't know what it is that you're allergic to. And oftentimes, patients don't remember either. Sometimes I'll say, oh, you're positive to this. Have you ever used this before? They're like, oh yeah, I use it every day. But they just never thought to bring it up because it wasn't a medication or it wasn't considered, you know, or they thought, oh, I bought this from the organic store, so it must be okay. A lot of times patients are not, don't always remember what it is that they're allergic to unless you test them for it and you say, you know, could this possibly be the culprit?

Jennifer Fugo (30:12.827)

Yeah, and I think this is, I know I said that was maybe the last question, but can you grow out of this? Is this something where maybe if you have it as a child, you could as an adult be fine, or is this something that can come on as an adult that you never had as a child?

Dr. Jeff Yu (30:30.07)

Yeah. So people can develop this at any point in their life. I see kids, you know, down to a few months of age, who whose parents are suspicious for contact dermatitis to things like diapers and whatnot. And then I see adults in their eighties and nineties who've never had a reaction before and they develop a reaction. We don't know what causes you to actually develop contact dermatitis or why your body picks a certain time to develop those reactions. We know something is happening. We know something has changed. Sometimes I see patients who are like, oh, I went through chemo and radiation for my cancer, and now I have all these allergies I never had before. I went through menopause, and now I have all these reactions I never had before. I went through puberty, and I have all these reactions. Is it hormonal? Is it stress-related? Is it just a phase of your life? No idea. But people can definitely develop new reactions, and people can certainly grow out of reactions. We think that maybe from lack of exposure, people's immune systems eventually calm down and maybe unlearn those reactions. We don't know if that's true.

There was a recent publication looking at aluminum allergy. So they saw that younger kids had much higher rates of aluminum allergy, and then they tested the same group of people 15, 20, and 25 years later, and the number of people who had aluminum allergy really fell pretty significantly over time. So we do know at least aluminum allergy people can grow out of, is that true for fragrances, for preservatives, for metals, no idea. I think that really remains to be seen.

Jennifer Fugo (31:51.375)

I feel like we could talk about what is contact dermatitis all day. There are just so many questions!

Dr. Jeff Yu (31:54.487)

I do talk about it all day.

Jennifer Fugo (31:57.375)

I know you do. We'll have to have you come back. I'll think of more questions. And thank you so much. I love when guests come on and they are so giving and so willing to share their knowledge and help educate all of the listeners. And I'm just so appreciative that you made the time to come on the show. And I'm honestly thank you so much for being here. I appreciate it.

Dr. Jeff Yu (32:17.494)

Well, thank you for having me. I'm happy to talk anytime.

what is contact dermatitis