Why do I tan more in the US?

14:12Neelam Vashi: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.

14:22Julian Groebner: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.

14:40Neelam Vashi: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's considered South India. So much closer to the tropics.

14:54Julian Groebner: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. So only from that point of view, you would expect more UV radiation in India than in Boston.

15:16Neelam Vashi: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?

15:39Julian Groebner: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.

16:42Neelam Vashi:Perfect.

16:43Julian Groebner: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.

17:05Neelam Vashi: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.

17:50Neelam Vashi: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.

18:13Namrata: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.

18:28Neelam Vashi:And what do you think about getting a tan?

18:32Namrata: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.

18:43Neelam Vashi:And getting too tanned is not desirable because?

18:49Namrata: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.

18:59Neelam Vashi:UV radiation in Mumbai is a bit lower than it is for the 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.

19:21Chhavi Sachdev: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.

19:35Neelam Vashi: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.

19:50Chhavi Sachdev: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.

20:19Neelam Vashi: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.

20:56Neelam Vashi: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?

21:12Julian Groebner:From a physical point of view, water or water molecules are not absorbing UV radiation.

21:21Neelam Vashi:This is Julian Grobner again from the World Radiation Center.

21:24Julian Groebner: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.

21:36Neelam Vashi: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 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-made, like industrial emissions and debris from construction sites.

22:19Julian Groebner: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.

22:44Neelam Vashi: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?

23:01Julian Groebner: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.

23:52Wow.

23:52Julian Groebner: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.

24:02Neelam Vashi: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?

24:22Chhavi Sachdev: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.

25:01Neelam Vashi: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 Center agrees that the difference in Namrata's experience could be about a change in behavior.

25:50Julian Groebner: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 lunch. And then in the summer, the radiation will actually be quite strong because also in Boston, the sun will be nearly overhead. 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.

26:40Julian Groebner:So, you know, it's a lot about behavior as well.

26:43Neelam Vashi: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.

27:18Julian Groebner:That could be an explanation.

27:22Neelam Vashi: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, Namrita.

28:02Neelam Vashi:Just keep reapplying your sunscreen. Now over to you for the credits.

28:07Namrata:That's it for this episode of CrowdScience from the BBC World Service. The question was from me, Namrita, in Hyderabad. This show was presented by Chavi Sajdev and produced by Yoke Langville. 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.

28:34Julian Groebner:When you hear the phrase made in China, what do you think? I'm Tristan Redman.

28:39Chhavi Sachdev:And I'm Asma Khalid. And together we host the Global Story podcast from the BBC. And today on our show, we look at the origins and evolution of made in China, because it actually wasn't inevitable. What we're talking about is the world's largest communist nation is at the beating heart of the capitalist system.

28:58Julian Groebner:For more, listen to The Global Story on BBC.com or wherever you get your podcasts.