Welcome to brain stuff from how stuff works. Hey, brain stuff, Lauren Volga bomb here when the weather is nice, I've been made to understand that some people enjoy spending time outdoors where they're exposed to, among other things, sunlight. Stuff in sunlight can make stuff in your skin produce more pigment, which shows up as freckles or a tan. But how why? Scientifically speaking, the skin freckling tan both happen in your epidermis, which is the tough, resilient frosting on our body's cake.
Under normal circumstances, it protects and helps hold in our precious, squishy insides. Your epidermis contains a few kinds of cells, but the ones were primarily concerned with here are the carrotino sites and the melano sites. Carrotino sites make up most of your epidermis. There are skin cells that are maturing and getting pushed upward towards your skin surface by new cell growth. Melano sites are specialized cells that create pigmented proteins called melanin. And by the way, they're not
only found in our skin. Melanocytes are also at work in your eyes and hair, giving them their color, and in your heart inner ear and brain doing. No one is really sure what conspiring to make you enjoy reality television maybe, But in your skin, melanocytes produce the pigments that help give your skin its tone. Whatever color your skin is, it contains an average of one thousand, two
hundred melanocytes per square millimeter. Your genes and various factors in your environment tell your melanocytes how much melanin to produce and what types. One of those environmental factors is ultra violet radiation, probably from sunlight or maybe from black lights at raves, and cellular biology is really complicated. To paraphrase in Ego Montoya, I'm just going to sum up.
When certain types of ultra violet photons pass into your skin, as specifically into your keratinocytes there and smack into molecules of your DNA, those photons cause minor damage that sets off a chain reaction. The end result, your melanocytes go into overdrive producing melanin particles. Your melanocytes carefully pack those melanine particles into special organelles called melanosomes, sort of like
little intercellular shipping boxes. These melanin packages moved to the very edges of the melano site and neighboring carrotino sites bite the melanosomes right out of the cell and absorb them. It doesn't hurt the melano syte. It just sounds creepy because it is okay, so you catch some sun. If your melanocytes and therefore your melanin packed melanosomes, are spread evenly around among your carrotino sites, you tan. But if
your melanosytes are clustered together, you freckle. Either way, the melanin particles absorb incoming u V radiation and transform it into infrared radiation, which is just low level heat. Thus, your delicate squidge insides and your cells DNA are protected from further UV damage. Without frequent sun exposure, tans and freckles fade over to time because your caroteno sites don't last forever. As new skin cells grow and mature, your old caroteno sites are eventually pushed to the very surface
of your skin, where they become dehydrated and die. And that's right. The cells on the surface of our skin, the ones that we can see and touch, are actually dead. But it's for a good cause. During the process of drying out and dyeing, your caroteno sites become the strong, durable layer that makes our skin so effective at keeping blood in and germs out. And when your caroteno sites move on to that big skin layer on the surface, they bring any melanin that they've collected along with them.
And when those cells slough off through normal wear and tear, the melanin goes to and your skin returns to its usual pigment, which in my case is translucent like a deep sea shrimp. Today's episode was written by me and produced by Tyler Klang. Check out our online store at t public dot com slash brain stuff to find brainy designs printed on every type of shirt imaginable, and every
purchase supports us directly. Of course. For more on this and lots of other sunny topics, visit our home planet, how stuff Works dot com.