Now that we are getting into the thick of summertime activities, sunburn is something that you have to think about. If you go out on a bright sunny day and stay in the sun too long, you will get sunburn. But have you ever wondered what is actually happening? How is it that light can cause such intense pain? And why is it that if you take the time to get a gradual tan, you can stay out in the sun all day without getting burned at all? It is time to find out how sunburn works.
Your skin is one of the most amazing organs in your body. We tend to think of organs as boxy things - your heart, liver, kidneys - those are obviously organs. But skin is an organ too. In fact, it is the largest organ you have. The skin of a typical adult weighs about eight pounds and covers about 20 square feet. Skin is loaded with sensors, blood vessels, sweat glands, hair follicles and muscles (one tiny muscle for each hair) and it has a very tough layered design so that it can handle things like abrasion and sunlight.
If skin is so great, the why do people get sunburn? It has to do with a quirk in the design of the skin, plus the fact that nature never intended for human beings to stay inside all day.
The easiest way to get sunburn is to stay inside for a month or two and then spend a day outside on a sunny summer day. If you are a Caucasian, your skin will have no protection from the ultraviolet light in sunlight. When you go out in the sun, the ultraviolet light penetrates into living skin cells, and it starts damaging and killing those cells.
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Whether you hit your finger with a hammer, cut yourself or get a sunburn, your body needs to repair the damage. The repair process starts when damaged cells release chemicals. These chemicals notify your body and tell it that damage has taken place. The first thing the chemicals do is set off pain signals in your skin's pain sensors. Those same chemicals also tell your body to send in lots of white blood cells to eat all the damaged and dead cells. The white blood cells arrive in the blood stream, so your body dilates all the capillaries in the damaged area to increase blood flow. So your sunburned skin turns red and hot because of all of those dilated capillaries bringing in the white blood cells. And your skin stings because every pain sensor is your sunburned skin is sounding the, "Hey, there is damage here!" alarm.
There are three ways you can avoid sunburn. One is to stay inside or cover all your skin with clothing. No sun means no sunburn. The second way is to use a sunscreen. Sunscreen contains chemicals that absorb ultraviolet light. All the UV light gets absorbed by the sunscreen chemicals and never makes it to the living cells in your skin. The third way is to go out in the sun a little bit each day and get a tan. The tan will protect your skin from sunburn.
Here's how a tan works. If you look at a cross section of your skin, you have the outer layer called the stratum cornea. This layer contains the dead skin cells that you actually see covering your body. These dead cells are loaded with keratin - the same protein that makes fingernails so tough - so your skin is surprisingly strong. Below the stratum cornea is the granular layer (the layer that generates the dead cells), and below that is the basal layer. Tanning happens in the basal layer because the basal layer contains special cells called melanocytes. When a melanocyte detects ultraviolet light, it creates a brown pigment called melanin. Melanin, like sunscreen, absorbs ultraviolet light and protects your skin from damage.
So, why doesn't your skin produce melanin all the time to provide constant protection from sunburn? In many people it does. But in Caucasians, who historically lived in much colder regions that have a lot less sunlight than equatorial regions, there is a problem. Your skin actually uses ultraviolet light to synthesize vitamin D. When there is less sunlight in winter, the skin of Caucasians eliminates the melanin to make sure there is enough vitamin D.
In other words, if people spent all their time outdoors, the skin of Caucasians would naturally tan and untan with the seasons and you would never get a sunburn.