10/02/2020

Ask An Expert: Why Do We Itch?

17:22 minutes

a brown bear in the water raising one of its fore paws to scratch its head
We’ve all had that urge to scratch an itch. But why do we do it? Credit: Tambako/Flickr/CC BY-ND 2.0

The pandemic has us feeling a lot of things: anxious, stressed, tired. But what about itchy? 

Have you ever had a hard time not scratching or rubbing your face in public? Or had an unreachable itch beneath a mask? This week on Science Friday, we ask an expert: why do we itch? And is there any relief to be found in understanding the neuroscience behind why we scratch? 

Ira asks these questions and more to Diana Bautista, professor of molecular and cellular biology at the University of California Berkeley. They were joined by a live Zoom audience, who were also itching to ask their own questions. Watch the conversation below to get an explanation on all things itch!

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Segment Guests

Diana Bautista

Diana Bautista is a professor in the Department of Molecular and Cellular Biology at the University of California, Berkeley in Berkeley, California.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. The pandemic has us feeling a lot of things, but what about itchy? Now here’s a situation that has happened to me recently. I headed into the drugstore so I put on my mask, I went inside. But pretty soon my face started to it’s right between my nose and my cheek about right there, right under my mask.

So what was I supposed to do? I didn’t want to touch my face or take off my mask to scratch it. That would kind of defeat the point of wearing one, right? It’s so difficult to resist that itchy feeling. But I suffered through it till I could get back into my car and safely scratch. The things we do to keep ourselves and others safe, right?

Well, how many times has this happened to you over the last several months? And wouldn’t it be nice if we could just suppress that itchy feeling? Maybe there’s something we could learn from neuroscience to keep us from pulling off our masks to scratch that itch. Well, we’re going to talk to an expert here to help explain the science behind our itchy pandemic experiences. And to answer all things itch is our expert, Dr. Diana Bautista, Professor in the Department of Molecular and Cellular Biology, University of California at Berkeley. Welcome to Science Friday.

DIANA BAUTISTA: Thank you. I’m excited to be here.

IRA FLATOW: And we want everyone listening to know this interview is being recorded in front of a live Zoom audience because, well, we miss having you being a part of our show. So this is our way of bringing you into our conversation. And if you didn’t get to join us this time, don’t worry about it. Keep an eye out for announcements of future Zoom tapings so you can participate in our social media or on our website at ScienceFriday.com/events. Let’s begin. Dr. Bautista, can you relate to the itchy encounter I had? I’m sure it’s happened to you, right?

DIANA BAUTISTA: Oh it happens to me many times a day. We are by nature, very itchy animals, human beings. And even just the mention of the word itch, I have to apologize to everyone, you’re going to be scratching a lot during this interview. And the idea that you can’t touch your face, which we’re being told all the time these days due to COVID is just enough to make you obsess and think about it constantly.

IRA FLATOW: You know I’ve always wondered why is it that there are some things that make you itch when they touch your body. Maybe it’s wool, something like that. And then you have cloth, something that does not make you itch. Do we know why that is?

DIANA BAUTISTA: We know that it varies a lot from person to person. Some people love cashmere and other people find it incredibly itchy. And that touch evoked itch is also known as mechanical itch. And it actually represents one of the great mysteries in biology. We don’t really understand how something like a gentle touch could be innocuous in some cases and really itchy in another.

IRA FLATOW: Is there a relationship between itch and pain? I’ve heard before that those systems are connected in some way.

DIANA BAUTISTA: Yeah, there is a very intimate interaction between our itch neurons and our pain neurons and how we experience these sensations. And for a long time, it was thought that itch is a subset of pain or a mild pain. But now we know that it’s its own sensation and there are unique free nerve endings in our skin that mediate itch sensations and send signals from your skin to your brain to trigger that sensation of itch, to trigger that negative emotion you have to an itchy sensation and to drive scratching.

IRA FLATOW: When you say that there are signals sent to our brain, is there in each center in my brain someplace?

DIANA BAUTISTA: Definitely, when you experience itch there are several regions of the brain that become activated. Our cortical regions that help you identify where that itch is located, you activate the motor system to trigger scratching behaviors, and then there’s the emotional component as well.

IRA FLATOW: Wow, so if I scratch are their endorphins, sort of pleasure things released in our brain at the same time saying, oh, that feels good.

DIANA BAUTISTA: Yeah. Scratching is quite complex and interesting to neuroscientists because scratching helps you and makes you feel better in many ways. There’s a very local effect of scratching, where applying scratching or any type of pain, like hot, really hot water or icy, an icy compress, anything that causes pain can literally block that itch signal from reaching the brain or decrease the intensity of the itch sensation. So you get this sort of immediate relief from that scratching.

But there’s a secondary effect. When you scratch, brain regions that are associated with reward and also addiction release dopamine and serotonin gets released and you get this big reward from scratching as well. And that can lead to a really horrible itch-scratch cycle where it’s very hard to stop. And probably people have done this when they’ve scratched their itchy mosquito bite until it bleeds. That’s because of that reward.

IRA FLATOW: We have our first Zoom question from Shiro Tanaka, who says, how is the itchy sensation defined dermatologically? Is it an inflammation?

DIANA BAUTISTA: Yes, so acute itch is very different from chronic itch. An acute itch, you activate these itch specific neurons that send an electrical signal to the brain to trigger the sensation and then to trigger scratching behaviors. And it’s very short term. With something like a mosquito bite that’s a little bit longer, your nervous system actually releases compounds and regulates the vasculature to allow immune cells to come in. And that’s really important in the case of, for example, insects that could burrow into your skin that carry disease vectors or parasitic worms. And that immune system comes in. The scratching removes the insect. The immune system gets rid of infected cells. But then the system goes crazy under chronic itch conditions.

IRA FLATOW: Tell me when a chronic itch condition is.

DIANA BAUTISTA: Yeah chronic itch refers to a variety of different disorders and dysfunctions that lead to itch that really can’t be treated by antihistamines and there are very poor therapeutics. And it’s itch that is really long term. So if you imagine the worst itch you ever experienced, and imagined what your life would be like if that itch were to spread over extended parts of your body and were present for every second of every day. And chronic itch has a decreased quality of life similar to the very worst chronic pain conditions.

IRA FLATOW: Are there treatments for these kinds of things?

DIANA BAUTISTA: There are a lot of clinical trials going on right now due to the big boom in itch research over the last five years but right now corticosteroids are often the first line that are prescribed. But they’re really not super effective. And even antihistamines for some forms of allergic itch don’t really work so there’s a big therapeutic need out there.

IRA FLATOW: I remember doctors used to tell kids start to scratch their chickenpox. I mean it’s sort of counterintuitive to your own mind. But it’s bad for you.

DIANA BAUTISTA: Yeah I think short term, acute itch serves as an important warning system, right? We feel itchy when we get a mosquito bite. Mosquitoes carry malaria. Learning to associate that itch with a mosquito helps you develop protective behaviors like putting on DEET or going into the tent when you’re camping when you’re surrounded by mosquitoes or scratching, swatting away. And those are good things.

But under chronic itch conditions, the constant scratching causes damage to the skin and makes the itch worse. And so it’s really counterintuitive. But anybody who’s had a kid who has had eczema knows it’s really hard to not scratch that chronic itch. And it’s called this really vicious itch-scratch cycle that’s really difficult to stop.

IRA FLATOW: That’s a good segue to our next listener, Lisa Hale, has a question about mosquito bites. Hi, go ahead.

LISA HALE: Hi. I was wondering, are some people are more allergic? If they are, do they tend to itch more than like say someone who isn’t?

DIANA BAUTISTA: Yes, so there’s a lot of variation. Some people don’t have an allergic reaction at all or notice when they have mosquito bites. Other people are unfortunate like myself, who suffered from eczema as a kid. And now I’m super sensitive to bug bites and noseeums and mosquitoes. And I have a very large allergic reaction that occurs. And the itch can persist for several days. So there’s a great variation depending on who you are and what your biology is.

IRA FLATOW: Let’s go back to my drugstore visit for a second. It was so hard to fight the urge to scratch, I almost couldn’t do it. Are there any tricks to overriding these? Can you think about something, you know, whatever, because I always wondered one of the things I’ve always wondered about why I could never be an astronaut besides a lot of other reasons, is that if I had the helmet in the spacesuit on and I had to scratch my nose or whatever, that would drive me crazy.

DIANA BAUTISTA: Yes, it definitely drives me crazy. And so when I go to the pharmacy or go grocery shopping, I do have a period in my car where I sit there and I touch my face and I scratch and then I actively think, because we can suppress that strong desire to scratch through– we have control over our motor system. It’s sometimes hard to exert that control, but we can do it.

And so I scratch, I get it out of my system and I actively think, OK, don’t touch your face. Don’t touch your mask. Don’t scratch. And I think that distraction is a big part of it. And actually children with eczema, one of the most effective therapies to get them to stop scratching is through playing video games, probably educational video games are encouraged to get their minds off of their itchiness. And that’s what I suggest you do at the pharmacy.

IRA FLATOW: So you pre-scratch yourself.

DIANA BAUTISTA: I do.

IRA FLATOW: You give yourself sort of a pep talk before you go in there and say, I’m going to get it out of my system. Now listen, system, I’m scratching now. I’m getting it out of my system. And it listens.

IRA FLATOW: Yes. Actively fighting that urge. And one thing people don’t realize is how much we touch our face. Our face, because most people primarily use their visual system to navigate the world. We have a lot of enervation, a lot of these free nerve endings in our face that makes it super sensitive, that allows us to be very responsive if a bug lands there or if we get something harmful in our eye. And so we’re super sensitive. And we touch our face hundreds and hundreds of times a day without even realizing it.

IRA FLATOW: I’m doing it now without thinking.

DIANA BAUTISTA: Yeah. Definitely.

IRA FLATOW: Well that brings me to a question I hadn’t thought about until this very moment. And that is why when we touch our faces or scratch your face, it feels like a sensation of scratching but on our soles of our feet, it feels like it’s tickling.

DIANA BAUTISTA: Ah.

IRA FLATOW: I mean have you ever thought about that? Is that a whole different– that’s a whole different subject.

DIANA BAUTISTA: Yeah and it’s a fascinating mystery in sensory biology. We know a lot about the senses, but our sense of touch that spans gentle, pleasant touching to itchiness to tickle to pain, is one of the least understood senses, which is really surprising to most people.

IRA FLATOW: We’re all familiar, of course with the experience of an itchy bug bite that you just can’t find any relief from. And there are other times you scratch an itch and the feeling goes away. Why are we able to satisfy an itch in some cases but not in other cases?

DIANA BAUTISTA: The itch relief you get from that temporary pain of scratching or putting on really hot water on your mosquito bite is very temporary and it’s not complete. So you get partial relief, but it’s really not enough. When you have chronic itch, that is really constant and the neurons that innervate the skin, that send these signals become hyperactive, as well as the brain regions that are processing these signals. The system becomes primed so that it’s very difficult to turn off.

And scratching as hard as you can, which normally would hurt, if you scratch an area of your body that doesn’t have that itch, is not providing relief. But you’re still triggering some of those reward centers without getting the actual relief of itchy sensations. And that drives this constant damage to the skin and more itch. And that’s why it’s a cycle that’s really difficult to break.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios. Some people have this talent, I call it a talent. I remember seeing it in the Odd Couple movie, where they’re sitting in the restaurant and one of the characters, can’t remember which one, Felix, starts doing this, [GURGLING NOISE] starts making a noise inside his mouth. And his roommate says, what are you doing? He says, I’m itching the inside of my ear. Do you know what I’m talking about?

DIANA BAUTISTA: I do. I know exactly what you’re talking about. And we do experience itch in the back of our throat. Sometimes if you eat something that you’re allergic to, people with severe allergies especially, you can feel itch inside your ears, in the back of your throat, and inside your nose. And the same types of neurons that innervate our skin that respond to different chemical itch compounds can be triggered actually internally. But little is known about those.

IRA FLATOW: So it’s very embarrassing. I do it. I do it. And when I saw that in the movie, I said, gee, I’m not the only one who does that. Moving on, I’ve seen cats and dogs scratch themselves. We all have. How prevalent is then itchiness in the animal kingdom? Do all animals scratch an itch?

DIANA BAUTISTA: Yeah, I think people don’t realize that itch is really a highly conserved process and scratching across the entire animal kingdom, because it is really an important protective system that we’ve evolved to avoid harm. And it’s not limited to cats and dogs and humans. Even fish can experience a itch type sensation. They get infected by parasites just like we do.

Of course, they can’t scratch themselves. So what they do is they’ll rub against coral to try to get rid of that and get some relief. Or they’ll actually, some fish will go to cleaning stations in the ocean where there are small fish that come in and actually bite them and remove those parasites. Even insects can be infected. So even flies can be infected with mites. And they also have behaviors that look a lot like scratching, where they actually can rub and remove mites from their body.

IRA FLATOW: OK, you certainly do know a lot about itching. But there’s got to be some stuff you still want to know about. What do you still want to know about?

DIANA BAUTISTA: One of the big questions that we’re interested in is understanding mechanical itch? What is it about that itchy sweater that gets you or that itchy mask? We really don’t know. We know a lot more about chemical itch. The other big question that really I think, is shocking that we don’t know more about, our switch is very quick and in some cases click to turn on and long lasting, changes in normal sensitivity. So we for example, when you have chronic itch, a gentle touch that’s normally pleasant or innocuous, becomes itchy.

But if you have chronic pain, that gentle touch becomes painful. How do these normal sensations that we just take for granted really switch and it could be really debilitating, where if you constantly feel the itch from the weight of your clothes or chronic pain from a gentle touch or caress. And we really don’t know how these switches occur and why we’re seeing these chronic conditions at really crazy high rates across the world population. These are normal protective systems that warn us against burning ourself or avoiding toxic plants, that now are just turned on all of the time.

DIANA BAUTISTA: Well, you have driven me to try the Diana Bautista method of talking myself out of scratch– I so want to scratch this part of my shoulder now that you’ve talked about it. But I’m not going to do it. It doesn’t itch. It doesn’t itch. It doesn’t itch. Thank you, Diana. It’s been a great conversation.

DIANA BAUTISTA: Thank you so much.

IRA FLATOW: And I know we have just scratched the surface of this topic. So we’ll come back and talk with you more Dr. Diana Bautista, Professor in the Department of Molecular and Cellular Biology at the University of California at Berkeley. And you can watch the entire video of this interview and sign up to find out about sitting in on a future Zoom interview on our website at ScienceFriday.com/events.

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