(Intro)

It's summer here in the northern hemisphere, and you know what that means -- sunscreen season! You've probably heard this before, but it's worth repeating anyway: exposure to the sun, especially when you get tanned or burned, increases your risk of developing skin cancer, so stop going outside! Well, you can go outside, but wear sunscreen!

But if you do get tanned or sunburned, we will assume by accident, there's a lot going on inside your skin. The Sun is not actually tanning or burning you, the whole process is actually a defense mechanism and you are tanning and burning yourself. The trouble with sunlight is that it contains lots of radiation in the ultraviolet part of the spectrum, and some of that has enough energy to damage the cells in your skin, especially their DNA.

We divide UV radiation into 3 types based on wavelength: UVA, which has a longer wavelength and packs the least energy, UVB in the middle, and UVC, with a shorter wavelength and the most energy. But we don't really need to worry about UVC because it's absorbed by the atmosphere, but UVB can cause enough damage to sunburn and UVA might make you tan. When receptors in special skin cells called melanocytes detect the UVA radiation in sunlight, they start producing extra melanin, a pigment that darkens skin color.

But melanin's real job is to absorb UV radiation before it can damage too many of your skin cells. Basically, when you tan, your body is realizing that more sun exposure might be coming and it tries to protect you. But sometimes, that's not enough. When UVB rays damage a cell's DNA, it'll often destroy itself in a process called apoptosis; if too many cells do this, an immune response kicks in, and that immune response is otherwise knows as a sunburn. Basically, your skin cells are like, "My DNA has been damaged so I must murder myself before I give you cancer!". Blood flow increases to the area to help with healing, which is why sunburns are usually red and warm and after a while all those dead cells can start to peel away. Get enough exposure and so much of your tissue will destroy itself that you might even end up with blisters like in a second degree burn.

Sunscreen helps because it contains substances like benzophenone which absorb or even reflect UV radiation so your trip to the beach doesn't have to involve sacrificing skin cells or increasing your risk of cancer.

Thanks to Patreon patrons Ryan Stirling and the Grants for asking this question and thank you to all of our Patrons, who keep these answers coming and also get them a little bit early. If you'd like to submit a question to be answered, you can go to patreon.com/scishow and don't forget to go to youtube.com/scishow and subscribe.