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Ep. 19: Understanding Itch

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Ep. 19: Understanding Itch

Mar 18, 2022

From bug bites to dry skin to poison ivy, there are a thousand reasons you might be itchy. In fact, just reading this sentence might be making you itchy right now! In this episode, Dr. Johnson and Dr. Tarbox discuss the various sources that make you scratch. Tune in next time to hear 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. My name is Michelle Tarbox. I'm an academic dermatologist and dermatopathologist at Texas Tech University Health Sciences Center in beautiful sunny Lubbock, Texas. And joining me is . . .

Dr. Johnson: Hello, everybody. My name is Dr. Luke Johnson. I'm a pediatric dermatologist and a general dermatologist with the University of Utah. And I'm itching to talk about some interesting subjects today.

Dr. Tarbox: Ba-dah-bum-bum. I love that. So, Luke, we're going to talk about itch today. Basically, we're going to talk about why we itch and maybe how to do something about that.

So why do we itch? Our skin is really a giant sense organ, and its biggest job, really, is to protect us from external threats. And really, any sensation in our body that's uncomfortable for us, anything we want to avoid in medicine, we call these nociceptive things, like pain or itch, are really there to protect us from potential harm. It is actually transmitted by a subclass of the same nerves that transmit pain.

So it's, like pain, a protective response and it's there to help us notice if, for example, there's a bug feeding on us, or if a parasite is attached to us, or maybe if we've got a skin infection, or we've come in contact with something like poison ivy or irritating plants that need to be removed from the skin.

So it can be helpful in the acute setting when we can maybe do something about it, like swat that mosquito, pull off that tick, or wash off the area skin that's infected and maybe treat it with something. It's also there to help us know when our skin barrier, that final frontier between us and the rest of the world, has a breach or is damaged.

Dr. Johnson: Why do I feel itchy just because you're talking about itch, Michelle? That doesn't seem right.

Dr. Tarbox: That's a great question. So the sensation of itch actually can be triggered by many things, one of which is our own imagination. So, if you think hard enough about being itchy, or if somebody around you says, "Oh, my dog has fleas" . . . As a dermatologist, we run into this when we treat patients who have the human itch mite scabies. We start to itch almost immediately after we recognize the other patient might have scabies because psychologically we connect that exposure to the risk of itching.

Dr. Johnson: That's something my assistants always say whenever we see a patient with scabies. We go back into our workroom and say, "Oh, I just feel so itchy right now."

Dr. Tarbox: Exactly.

Dr. Johnson: Does it work in reverse, though? Can I think myself out of being itchy?

Dr. Tarbox: There's actually some cognitive behavioral therapy where people can sort of think and distract themselves around the itch sensation to improve itch control. The reason you want to avoid it is because it is pretty darn miserable. In fact, the misery of itch and its ability to be almost akin to torture has been recognized since antiquity.

If you think about Dante's Inferno, there's actually a section of hell where people were punished by being left in pits to itch for all eternity. It was the falsifiers, the alchemists, impersonators, counterfeiters, and liars who were punished with the burning rage of fierce itching that nothing could relieve in the eighth ring of hell.

Dr. Johnson: Yikes.

Dr. Tarbox: Yes. In 1320.

Dr. Johnson: Also, in the Old Testament, the plagues on the Egyptians, there are a surprising amount of dermatologic plagues, including, I think, body lice, which are itchy.

Dr. Tarbox: Mm-hmm. And in the Bible, of course, they talk a lot about being in sackcloth or cilice. This is actually a garment made of coarse cloth or animal hair, like a hairshirt. And it was worn actually as a means of mortification of the flesh and an instrument to penance, because it made you itchy, which made you miserable. And that kind of made you realize your state as a human in this particular theology.

So there are actually even tribes in India that use itching as a punishment for social delinquents, like alcoholics and drug addicts. They actually put itchy substances on the skin in these very specific kind of applications. So there are all sorts of acknowledgment and understanding that it is miserable.

And all mammals scratch. So, if you've ever watched any mammals for any period of time, you've noticed them scratching themselves. Some researchers even believe that whales breaching the water is their version of scratching to help remove things from their skin.

So why do we scratch an itch? Itch is transmitted by that same subclass of nerves that transmit pain. When we scratch, it actually creates a low-level pain signal that overrides the itch sensation. This is something called gait control. Basically, if you can get an impulse to the spinal cord faster than another impulse, you can override that original sensation. So people do this with scratching. You can also do this with heat or cold.

Luke, why do we itch?

Dr. Johnson: Well, if you also move your finger there to scratch and distract your nerves away, maybe you find the tick or the mosquito or whatever it is. So you can understand why this would show up from an evolutionary standpoint.

There are lots of different reasons that people can itch, things that can activate those receptors, if you will. So an allergy to something or other is a big part of it. And people can get allergic to all kinds of things.

Michelle, your husband is an allergist, so he might take offense at how I will describe an allergy. But it's basically your immune system decides that something is a problem. And no one else's immune system thinks that, or at least the baseline human immune system disagrees, and it's really kind of not a problem for the most part.

But if your immune system decides, "Hey, peanuts are the bad guy," what can you do? Well, there are various ways you can tell your immune system to calm down. But getting hives, for example, is something that can make you itchy.

Getting bitten by bugs. So, technically, the reaction to a mosquito bite is a little bit of an allergy, because it turns out not everybody reacts. It's these sorts of immune cells that also react to allergies that we more commonly think of, to proteins in the insect saliva.

When we have one of these allergic reactions, then this particular type of white blood cell that's called a mast cell releases a bunch of stuff, including something called histamine, which most of us have heard of, which causes the blood vessels to dilate or get bigger. And then more white blood cells come to the area, which allows them to fix the breach in the skin or monitor to make sure nothing horrible is happening, but also can create more of this swelling and itchy response.

Other things can cause these mast cells to release their histamine and other products as well. So depending on what you're allergic to, it could be particular foods, it could be particular things in the environment, like pollen or pet dander. Some people are allergic to particular medicines. That's sort of the common denominator. The immune system gets angry and the mast cells release their stuff.

Dr. Tarbox: So I think that when we run into these itching conditions, it can cause some distress. And it can cause also sometimes trouble with sleep, sometimes trouble with focus, sometimes trouble with attention. And patients can really have a significant impact on their quality of life when they're dealing with chronic itching.

So what do you think happens when itch goes wrong, Luke? Have you ever seen any circumstances where that's occurred?

Dr. Johnson: Well, all the time. So in dermatology, we are the gatekeepers of itch. And so we have patients who are itchy, and many of them are miserable for the reasons you just described. And so one of our first stops on the dermatology train is to try to figure out what's causing it. Allergy is one thing.

There are lots of skin problems that can make you itchy, like eczema or psoriasis. One of the most common cause of itching, especially in older people, is just having dry skin. Dry skin can be surprisingly itchy. Fortunately, it's fairly easy to treat for a lot of people.

There are other things that can be coming into contact with the skin that can be irritating or to which people can develop an allergy. So there are different chemicals. There are things like harsh soaps. There are particular cosmetics that can do it.

We look for parasites. So you mentioned scabies. Scabies, sorry, listeners, is a little tiny bug that lives in the top layer of the skin and kind of burrows around and lays eggs and poops and makes you itchy.

Dr. Tarbox: In fact, you might be feeling itchy now.

Dr. Johnson: Yeah, just thinking about it. And then there are some other of these bugs that can cause itching. Body lice, for example, like we mentioned. There's something called pinworms.

Good news is that dermatologists and other health care professionals can usually identify these pretty well. So, if you think there might be some kind of bug causing you to be itchy, and the dermatologist takes a good look and says, "Good news, it doesn't look like I see any bugs today," you can feel pretty reassured that that's not what's going on, though presumably there's something else going on.

Pregnant women are more likely to be itchy than other people perhaps because of changes in the liver and the bile ducts.

Indeed, having other sorts of diseases in your various organs can make you itchy. So liver disease, kidney disease, thyroid disease can make you itchy.

And then sometimes when the nerves are acting in a wrong fashion . . . no offense, nerves . . . that can give people a sense of itch.

And dermatologists like to recognize that itch is kind of a broad term, and there are different types of itch. So, for example, you might have a deep burning itch, which can be more like it's related to the nerves, or we would say neuropathic or neurogenic in origin. Or you might have more of a superficial itch that feels more like your skin is dry or something. So you can tease out some of these to some degree, which is important because if you're aiming to solve the problem, you want to figure out what kind of itch somebody might have.

Dr. Tarbox: Exactly. And that's one of the things a dermatologist can help with, is trying to determine what might be the cause of chronic itching.

Some patients will have chronic itching for a medication reason. Some people will have it as a result of sort of that pathway, that circuitry that is in control of the itch-scratch cycle going wrong. In severe cases, it can even cause patients to have psychiatric distress or a psychiatric manifestation of chronic itching, which can be the concern that they have insects on their skin when they don't. Have you ever run into that, Luke?

Dr. Johnson: Yes. So if that's you out there, listener, you have our sympathy and we can help. Be open to options.

Dr. Tarbox: There are lots of . . . Oh, sorry. Go ahead.

Dr. Johnson: I was going to say speaking of options, there are a number of different treatments for itch. And I think we can talk about those in our next episode because there are enough of them that I want to be able to go into some detail about them. Some of them, even though they're not used by most people, are still pretty cool and I think worth getting into some of the details because they're neat.

So thanks for joining us for this episode on itch, listeners. If you're itching to hear more about itch, tune in next time.

Thanks to our institutions. Thanks to the University of Utah for supporting the podcast, and thanks to Texas Tech for lending us Michelle.

If you really enjoy listening to us, especially enjoy getting into some of the nitty-gritty of the science, then you might be interested in listening to our other podcast. Michelle, you want to tell them about our other podcast?

Dr. Tarbox: Our other podcast is called "Dermasphere." It is the podcast by dermatologists for dermatologists. In this podcast, we go over a lot of different articles that are being published about the current state of treatment of dermatologic diseases and how to help better take care of our patients.

So that is more aimed at people who are practicing dermatologists or dermatologically curious. They are longer episodes and they're a little bit more in-depth, but if you are a very curious person, you might also enjoy it.

Dr. Johnson:

Thanks a lot for hanging out with us today, guys, and we will see you next time.