Why is it that when you go out on a bright summer day and spend an hour or so in the sun, you most likely get a sunburn? That is, unless you've taken the time before that to get a nice gradual tan. If you have a tan, you can go out in the sun and not get burned. Of course, none of this applies if you have "fair skin." The fair-skinned among us never get a tan, so they always get burned. If you take the time to look at skin and sunlight in some detail, all of this begins to make sense, and you can learn a lot about your body in the process.
Skin is one of the most amazing organs in the human body. It is hard for us to think about it as an organ, however. We tend to think of organs as boxy things. Your heart, liver, kidneys - those are obviously organs. But skin is an organ too. @Merriam-Webster Collegiate Dictionary defines an organ as a) a differentiated structure (as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism; or b) bodily parts performing a function or cooperating in an activity."
