The Skinny on Skin

The skin is your body's largest organ. It protects you against bacteria, viruses, dirt, wind, heat and cold. And it serves as a window to the body, alerting doctors when something is wrong.

Your skin needs a steady supply of new cells to protect the organs against infection, the elements and other invaders. New skin cells, manufactured in the epidermis, migrate to the outer layer of skin. One square inch of skin contains millions of cells, blood vessels, nerve endings and sweat glands.

Your skin also regulates heat. Blood vessels in the skin widen when it's hot, evaporating perspiration and cooling the body. They narrow when your body is cold, reducing the amount of heat you lose through your body's largest organ.

Your skin is really made up of three distinct layers: the epidermis, the dermis and subcutaneous tissue.

Epidermis

Highly specialized cells here produce substances called keratin and melanin. Keratin covers the skin with a paper-thin layer that's the body's first defense against invaders. Melanin gives skin its pigment, or color, to help protect us against the sun's ultraviolet (UV) rays.

Dermis

This second layer is elastic and fibrous, holding a network of blood vessels that feed and support other layers of skin, hair, nails, sweat glands and nerves.

Subcutaneous tissue

This deepest level is composed primarily of fat that the body uses as a cushion. A network of blood vessels and nerves runs through this layer below the epidermis and dermis.

Protecting your skin

The best way to keep your skin healthy is to protect it when you're outdoors. Wear a sunscreen with an SPF of at least 15 that protects against both UVA and UVB rays, a hat with a brim and protective clothing, says the American Academy of Dermatology (AAD). Limit your time in the sun, particularly between 10 a.m. and 3 p.m.

Even with the best protection, however, our skin changes as we grow older. It becomes drier and more wrinkled. It loses its ability to stretch, and becomes thinner and less plump looking. Gravity also weighs in, dragging skin downward and causing it to sag.

Dry skin that flakes and itches can be treated with a moisturizer just after a bath or shower, while your skin is still damp, says the AAD. And even sun-damaged skin can benefit from a layer of sunscreen whenever you venture outside.