How Does Skin Tan and Burn?

light that the sun puts off. Sunscreen, sunglasses, and appropriate clothing can help us defend against the UV light that does get through. But today let's talk about our first line of defense, our skin. Skin is one of the most amazing organs of the human body. It's weird to think of it as an organ because we tend to think of organs as these sort of boxy things. Your heart, liver, kidneys,

those are obviously organs. But an organ, by definition, is a structure made up of cells and tissues that performs or helps perform some function in our body, which definitely applies to skin. Skin is made up of very specific cells and tissues, and their collective purpose is to act as the boundary between you and the world. Most of our organs don't directly interface with the world around us, but the skin does, which is why it's loaded with sensors and has a very tough layered design so that

it can handle things like abrasion and sunlight. Our skin is made up of three main layers, the epidermis on the outside, the dermis in the middle, and the hypodermis on the inside. The epidermis is the barrier. The dermis contains all of the equipment, things like nerve endings, sweat glands, hair follicles, and so on, and the hypodermis provides structural support,

also called the subcutaneous layer. The hypodermis contains fat to insulate and protect are underlying muscles and organs, plus blood vessels to supply the equipment in the dermis. But today let's focus in on the epidermis. The epidermis itself has two main layers, the inner of which is living and the outer of which is dead. The dead skin cells of the outer layer are what we see and touch, and it's called the stratium corneum. The cells in this

layer are filled with a protein called keratin. Keratin is interesting because it's tough. Horns, hair, hoofs, fingernails, and feathers all gain their strength from keratin. Yes, the same stuff that your fingernails are made of actually forms your visible skin, but in a much thinner and more flexible layer. That is what makes your skin so tough. In parts of the body that get a lot of wear, like the palms of the hands and soles of the feet, the

stratium cornium is thicker to handle the abrasion. The cells of this layer are constantly flaking off and being replaced by newer, dead skins being pushed outward. Those cells are created in the living inner layer of the epidermis, which is called the malpigean layer. It sidles up to the dermis, which feeds and supports it, and this is where the

sun affects our skin When we ten. The innermost part of the malpagean layer, called the basal layer, is where we produce those new tough outer skin cells, and also where we produce melanin. Melanins are a group of pigments found in several places in our bodies, but most relevant today in our eyes, skin, and hair. The two main types of melanin found there are eumelanin, which can be brown to black in color, and fiamelanin, which can be

yellow to red. They're produced by cells called melanocytes, and no matter what color your skin is, it contains about one thy two hundred melanocytes per square millimeter, which is four hundreds of an inch, which is really small, which means that we have a lot of melanocytes. Our skin color is determined by how much and what types of

melanin those cells produce. So okay, when your skin tans or deepens in color, what's happening is that your melanocytes are producing eumelanin pigment in reaction to the ultraviolet light. In sunlight, ev light can damage our cells, and our bodies evolved the ability to mitigate that with eumelanin. Eumelanin absorbs ultraviolet light and thus protects our cells from damage. So our bodies developed this technique that when we're exposed to UV light that stimulates the production of melanin. A

melanin production takes a fair amount of time. That's why most people can't get a ten in a single day. First you have to expose yourself to UV light for a short period of time to activate the melanocytes. They produce melanin over the course of a few hours, and by repeating this process over five to seven days, pigment builds up in your cells to a level that's more protective than your baseline. Of course, people's baseline of melanin can vary wildly. People with darker skin are lucky to

have elevated protection from UV radiation all the time. That doesn't mean you shouldn't wear sun protection though. Also your balance of types of melanin matters. Again. Eumelanin is what creates a tan, so people whose skin produces more feomelanin and less eumelanin, like many light skinned redheads, don't tan very well. This is caused by variations in a particular gene, the MC one R gene, to be specific. This gene

also controls whether you freckle. Freckles are spots of hyperpigmentation where for some reason, your skin clusters production of eumelanin instead of spreading it out. People with albinism have no melanin in their skin, hair, or eyes. The chemical pathway that produces melanin can't proceed because an enzyme called tyrosinase is missing. But no matter what your skin color or whether it deepens with sun exposure, getting too much sun

can cause damage to your skin. In the short term, too much sun can cause a sunburn, leaving your skin red and painfully tender, and sometimes even blistered. When you get a sunburn, what you're really getting is cellular damage from ultraviolet light. The body responds to the damage with increased blood flow to the capillary bed of the dermis in order to bring in cells to repair that damage. The extra blood in the capillaries is what causes redness.

That's why if you press on sunburned skin, that will turn white and then return to red as the capillaries refill. In the long term, uv light can break down elastin fibers in your skin, which help give skin its bouncy structure. The cells throughout your skin's layers can be damaged too, of forcing them to repair themselves over time. This stress can affect the cell's DNA, which makes them less able

to produce new cells and function properly. All of this can cause visible signs of aging, like wrinkles in sunspots, but more importantly can cause pancers like melanoma or basal cell carcinoma, but which start with damage in the melanocytes and those basal layer cells, respectively. All of this is why it's really good to wear protection when you're going to be outside during daylight hours, especially if it's sunny.

But even if it's cloudy, BEUV light is still there. Hats, sunglasses, and long sleeves and pants or skirts can all help block it. But let's talk about the layer you put on first. Sunscreen sunscreens are designed to either physically block or chemically absorb UV light before it can reach your skin. Creams that go on white are usually physical blockers. That white tint is from fine particles of minerals like a

titanium dioxide or zinc oxide, that reflect UV light. They can look a little chalky on your skin, but they usually don't cause any irritation. Chemical sunscreens absorb UV light and in doing so, emit a very low level of heat. Usually it's too low to notice, but these sunscreens are more lightly to cause irritation or an allergic reaction. Some

formulas contain both physical and chemical elements. Look for broad spectrum sunscreens that means that they block a wider range of types of ultraviolet light, and look for waterproof or sport formulas. Find one that's SPF thirty or higher. SPF stands for sun protection factor, and the number refers to how much UV light the product blocks SPF ten, For example, let's one tenth of UV light through or ten percent SPF thirty only, let's one thirtieth of UV light through

or three percent. After that, you get diminishing returns because of how fractions work. It can be worth it, though, if your skin is light and you don't tan in any case, you want to apply sunscreen generously about half an hour before you'll be outside to give it time to settle into your skin. Reap every couple hours or more often if you think that you might have swam

or sweat or toweled your initial application off. Interestingly, in people who do tan, the stimulation of melanin production can happen when UV light hits your skin or your eyes. Melanocytes are prompted to produce more melanin when they receive a hormone called appropriately melanocyte stimulating hormone. This hormone can be produced locally by skin cells that are exposed to UV light, but it's also produced by the pituitary gland,

where many of our hormones are produced. The pituitary gland is tied into the optic nerve, which means that it responds to light that comes in through your eyes. So when you wear sunglasses in bright sunlight and block some of that UV light from hitting your eyes, your petuitary gland produces less of the melanocyte stimulating hormone and you won't tan as much, which is why a sun blocking system of eye protection, appropriate clothing and sunscreen is the

best way to prevent sun damage. Today's episode is based on the article how Sunburns and suntan's work on HowStuffWorks dot Com, written by Marshall Brain Brain Stuff is production by Heart Radio in partnership with HowStuffWorks dot Com and is produced by Tyler Klang. For more podcasts my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.