The next time you use the expression “I know it like the back of my hand,” consider this. One square inch of your skin is home to:

• 65 hairs

• 100 sebaceous glands

• 78 yards of nerves

• 650 sweat glands

• 19 yards of blood vessels

• 9,500,000 cells

• 1,300 nerve endings

• 20,000 sensory cells

just to name… um… a few. Our body’s largest organ makes up about 15% of our total weight and covers 20 square feet. Paper-thin and incredibly complex, your skin protects you from the perils of your environment and allows you to feel pain and pleasure. It’s working to renew itself every second of every day. So how well do you really know the back of your hand — or for that matter, any square inch of your skin?


Introducing the epidermis. No matter how modest you are, your epidermis is always showing. It’s the top layer of your skin, the one you show to the world — and like your other organs, it has to work constantly to keep you alive. The very top layer is actually made up of dead cells, or corneocytes. This outer layer acts as your body’s natural suit of armor, protecting you from the sun, wind and rain. As your skin renews itself, the dead cells gradually slough off to make room for new ones, which are forming at the base of the epidermis. Once the new cells are ready, they begin to travel up through the epidermal layer, where they gradually replace the dead cells. If you followed the progress of one cell, the whole process would take about a month. But it’s happening constantly — in fact, in the time it took you to read this, you’ve probably lost about 40,000 cells. Luckily, 95% of your epidermis is working to create new cells. The other 5% are composed of melanocytes, which produce melanin, the substance that gives your skin its color; and Langerhan cells, which work with the immune system to help you fight off disease.

The delicate dermis. Below the epidermis is the dermis, which serves as a foundation for the epidermis and makes up the principal mass of the skin. This layer produces collagen, elastin and reticulin, the substances that lend structure and support to your largest organ. The dermis also houses nerve endings, blood vessels, oil glands and sweat glands — the various engine parts that keep the skin in working order. Nerve endings allow you to feel the sun on your face and the sand between your toes; they also tell you when to put on more sunscreen or get out of the water because it’s too cold. Sweat glands help keep your skin cool; oil glands produce sebum, which keeps your skin soft, pliable and waterproof. And all the while, blood vessels are working to supply the skin with the nutrients it needs to keep replenishing itself, and carry waste products to the lungs for oxygenation and renewal.

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