Hey everybody, welcome back to explainment from five. The podcast where we take the questions you always wanted to ask and talk about them in a way that's easy to understand. We are your hosts, I'm Tim. Hi everyone, I'm Kevin.
So Kevin, today we're talking about UV and sunscreen. And why don't we start with this question. How does UV light sanitize surfaces and does it really clean? Yes, Tim.
Yes, it does actually. So, UV light or ultraviolet light, what's special about it is that it's basically it's short enough wavelength that it could penetrate the wickly into cells and viruses. And when it does that, it causes damage basically to the pathogen's DNA. And even though we discovered UV all the way back in 1801 over 200 years ago, it was only in 1960 when the effect of ultraviolet radiation on DNA specifically was established.
So it's used in cleaning because it's a great non-invasive way of basically disinfecting services that doesn't require any toxic or damaging chemicals. And what happens is that the UV light, it ionizes the DNA in those cells and it breaks it down, disrupting any cell functions and eventually killing that bacteria. It also tends to create small amounts of ozone which can do serious damage to cells as well. So one way of ELI-5 explaining it is to say that UV gives pathogens kind of a supercharged cancer.
It damages the bacterial of the viral DNA so badly that the cell can't replicate and then it dies. Which is why most UV sterilization protocols are a minimum of something like 15 minutes, sometimes up to an hour to make sure enough damage is done. I like that way of explaining it and it leads to the second question which I have, which is if UV rays then do cause cancer and UV rays from the sun are dangerous for us. When we use sunscreen, why even bother with some of the weaker SPF products?
Why don't I just go for the strongest stuff out there? Oh right, right. So you know, different strengths are developed because actually different skin tones require different levels of protection. So the skin produces something called melanin that is basically our own natural sunscreen.
And the more melanin you produce, the darker your skin is. So when UV light is detected, it triggers melanin production which actually can give you a tan. If you want that, then you use kind of a lower strength sunscreen that lets basically enough UV natural UV to trigger the melanin production. If you don't want that, then you might want to use a stronger sunscreen.
So high SPF sunscreen is for those with very fair skin that don't produce much melanin leaving them highly susceptible to sunburns. Now SPF 15 is the lowest to be considered sunscreen and that blocks 93% of UV light. The skin is capable of naturally stopping a little UV light. So that is sufficient to get the job done, maybe give you a little tan.
So actually come to think about it. We should probably explain what does SPF even mean? I mean, when you say 15 in SPF 15, what does that number represent and what does it stand for? Oh yeah, good question, good question.
SPF literally stands for the sun protection factor, which was introduced in 1974. It is a measure of the fraction of sunburn producing UV rays that reach the skin. So for example, SPF 15 means that one-fifteenth of the burning radiation will actually reach the skin with the same amount of sunscreen applied. The inverse relationship actually has a really, really interesting marketing effect.
So if you try flipping the equation around like this, SPF 10 stops 90% of UV rays getting to your skin, while SPF 20 stops 95%, SPF 30 stops 97%, SPF 50 stops 98%, and then you have SPF 100, it stops 99%. It is very powerful looking at it that way. Yes, yes. So don't go thinking SPF 100 is something like five times as effective as SPF 20, when all you really do is go from that 95% protection to 99% protection.
So more fundamentally, how does sunscreen stop your skin from getting burned? So sunscreens work in one of two ways. The first is by filtering or even completely blocking the UV rays. Molecules that absorb UV light are able to release the captured energy as heat.
And a second way is by reflecting the UV rays. So they aren't able to reach your skin at all, something achieved by using zinc oxide or titanium oxide. I remember we did an episode on vitamin D, something along the lines of why does the sun provide vitamin D and how is it possible for UV light to produce a vitamin? Oh, yeah, yeah.
I remember that one. It's not really a vitamin, it was one conclusion. And in a nutshell, there is a form of cholesterol present on your skin. So imagine this as sort of like a chunk of frozen vitamin D.
And sunlight curltains ultraviolet B energy, UVB, and is able to convert that cholesterol into vitamin D3, then the D3 goes to your liver, then your kidneys become active, vitamin D. If you want to know more about all that, please go and search up the ELI5 vitamin D episode. If our bodies are constantly losing and then regrowing skin cells, why does this cause long term skin damage? Oh, well, because we're only losing and regrowing that outermost layer of skin.
And near UV radiation can penetrate to the innermost layer of skin, where cells are still alive, and well and fiercely producing more skin to try to keep up with the loss. So if a single UV photon hit one of these cells in the wrong spot as preparing to split, which is, you know, how more cells are produced, this can cause it actually to start misbehaving and be the start of some kind of cancer. Of course, the UV photon has to kind of hit exactly the right spot, exactly the right time to cause that cancer. If this cell is not a regular skin cell, but maybe a pigmentation cell, it's actually even worse since those are able to metastasize even without any unintended mutation.
So finally, wasn't there some issue with a couple of sunscreens recently that led to an industry recall? Oh, yeah. Yeah, there was a recall of five copper-tone aerosol sunscreen spray products manufactured between the dates of January 10, 2021 and June 15, 2021 to the consumer level. They identified the presence of benzene in these products.
That chemical benzene is a carcinogen of human that has been linked to certain blood disorders and cancers, with copper-tone basically explaining that while they contain benzene, the levels of this chemical aren't likely high enough to cause health problems, but it was still a recall. Well, that's good to know. And I'm sure there's a list out there on the web where you can check if any products you've used have been linked to that. Did you learn something new?
If you did, send us an email. We'll see you all next week.