How UV Causes Cancer and Aging

Recently, I made a video about what the world looks like in the ultraviolet. Some things look the same, but generally, it's hazier. Sometimes light and dark are flipped, skin looks blotchier, and fake teeth stand out.

Whoa! Smile for me. Oh my goodness, are my teeth black? Do you have a fake tooth, baby?
-- Yes.
-- Which one?

But the idea for this video started a long time ago with a question I had, which is: How does non-ionizing radiation, like ultraviolet light, damage skin and lead to cancer? I do like to tell people that if you want to see how good your skin could look, look at your butt. Because that's an area that doesn't get sun, and even old people have perfect butts. It's how your skin would age without the sun.

When I thought about what UV light must be doing to our cells and our DNA, I imagined it would be getting in there and breaking all these bonds, and that would be the problem. But in fact, it's kinda the opposite. UV actually facilitates the formation of covalent bonds in our DNA that shouldn't be there. It comes in and it kind of creates these unauthorized bonds between the bases called pyrimidine dimers. Instead of having them bonded across, it bonds the ones next to each other, if that makes sense.
-- Oh.
-- Yeah.

So what happens is two thymines, which are side by side, can actually get covalently bonded together, and that creates a lesion on the DNA. You can think of it like a little bump that makes the DNA hard to read and work with. That's not enough in itself to cause skin cancer. If that were the case, we would just be covered in skin cancers. Then the next step is that we have to repair it, and in the repair, that's when you form mutations that could eventually lead to cancer through a bunch of different pathways. There's actually people who have specific genetic issues that they can't repair these issues, and they are covered in skin cancer.

UV has other effects on the body, like suppressing the immune system. So, as Haley says, it's a "double whammy." There's also kind of a double whammy because UV not only induces these unauthorized bonds; it actually tamps down our natural immune system. One of the best ways we fight cancer is through our immune system. We have constant surveillance through our skin. So not only is sunlight creating these problems, it's actually reducing our ability to fix them. So unfair.

UV light also causes us to visibly age. It's called photo-aging. I should clear up a misconception here that I had, which was: I thought glass blocks all ultraviolet light. So I thought if you're inside a car, for example, you really don't need to put on sunscreen because you're not being exposed to UV light. The car does not block UVA; it's glass. It does block most UVB, but you're still susceptible to those sunspots and those wrinkles through the glass. A lot of my patients, if you look and you compare their hands, the left is more wrinkled or has more sunspots on it because they're driving. So they're sticking that hand...
-- Sticking that hand out their truckers.
Absolutely; you can see it the worst.

And there's a really famous picture of someone whose left side of their face is significantly more, as we'll call it, photo-aged or old-looking than the other side of their face. So that's mostly UVA. And UVA, as I said, it's a longer wavelength, penetrates a little bit deeper. So wrinkles mostly come from the destruction of our collagen and elastin, which are natural fibers that hold up the scaffolding of our skin.

So with age, the cells that secrete collagen, they're called fibroblasts, stop producing as much. What the Sun does is it breaks down the existing collagen and elastin we have. Fibroblasts really like to be stretched; they like to be pulled, and collagen does that. That collagen matrix. So the Sun damages the collagen fibers, leading to less stretch on fibroblasts and less production of collagen, which means that you look a little more saggy.

I know it's very depressing. So sun protection helps the degradation of those collagen and elastin fibers. You know there are a lot of creams on the market that claim to be anti-aging, but the one that really works is sunscreen. Preventing ultraviolet light from hitting your skin is the best thing you can do to avoid skin cancer and to avoid photo-aging. So yeah. It's good advice. Use sunscreen.

Hey, I'm on set for Jurassic World: Fallen Kingdom, and I'm here filming Sci-Fi Test Lab, where we try to recreate some dinosaur parts out of machinery and test them out. So if you want to see that, then click here!