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I'm Chavi Sajtev and I'm at the beach in Mumbai, finding out what people think about tanning, because that's what we're looking at this week, all thanks to a question from a listener, of course. Hi, I'm Namrata and I work in Boston, but currently I'm visiting India. So I'm in Hyderabad right now. My question for CrowdScience is, I'm an Indian who's been living in the U.S. for the past three years. And I've noticed that I tan more in the summers there than I would in India. Is it my imagination or is there anything more to this? Namrata is convinced that she gets more of a tan in Boston in the USA. than she does in India, and she wants to know what's going on. It is odd because it seems like the reverse of what you'd expect to happen. India is closer to the equator. The sun is stronger. We have longer summers. So it seems reasonable that she'd get a deeper tan back home. But she first noticed that she was tanning more when she went out running in Boston. So in 2024, I was on a run at about 9, 9.30 in the morning in Boston. The temperatures would have been in late 20s, probably somewhere around 27 is what I remember. Weak memory, but that's what I remember. 27 Celsius, just to be clear. 27 Celsius, yes, 27 Celsius. Okay, so very pleasant for Bostonians. Pretty pleasant weather, pretty pleasant temperature. And I went for a run and I came back to see my leg, the half of my leg, my arm completely dark. Like it was really, really dark. And I felt, OK, this is tanning, but this is different tanning. And since then, I've constantly observed it. And I remember this not happening as quickly in India as it happens in Boston. You know, we've had a similar trajectory because I used to also live in Boston. When I lived in Boston, I used to be really arrogant about the melanin in my skin and really confident that I couldn't burn until one day I did. Is there anything you do differently in the US that could explain the difference? Not really. I have been wearing more sunscreen than compared to India in the past four or five years. I've learned to wear sunscreen. I walk around more in the summers there in the US than in India. Because again, what we consider summer in India is like extreme heat compared to what summer is in the US. What about environmentally? Do you think there is something going on with geography or climate that could explain it? So the other thing I do observe, so in the US is the angle of the sun, right, that hits you. I feel that's definitely different. In noon in India, you would have sun almost perpendicular to the earth. Whereas in Boston, even in the summers, it's never perpendicular. So it always feels a little different. The other thing I feel personally is Boston, despite being a coastal city, is slightly drier most of the year. Yeah, we'll definitely try to unpackage that and talk to some experts about what happens with the angle of the sun is going through drier air and hitting our skin. Is there anything else you've thought of that could be contributing to this? Yes, I had read an article about pollution in a magazine recently, and they said that India should be actually more hot than it is right now. But it's because the pollution that's there in the air, which is actually reducing the amount of sun rays that hit the ground and increase the heat of the country or the roads or whatever. and the air in Boston is compared to way, way cleaner. So I wonder if all these factors are affecting how the radiation is interacting with our skin. Namrata has quite a few suggestions about why she thinks she tans more in Boston than back home in India. Pollution, climate, the angle of the sun. And I'm particularly keen to find out the answer to this question because the same thing happened to me. But let's start with the basics. What makes our skin tan and burn? When we're talking about sun damage, we're talking about ultraviolet UV radiation. Neelam Vashi is a dermatologist who's actually based in Boston, where our listener Namrtha now lives. UV radiation, ultraviolet radiation, is part of the electromagnetic spectrum, from x-rays to infrared radiation and microwaves. So there's different types of UV radiation. There's UVA and there's UVB. It's important to understand the difference because they actually behave quite differently. There's a third type of UV radiation, too, known as UVC, which is the most harmful. But that doesn't actually reach the Earth's surface as it's absorbed by the atmosphere. So UVB rays are what is associated with sunburn, so B for burn. They affect the top layers of the skin and are strongest in the middle of the day and also during the summer months. UVB will damage the skin directly and that what will trigger this pain redness and peeling and that our sunburn response Now over time UVB exposure will also increase the risk of skin cancers So it UVB that was responsible for my painful experience of burning when I was living in Boston UVB is also the rays that help produce vitamin D, so beneficial in small amounts. UVA goes deeper into the skin, so it is responsible for that long-term skin damage. And so what we think of that, skin wrinkles and dark spots. Now, I'd always thought the darker color of my skin was my superpower when it comes to being protected from the sun. And that's because of melanin. So melanin, what is that? It's the pigment that gives our skin its color. So what melanin does, it absorbs and scatters UV light, UV radiation from the sun that's helping protects skin cells from DNA damage. Melanin is housed in cells called melanocytes. We all have the same number of melanocytes, but varying levels of melanin. And there are different types of melanin. It's eumelanin, so E-U melanin, and then pheomelanin, P-H-E-O melanin. And the balance of these two actually plays a big role in how our skin responds and the color of our skin. Brown people have more eumelanin. So eumelanin is that dark brown to black pigment. It's the type of melanin that provides the strongest protection against UV radiation. So it absorbs UV rays more efficiently and helps to neutralize that harmful energy before it can damage the skin. Pheumelanin, meanwhile, is a red-yellow pigment, and it's more common in people with fair skin, freckles, red or blonde hair, and lighter eye colors. Everyone has some amount of pheomelanin. Namrata and I have an advantage. We're less likely to burn because of the type of melanin we have, eumelanin, and how it's distributed. But that didn't protect either of us when we were in the US. I wanted to head out and see if I could find anyone who'd had an experience like ours in India. It's a pretty hazy winter morning in Mumbai. I'm on a beach where I can see across the bay the buildings are silhouetted in smog. In the water are some egrets, a flock of seagulls gently rocking on the waves. I wanted to ask some of the people who are here for exercise how they feel about getting a suntan and being exposed to the sun. So I'm with long-distance runner and endurance athlete Shibani Gharat to ask her her experience. So I used to run earlier in the day, but then, you know, given my job and I reach home pretty late every day, so I start running late, you know, in the morning these days. I started about 7.30, quarter to 8 kind of a thing. So our listener grew up in India and she now lives in Boston. And she's noticed that her skin tans much more when she's out on a run in Boston. And we're trying to find out why. Have you ever been running in the US? Quite a bit. In fact, you know, I don't know about, you know, areas like Boston. But I was in Hawaii in September. and I realized that I am looking browner while running in the sun around the same time that I would run in Mumbai as compared to you know when I ran over here I was browner there but maybe it's because of the clearer skies I feel and the skies here are not clear no they are very polluted because of all the construction work going on in the city. So maybe because of that. Hawaii is in the tropics, so you might expect to get quite a tan there. But both Shibani and our listener Namrata think the difference in their experience when they're outdoors in the sun in the US might be to do with the climate and pollution. Could they be right? That's what we're finding out next. Starting a business can be overwhelming. You're juggling multiple roles, designer, marketer, logistics manager, all while bringing your vision to life. Shopify helps millions of business sell online. Build fast with templates and AI descriptions and photos, inventory and shipping. Sign up for your one euro per month trial and start selling today at shopify.nl. That's shopify.nl. It's time to see what you can accomplish with Shopify by your side. Bingo. BBCNL, the place for the best British misdaad series. Just on your Netherlands TV. makes our skin tan. But is there actually a difference in the level of UV radiation in India and the US? Namrta was visiting Hyderabad in the south when we talked to her, but she grew up in Nashik in northwest India and later studied in Bangalore, which is also in the south. India is a huge country and it might be worth factoring in the locations where she spent time too. I'm Julian Gröbner. I'm working in Switzerland in an institute that is called the World Radiation Center. And we are responsible for the calibration of radiation instruments all over the world. Julian is a physicist. The instruments he's talking about measure different types of radiation in the environment, including solar radiation and ultraviolet or UV radiation. If we focus on UV radiation, then what dominates the amount of UV radiation that reaches the Earth's surface is essentially the atmospheric transmission, which is crucially dependent for the UV radiation component on the ozone amount. Ozone is a gas made up of oxygen atoms in the stratosphere. It acts like a shield, reducing the amount of harmful UV radiation that reaches the Earth. Ozone is an important variable for UV radiation. And so taking Boston and India as an example. So Boston is a northern middle latitude location. And India is much closer to the equator And Nasik where Namrata spent a portion of her life is very much tropical And then Bangalore the other city that she was in is also you know it considered South India so much closer to the tropics. Exactly. And so I checked the amounts of ozone that you would expect at these locations. And the amount of ozone in India at these locations, it's much, much less than what you would find in Boston. Aha. So only from that point of view, you would expect more UV radiation in India than in Boston. So Julian's actually checked the ozone levels for CrowdScience in the cities where our listener Namratha lived, and they turn out to be much lower than the level in Boston. Lower levels of ozone mean UV radiation is higher. So you'd actually expect Namratha to tan more back home. India is also nearer the equator. Does the fact that we're slightly closer to the sun make a difference? So the distance, that's not relevant. But the elevation of the sun over the horizon, so the closer the sun is to overhead, to the zenith, makes the rays go through the atmosphere, let's say, on a more direct path. So the radiation will be less absorbed. and so there will be more. And so clearly in India where the sun is overall over the whole year always much closer to the zenith than in other locations like in Boston, you would also have a significant increase of the radiation. And so I took out some data from some websites, from a satellite And if we just consider ozone and that position of the sun in the sky, then what is interesting is that I took Bangalore and Boston as an example. Perfect. And the maximum UV radiation in Boston is barely as much as the minimum amount of UV radiation you would find throughout the year in Bangalore. So in Bangalore, every day of the year, you will have at least the maximum amount of UV radiation you would find in Boston. That's incredible. So you would imagine somebody who's out in the sun in Bangalore would tan more than somebody who's in Boston. From that point of view, yes. All the evidence Julian has looked up for crowd science, the ozone levels where Namrata grew up and lived in India, the ozone level in Boston, and the position of the sun in India point to the same conclusion. UV levels in India are higher. So we're no closer to answering why Namrata finds that she tans more in the US than in India. I'm heading out again to find out about the local experience of tanning in India from people who spend a lot of time outside. So I'm now talking to golfers in Mumbai who spend many hours outside exposed to the sun when they're playing. Mumbai doesn't have any public golf courses, it's quite a privileged pursuit, so I'm at a private club. It's another hazy day and although the city and traffic continue to bustle outside here, it's relatively serene and so verdant. Hi, I'm Veer Puri. I play golf. I like to hike a lot. I like to do a bunch of other outdoor activities when I get the time to. So yeah, I'm pretty much exposed to the sun most of the time, especially living in Bombay. And what do you think about getting a tan? I personally enjoy a light tan but it could get dark if you expose yourself to the sun too much so I try not to as much as I can And getting too tanned is not desirable because? I don't know, I just don't like the look on myself Yeah, it's just too much of a contrast to what I actually look like UV radiation in Mumbai is a bit lower than it is further south in Bangalore, where our listener Namrata lived. But it's still much higher than Boston in the summer, and you are likely to get a tan if you're out for long periods and don't cover up. Veer protects himself from the sun, and he doesn't like getting a dark tan, which is something a lot of Indians feel strongly about. In places like India and actually other countries as well, lighter skin has historically been associated with beauty, success and social advantage. And so this concept is known as colorism. That's Neelam Vashi, the dermatologist in Boston we heard from earlier. Colorism, sometimes also called shadism, is the term for a prejudice that's based on skin tone. And here in India, it is rather widespread. The preference has very deep roots. It's shaped by history, colonial influence, caste dynamics, media representations, and then decades of advertising. Because of this, many people grow up with this idea that tanning is undesirable, not just cosmetically, but also socially. So when tanning is framed negatively from a young age, they notice it more. And it's interpreted as something unusual or concerning. So our approach to tanning is cultural and maybe even psychological. I know as a child, I had a lack of playmates because so many kids weren't allowed out in the sun by their mums for fear of getting dark or tanned. Our listener Namrata didn't raise tanning as an issue in terms of skin color. But if we've grown up in India feeling that tanning is undesirable, then we might notice it and even feel concerned about it when we spend more time out in the sun in a northern middle latitude city like Boston. We've already discovered that we'd expect the level of UV radiation to be higher in India than in Boston. But Namrata was convinced that she tans more when she's in the U.S. She also had some other ideas about what could explain the difference she's experienced. First, the climate. Boston is drier and India is a lot more humid. Could that be an answer? From a physical point of view, water or water molecules are not absorbing UV radiation. This is Julian Grobner again from the World Radiation Center. A very clean ocean or a very clean lake, radiation will be able to penetrate quite deep into the water. And so the same will happen, of course, in the atmosphere. year. That hypothesis is out. Humidity offers no protection against UV radiation, so the drier climate in Boston isn't a factor. What about Namrata's other suggestion, that pollution is the reason for the difference? India is significantly more polluted than the United States. Sometimes you can see it like a smog or a haze. Sometimes it's not so obvious. But even our small All towns are known for dangerously poor air quality which is directly affected by particles in the air called aerosols These aerosols can be natural such as wildfire smoke or volcanic ash or man like industrial emissions and debris from construction sites Aerosols in the atmosphere will also scatter and absorb radiation. So I looked up several stations that are measuring the amount of aerosols and consistently in all the stations I checked in India, the amount of aerosols are significantly higher than in other regions of the world. I'm shaking my head here. Nobody can compete with us. So Julian, from what we've talked about, is pollution in India then the most likely reason that you would not get as tanned in India as you would in a city like Boston in America? It is the only variable that I could find that would decrease the amount of UV radiation in India compared to Boston, because everything else would go the other way. You know, there's much less ozone in India than in Boston. So that would mean more irradiation in India. The sun is much higher in the sky in India. So all of these components would lead to saying UV radiation is higher in India than in Boston. And so only the pollution is the only parameter that will reduce the amount of radiation in India compared to Boston. And it would bring it, I checked, I did some calculations, it could possibly bring it to about the same level. Wow. But it would never be able to decrease it to less than what you have in Boston. That would just not be possible. Okay, good to know. Thank you for doing that. The evidence still suggests that you'd expect to get more of a tan in India than in Boston. So what's the answer to Namrata's experience? How come she's getting more tan in Boston when UV radiation, which is what gives us a tan, is higher in India? I think it could be behavioral. So, you know, she's spending more time outside. Neelam Vashi, the dermatologist from Boston. Not reapplying the sunscreen. So it's not just about that first application, but it's also about using it properly, reapplying, using a broad spectrum. So, yeah, again, many people, they apply the sunscreen once in the morning and then they assume they're protected for the whole day. They have that six-hour protection, but it does wear off and especially wears off faster if, you know, one is exercising like the collar is and there's a sweating component to it as well. Remember, our listener Namratha told us that she spends more time outside in Boston. From experience, I can say that in Boston, I actively wanted to feel the sun on my skin because I was cold all the time. My office took air conditioning very seriously. I can't ever remember feeling hot there. Perhaps because it's less humid and the breeze is usually cool, I just didn't notice the exposure like I would in India where hot is hot. Most people I know in India consciously avoid going out in the midday sun or they cover up to avoid the heat if they have to. It really isn't pleasant. Julian Grobner from the World Radiation Centre agrees that the difference in Namrata's experience could be about a change in behavior. If maybe, just as an example, if in India it is very hot and humid, you might stay indoors during the hot hours of the day, and then you go out in the mornings or in the afternoons, and then UV radiation will already be much less, even in the tropics, because the sun will be lower in the sky. and in contrast in boston you might actually be a bit chilly and so you actually say oh i'm going out over over lunch and then in the summer the radiation will actually be quite strong because also in boston the sun will be nearly nearly overhead yeah and so there then the uv radiation will practically speaking be higher than what you would experience in india going out in let's say the late afternoon. So, you know, it's a lot about behavior as well. That's really interesting. So I also lived in Boston for a long time in my 20s. And it's funny because I am mirroring exactly the behaviors you are saying. So here, if I have to work out outdoors, I go for a walk, I don't run, I have no knees for running. I go either in the morning or in the evening. And in Boston, I literally would go for a walk in my lunch hour because that was the nicest part of the day. So you see, that could be an explanation, you know. That could be an explanation. So we have an answer for you, Namruta, but it's probably not what you were expecting. It's not what I was expecting either, but we put your very convincing theories to the test and it turns out that it's actually down to behavior and possibly perception. Even with the pollution in India, UV radiation is never going to be higher in Boston. It's more likely to be about the time of day you're going out for a run and how much protection you have from the sun. Plus, there could be a cultural or even psychological element in how we respond to changes in our skin when we're away from India. I do hope none of this will put you off running in Boston, Namrata. Just keep reapplying your sunscreen. Now over to you for the credits. That's it for this episode of Crowd Science from the BBC World Service. The question was from me, Namrita, in Hyderabad. This show was presented by Chavi Sajdev and produced by Yoke Lanville. If you have a question on any science subject and you want the team to investigate, why not email crowdscience at bbc.co.uk. Goodbye. Starting a business can be overwhelming. You're juggling multiple roles, designer, marketer, logistics manager, all while bringing your vision to life. Shopify helps millions of business sell online. Build fast with templates and AI descriptions and photos, inventory and shipping. Sign up for your one euro per month trial and start selling today at shopify.nl. That's shopify.nl. It's time to see what you can accomplish with Shopify by your side. murder, mystery and an accent where you immediately fall. I'm your service, ma'am. On BBCNL you'll find the best British misdaad series. 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