Now that we are getting into the thick of summertime activities, sunburn is something to consider. If you go out on a sunny day and stay in the sun too long, you will get a sunburn. How is it that light can cause the skin to burn? 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?

Your skin is one of the most amazing organs in your body. In fact, it is the largest organ you have. The skin of a typical adult weighs about 8 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 to handle things like abrasion and sunlight.

The easiest way to get a sunburn is to stay inside for a month or two and then spend a day outside on a sunny 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 UV light penetrates into living skin cells, and it starts damaging and killing those cells.

When your skin is sunburned, your body needs to repair the damage. The repair process starts when damaged cells release chemicals that notify the body 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 ways to avoid sunburn. You can stay inside, cover all your skin with clothing or use sunscreen. Sunscreen contains chemicals that absorb UV light, preventing it from getting to the living cells in your skin.

Darker skin, either natural or suntanned, does offer some protection from the sun. The outer layer of skin, called the stratum cornea, contains the dead skin cells that cover your body. Below the stratum cornea is the granular layer, which generates the dead cells. Below that is the basal layer where tanning happens. The basal layer contains special cells called melanocytes. When a melanocyte detects UV light, it creates a brown pigment called melanin. Melanin, like sunscreen, absorbs UV light and protects your skin from damage.

Contact Marshall Brain at marshall.brain@howstuffworks.com.