WEBVTT - How Does Skin Tan and Burn? 0:00:01.840 --> 0:00:07.520 Welcome to Brainstuff, a production of iHeartRadio. Hey brain Stuff, 0:00:07.560 --> 0:00:12.560 Lauren vogelbaumb here. The warm sun can feel so good 0:00:12.560 --> 0:00:15.000 on your skin, and getting a bit of color from 0:00:15.040 --> 0:00:18.040 it can be beautiful. But we all know it's important 0:00:18.040 --> 0:00:20.600 to protect ourselves from the damage that the sun can do. 0:00:21.680 --> 0:00:24.520 Our planet does a fairly good job of protecting us. 0:00:25.000 --> 0:00:28.080 You might remember from our Sunburns in Space episode that 0:00:28.240 --> 0:00:31.920 Earth's ozone layer absorbs nearly all of the damaging ultraviolet 0:00:32.000 --> 0:00:36.240 light that the sun puts off. Sunscreen, sunglasses, and appropriate 0:00:36.280 --> 0:00:38.960 clothing can help us defend against the UV light that 0:00:39.040 --> 0:00:42.960 does get through. But today let's talk about our first 0:00:43.120 --> 0:00:47.559 line of defense, our skin. Skin is one of the 0:00:47.560 --> 0:00:51.000 most amazing organs of the human body. It's weird to 0:00:51.000 --> 0:00:52.800 think of it as an organ because we tend to 0:00:52.800 --> 0:00:57.480 think of organs as these sort of boxy things. Your heart, liver, kidneys, 0:00:57.760 --> 0:01:02.400 those are obviously organs. But an organ, by definition, is 0:01:02.440 --> 0:01:05.680 a structure made up of cells and tissues that performs 0:01:05.880 --> 0:01:09.600 or helps perform some function in our body, which definitely 0:01:09.640 --> 0:01:14.480 applies to skin. Skin is made up of very specific 0:01:14.560 --> 0:01:17.839 cells and tissues, and their collective purpose is to act 0:01:17.880 --> 0:01:22.160 as the boundary between you and the world. Most of 0:01:22.160 --> 0:01:25.120 our organs don't directly interface with the world around us, 0:01:25.160 --> 0:01:27.679 but the skin does, which is why it's loaded with 0:01:27.760 --> 0:01:30.959 sensors and has a very tough layered design so that 0:01:31.000 --> 0:01:36.240 it can handle things like abrasion and sunlight. Our skin 0:01:36.319 --> 0:01:39.040 is made up of three main layers, the epidermis on 0:01:39.080 --> 0:01:42.080 the outside, the dermis in the middle, and the hypodermis 0:01:42.080 --> 0:01:45.600 on the inside. The epidermis is the barrier. The dermis 0:01:45.600 --> 0:01:49.360 contains all of the equipment, things like nerve endings, sweat glands, 0:01:49.400 --> 0:01:54.160 hair follicles, and so on, and the hypodermis provides structural support, 0:01:54.680 --> 0:01:58.800 also called the subcutaneous layer. The hypodermis contains fat to 0:01:59.040 --> 0:02:02.440 insulate and protect are underlying muscles and organs, plus blood 0:02:02.520 --> 0:02:07.200 vessels to supply the equipment in the dermis. But today 0:02:07.400 --> 0:02:11.359 let's focus in on the epidermis. The epidermis itself has 0:02:11.400 --> 0:02:14.240 two main layers, the inner of which is living and 0:02:14.280 --> 0:02:17.639 the outer of which is dead. The dead skin cells 0:02:17.639 --> 0:02:20.080 of the outer layer are what we see and touch, 0:02:20.400 --> 0:02:24.280 and it's called the stratium corneum. The cells in this 0:02:24.360 --> 0:02:27.880 layer are filled with a protein called keratin. Keratin is 0:02:27.880 --> 0:02:32.840 interesting because it's tough. Horns, hair, hoofs, fingernails, and feathers 0:02:33.080 --> 0:02:36.440 all gain their strength from keratin. Yes, the same stuff 0:02:36.440 --> 0:02:39.440 that your fingernails are made of actually forms your visible skin, 0:02:39.919 --> 0:02:43.680 but in a much thinner and more flexible layer. That 0:02:43.760 --> 0:02:47.120 is what makes your skin so tough. In parts of 0:02:47.120 --> 0:02:48.920 the body that get a lot of wear, like the 0:02:48.960 --> 0:02:51.160 palms of the hands and soles of the feet, the 0:02:51.200 --> 0:02:55.600 stratium cornium is thicker to handle the abrasion. The cells 0:02:55.600 --> 0:02:58.720 of this layer are constantly flaking off and being replaced 0:02:58.720 --> 0:03:03.400 by newer, dead skins being pushed outward. Those cells are 0:03:03.440 --> 0:03:06.160 created in the living inner layer of the epidermis, which 0:03:06.200 --> 0:03:09.639 is called the malpigean layer. It sidles up to the dermis, 0:03:09.639 --> 0:03:12.680 which feeds and supports it, and this is where the 0:03:12.720 --> 0:03:17.040 sun affects our skin When we ten. The innermost part 0:03:17.040 --> 0:03:19.880 of the malpagean layer, called the basal layer, is where 0:03:19.919 --> 0:03:23.079 we produce those new tough outer skin cells, and also 0:03:23.280 --> 0:03:27.959 where we produce melanin. Melanins are a group of pigments 0:03:27.960 --> 0:03:30.800 found in several places in our bodies, but most relevant 0:03:30.800 --> 0:03:34.960 today in our eyes, skin, and hair. The two main 0:03:35.040 --> 0:03:37.920 types of melanin found there are eumelanin, which can be 0:03:38.000 --> 0:03:40.960 brown to black in color, and fiamelanin, which can be 0:03:41.040 --> 0:03:46.320 yellow to red. They're produced by cells called melanocytes, and 0:03:46.400 --> 0:03:49.400 no matter what color your skin is, it contains about 0:03:49.400 --> 0:03:53.320 one thy two hundred melanocytes per square millimeter, which is 0:03:53.480 --> 0:03:56.480 four hundreds of an inch, which is really small, which 0:03:56.520 --> 0:03:59.760 means that we have a lot of melanocytes. Our skin 0:03:59.800 --> 0:04:02.640 color is determined by how much and what types of 0:04:02.680 --> 0:04:08.760 melanin those cells produce. So okay, when your skin tans 0:04:08.920 --> 0:04:12.320 or deepens in color, what's happening is that your melanocytes 0:04:12.360 --> 0:04:15.800 are producing eumelanin pigment in reaction to the ultraviolet light. 0:04:16.120 --> 0:04:19.800 In sunlight, ev light can damage our cells, and our 0:04:19.839 --> 0:04:24.719 bodies evolved the ability to mitigate that with eumelanin. Eumelanin 0:04:24.839 --> 0:04:28.760 absorbs ultraviolet light and thus protects our cells from damage. 0:04:29.120 --> 0:04:32.720 So our bodies developed this technique that when we're exposed 0:04:32.760 --> 0:04:37.520 to UV light that stimulates the production of melanin. A 0:04:37.560 --> 0:04:40.680 melanin production takes a fair amount of time. That's why 0:04:40.720 --> 0:04:42.920 most people can't get a ten in a single day. 0:04:43.760 --> 0:04:46.160 First you have to expose yourself to UV light for 0:04:46.200 --> 0:04:49.480 a short period of time to activate the melanocytes. They 0:04:49.520 --> 0:04:52.440 produce melanin over the course of a few hours, and 0:04:52.560 --> 0:04:55.760 by repeating this process over five to seven days, pigment 0:04:55.760 --> 0:04:57.880 builds up in your cells to a level that's more 0:04:57.880 --> 0:05:03.760 protective than your baseline. Of course, people's baseline of melanin 0:05:03.839 --> 0:05:07.560 can vary wildly. People with darker skin are lucky to 0:05:07.600 --> 0:05:11.320 have elevated protection from UV radiation all the time. That 0:05:11.400 --> 0:05:15.200 doesn't mean you shouldn't wear sun protection though. Also your 0:05:15.279 --> 0:05:19.000 balance of types of melanin matters. Again. Eumelanin is what 0:05:19.080 --> 0:05:22.960 creates a tan, so people whose skin produces more feomelanin 0:05:23.080 --> 0:05:26.800 and less eumelanin, like many light skinned redheads, don't tan 0:05:26.960 --> 0:05:31.080 very well. This is caused by variations in a particular gene, 0:05:31.160 --> 0:05:34.600 the MC one R gene, to be specific. This gene 0:05:34.640 --> 0:05:38.840 also controls whether you freckle. Freckles are spots of hyperpigmentation 0:05:39.080 --> 0:05:42.839 where for some reason, your skin clusters production of eumelanin 0:05:42.960 --> 0:05:46.400 instead of spreading it out. People with albinism have no 0:05:46.520 --> 0:05:49.760 melanin in their skin, hair, or eyes. The chemical pathway 0:05:49.800 --> 0:05:53.560 that produces melanin can't proceed because an enzyme called tyrosinase 0:05:53.680 --> 0:05:56.960 is missing. But no matter what your skin color or 0:05:57.000 --> 0:06:00.400 whether it deepens with sun exposure, getting too much sun 0:06:00.520 --> 0:06:04.360 can cause damage to your skin. In the short term, 0:06:04.440 --> 0:06:07.080 too much sun can cause a sunburn, leaving your skin 0:06:07.160 --> 0:06:11.760 red and painfully tender, and sometimes even blistered. When you 0:06:11.800 --> 0:06:14.719 get a sunburn, what you're really getting is cellular damage 0:06:14.760 --> 0:06:18.400 from ultraviolet light. The body responds to the damage with 0:06:18.480 --> 0:06:21.320 increased blood flow to the capillary bed of the dermis 0:06:21.320 --> 0:06:24.400 in order to bring in cells to repair that damage. 0:06:24.800 --> 0:06:27.560 The extra blood in the capillaries is what causes redness. 0:06:27.960 --> 0:06:30.360 That's why if you press on sunburned skin, that will 0:06:30.360 --> 0:06:33.720 turn white and then return to red as the capillaries refill. 0:06:35.160 --> 0:06:38.280 In the long term, uv light can break down elastin 0:06:38.360 --> 0:06:41.720 fibers in your skin, which help give skin its bouncy structure. 0:06:42.560 --> 0:06:45.000 The cells throughout your skin's layers can be damaged too, 0:06:45.360 --> 0:06:49.000 of forcing them to repair themselves over time. This stress 0:06:49.000 --> 0:06:52.119 can affect the cell's DNA, which makes them less able 0:06:52.160 --> 0:06:55.440 to produce new cells and function properly. All of this 0:06:55.560 --> 0:06:59.080 can cause visible signs of aging, like wrinkles in sunspots, 0:06:59.480 --> 0:07:03.279 but more importantly can cause pancers like melanoma or basal 0:07:03.320 --> 0:07:06.280 cell carcinoma, but which start with damage in the melanocytes 0:07:06.320 --> 0:07:10.720 and those basal layer cells, respectively. All of this is 0:07:10.760 --> 0:07:13.360 why it's really good to wear protection when you're going 0:07:13.400 --> 0:07:16.480 to be outside during daylight hours, especially if it's sunny. 0:07:16.600 --> 0:07:21.080 But even if it's cloudy, BEUV light is still there. Hats, sunglasses, 0:07:21.120 --> 0:07:23.720 and long sleeves and pants or skirts can all help 0:07:23.720 --> 0:07:25.960 block it. But let's talk about the layer you put 0:07:25.960 --> 0:07:31.119 on first. Sunscreen sunscreens are designed to either physically block 0:07:31.320 --> 0:07:34.640 or chemically absorb UV light before it can reach your skin. 0:07:35.640 --> 0:07:39.160 Creams that go on white are usually physical blockers. That 0:07:39.200 --> 0:07:41.840 white tint is from fine particles of minerals like a 0:07:41.880 --> 0:07:46.400 titanium dioxide or zinc oxide, that reflect UV light. They 0:07:46.440 --> 0:07:48.440 can look a little chalky on your skin, but they 0:07:48.520 --> 0:07:53.320 usually don't cause any irritation. Chemical sunscreens absorb UV light 0:07:53.560 --> 0:07:56.559 and in doing so, emit a very low level of heat. 0:07:57.080 --> 0:07:59.640 Usually it's too low to notice, but these sunscreens are 0:07:59.680 --> 0:08:03.520 more lightly to cause irritation or an allergic reaction. Some 0:08:03.560 --> 0:08:08.119 formulas contain both physical and chemical elements. Look for broad 0:08:08.160 --> 0:08:11.480 spectrum sunscreens that means that they block a wider range 0:08:11.480 --> 0:08:15.000 of types of ultraviolet light, and look for waterproof or 0:08:15.160 --> 0:08:20.800 sport formulas. Find one that's SPF thirty or higher. SPF 0:08:20.840 --> 0:08:24.280 stands for sun protection factor, and the number refers to 0:08:24.320 --> 0:08:28.880 how much UV light the product blocks SPF ten, For example, 0:08:29.040 --> 0:08:31.720 let's one tenth of UV light through or ten percent 0:08:32.080 --> 0:08:35.120 SPF thirty only, let's one thirtieth of UV light through 0:08:35.280 --> 0:08:38.960 or three percent. After that, you get diminishing returns because 0:08:39.000 --> 0:08:42.080 of how fractions work. It can be worth it, though, 0:08:42.120 --> 0:08:45.920 if your skin is light and you don't tan in 0:08:45.960 --> 0:08:49.280 any case, you want to apply sunscreen generously about half 0:08:49.320 --> 0:08:51.720 an hour before you'll be outside to give it time 0:08:51.760 --> 0:08:55.280 to settle into your skin. Reap every couple hours or 0:08:55.280 --> 0:08:57.160 more often if you think that you might have swam 0:08:57.280 --> 0:09:02.840 or sweat or toweled your initial application off. Interestingly, in 0:09:02.920 --> 0:09:06.360 people who do tan, the stimulation of melanin production can 0:09:06.400 --> 0:09:10.080 happen when UV light hits your skin or your eyes. 0:09:11.200 --> 0:09:13.880 Melanocytes are prompted to produce more melanin when they receive 0:09:13.920 --> 0:09:18.960 a hormone called appropriately melanocyte stimulating hormone. This hormone can 0:09:19.000 --> 0:09:21.600 be produced locally by skin cells that are exposed to 0:09:21.679 --> 0:09:25.040 UV light, but it's also produced by the pituitary gland, 0:09:25.200 --> 0:09:28.960 where many of our hormones are produced. The pituitary gland 0:09:29.040 --> 0:09:31.440 is tied into the optic nerve, which means that it 0:09:31.480 --> 0:09:35.160 responds to light that comes in through your eyes. So 0:09:35.480 --> 0:09:38.520 when you wear sunglasses in bright sunlight and block some 0:09:38.559 --> 0:09:41.239 of that UV light from hitting your eyes, your petuitary 0:09:41.280 --> 0:09:45.040 gland produces less of the melanocyte stimulating hormone and you 0:09:45.080 --> 0:09:49.000 won't tan as much, which is why a sun blocking 0:09:49.080 --> 0:09:53.320 system of eye protection, appropriate clothing and sunscreen is the 0:09:53.360 --> 0:10:01.160 best way to prevent sun damage. Today's episode is based 0:10:01.200 --> 0:10:04.280 on the article how Sunburns and suntan's work on HowStuffWorks 0:10:04.280 --> 0:10:07.240 dot Com, written by Marshall Brain Brain Stuff is production 0:10:07.320 --> 0:10:09.760 by Heart Radio in partnership with HowStuffWorks dot Com and 0:10:09.880 --> 0:10:13.120 is produced by Tyler Klang. For more podcasts my heart Radio, 0:10:13.320 --> 0:10:16.319 visit the iHeartRadio app, Apple Podcasts, or wherever you listen 0:10:16.360 --> 0:10:17.360 to your favorite shows.