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Speaker 1: Welcome to brain stuff from how stuff works. Hey, brain stuff,

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Speaker 1: Lauren Volga bomb here when the weather is nice, I've

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Speaker 1: been made to understand that some people enjoy spending time

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Speaker 1: outdoors where they're exposed to, among other things, sunlight. Stuff

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Speaker 1: in sunlight can make stuff in your skin produce more pigment,

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Speaker 1: which shows up as freckles or a tan. But how why?

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Speaker 1: Scientifically speaking, the skin freckling tan both happen in your epidermis,

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Speaker 1: which is the tough, resilient frosting on our body's cake.

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Speaker 1: Under normal circumstances, it protects and helps hold in our precious,

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Speaker 1: squishy insides. Your epidermis contains a few kinds of cells,

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Speaker 1: but the ones were primarily concerned with here are the

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Speaker 1: carrotino sites and the melano sites. Carrotino sites make up

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Speaker 1: most of your epidermis. There are skin cells that are

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Speaker 1: maturing and getting pushed upward towards your skin surface by

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Speaker 1: new cell growth. Melano sites are specialized cells that create

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Speaker 1: pigmented proteins called melanin. And by the way, they're not

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Speaker 1: only found in our skin. Melanocytes are also at work

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Speaker 1: in your eyes and hair, giving them their color, and

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Speaker 1: in your heart inner ear and brain doing. No one

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Speaker 1: is really sure what conspiring to make you enjoy reality

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Speaker 1: television maybe, But in your skin, melanocytes produce the pigments

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Speaker 1: that help give your skin its tone. Whatever color your

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Speaker 1: skin is, it contains an average of one thousand, two

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Speaker 1: hundred melanocytes per square millimeter. Your genes and various factors

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Speaker 1: in your environment tell your melanocytes how much melanin to

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Speaker 1: produce and what types. One of those environmental factors is

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Speaker 1: ultra violet radiation, probably from sunlight or maybe from black

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Speaker 1: lights at raves, and cellular biology is really complicated. To

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Speaker 1: paraphrase in Ego Montoya, I'm just going to sum up.

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Speaker 1: When certain types of ultra violet photons pass into your skin,

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Speaker 1: as specifically into your keratinocytes there and smack into molecules

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Speaker 1: of your DNA, those photons cause minor damage that sets

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Speaker 1: off a chain reaction. The end result, your melanocytes go

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Speaker 1: into overdrive producing melanin particles. Your melanocytes carefully pack those

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Speaker 1: melanine particles into special organelles called melanosomes, sort of like

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Speaker 1: little intercellular shipping boxes. These melanin packages moved to the

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Speaker 1: very edges of the melano site and neighboring carrotino sites

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Speaker 1: bite the melanosomes right out of the cell and absorb them.

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Speaker 1: It doesn't hurt the melano syte. It just sounds creepy

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Speaker 1: because it is okay, so you catch some sun. If

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Speaker 1: your melanocytes and therefore your melanin packed melanosomes, are spread

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Speaker 1: evenly around among your carrotino sites, you tan. But if

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Speaker 1: your melanosytes are clustered together, you freckle. Either way, the

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Speaker 1: melanin particles absorb incoming u V radiation and transform it

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Speaker 1: into infrared radiation, which is just low level heat. Thus,

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Speaker 1: your delicate squidge insides and your cells DNA are protected

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Speaker 1: from further UV damage. Without frequent sun exposure, tans and

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Speaker 1: freckles fade over to time because your caroteno sites don't

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Speaker 1: last forever. As new skin cells grow and mature, your

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Speaker 1: old caroteno sites are eventually pushed to the very surface

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Speaker 1: of your skin, where they become dehydrated and die. And

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Speaker 1: that's right. The cells on the surface of our skin,

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Speaker 1: the ones that we can see and touch, are actually dead.

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Speaker 1: But it's for a good cause. During the process of

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Speaker 1: drying out and dyeing, your caroteno sites become the strong,

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Speaker 1: durable layer that makes our skin so effective at keeping

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Speaker 1: blood in and germs out. And when your caroteno sites

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Speaker 1: move on to that big skin layer on the surface,

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Speaker 1: they bring any melanin that they've collected along with them.

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Speaker 1: And when those cells slough off through normal wear and tear,

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Speaker 1: the melanin goes to and your skin returns to its

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Speaker 1: usual pigment, which in my case is translucent like a

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Speaker 1: deep sea shrimp. Today's episode was written by me and

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Speaker 1: produced by Tyler Klang. Check out our online store at

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Speaker 1: and lots of other sunny topics, visit our home planet,

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Speaker 1: how stuff Works dot com.