You may not really think of the Skin as an organ, like the heart and lungs. To many people, skin seems more like a simple cover to prevent their insides from falling out. An organ is a somewhat independent part of the human body that performs a specific function.
Once you know that, you can see that the skin is an organ, because it performs the following specific functions (in addition to others):
1. Protects your body from infection
2. Serves as a waterproof barrier between you and the outside world
3. Shields you from the sun’s harmful rays
4. Provides cushioning like a shock absorber that defends you from injury
5. Insulates your body and keeps your temperature right around a cozy 98.6 degrees Fahrenheit (37 degrees Celsius)
6. Acts as an energy reserve
7. Alerts you to potential harm through your sensations of touch and pain
8. Repairs itself (that’s why cuts heal)
9. Produces vitamin D
Because your skin has so many functions, you may not be surprised to discover that it also has a rather complicated structure with many working parts. It contains hairs that have their own oil glands and tiny muscles — I’ll bet that you didn’t know that hairs have muscles! Your skin has sensory nerves — hot, cold, touch, and pressure receptors. It also is home to blood vessels, lymph vessels, and sweat glands. Plus, your skin has microscopic pigmentproducing cells, cells that work on your immunity, as well as cells that protect and replace themselves. With all that going on, you
may be surprised that your skin doesn’t have its own zip code.

Human skin is made up of three layers. First come the top two layers — the epidermis (the outside layer of skin that you can touch and see) and the dermis (which is located directly beneath the epidermis). Then comes the third, bottom fatty layer that the epidermis and dermis rest upon, which is called the subcutaneous layer.
The prefix epi means “upon” and derm means “skin,” so, together, they form epidermis (upon the skin). And obviously, dermis means “skin.” The prefix sub means “under” and cutaneous is another reference to “skin,” so the word subcutaneous means “under the skin.” (I guess they should have named it the “subdermis” if they wanted
to be totally consistent.)