The Skinny on Skin

Skin is your body's largest organ. It protects you against bacteria, viruses, dirt, wind, heat, and cold. It also can serve as a "window" to the body, alerting doctors when something is wrong internally.

Your skin needs a steady supply of new cells to protect your 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.


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 you against the sun's ultraviolet (UV) rays.


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 30 that is broad spectrum (protects against both UVA and UVB rays), a hat with a brim, and protective clothing. Limit your time in the sun, particularly between 10 a.m. and 2 p.m. Keep in mind that even sun-damaged skin can benefit from a layer of sunscreen whenever you venture outdoors.

Even with the best protection, however, your skin changes as you grow older. It tends to become drier and more wrinkled. It loses its ability to stretch, becomes thinner, and less plump looking. Gravity also plays a role, dragging skin downward and causing it to sag.

You can treat dry skin that flakes and itches with a moisturizer that you apply just after a bath or shower, while your skin is still damp. Avoid using hot water. It can remove the natural oils from your skin. Also, limit time in the shower or bathtub to under 10 minutes. You may consider using a humidifier to moisturize the air in your home.