What is the function of skin?

The outermost layer of your skin, the epidermis, is the thin, tough part of your body that acts like a protective shell. Because they're also the first to encounter damage, the cells of the epidermis are constantly renewing themselves, with dead skin cells falling off by the tens of thousands each minute.

One of the most basic functions of the epidermis is waterproofing [source: The Merck Manuals]. Have you ever wondered why your body never absorbs water when you get caught in the rain or take a shower? That's because the epidermis contains a layer of cells called stratum corneum, which are packed tightly to protect your body against the absorption of harmful substances. This layer also protects your body from losing too much water [source: P&G].

When the epidermis is healthy, it protects the body from bacteria, viruses, infection and other unwanted substances [source: The Merck Manuals]. Protection starts with the natural layer of oil that appears on the outermost surface of the skin, providing the first barrier of protection. The stratum corneum also protects against the invasion of foreign substances. The epidermis also contains Langerhans cells, specialized cells that identify harmful substances and take them to white blood cells to be neutralized [source: P&G].

The epidermis layer also contains melanin, the skin pigmentation that helps filter dangerous ultraviolet (UV) rays and prevents the skin from absorbing them, which can cause wrinkles and skin cancer. However, studies have shown that the epidermis layer can't completely stop this type of damage, so it's beneficial to protect yourself with sunscreen, protective clothing and minimal sun exposure [source: The Merck Manuals].

Now that you know how your skin protects you, are you ready to find out what goes on under the surface of your skin? To find out how your skin regulates your body temperature, go to out the next page.

The dermis is the layer of skin under the epidermis, and it's made up mostly of soft tissue such as collagen, elastin and fibrillin -- tissues that make your skin elastic and flexible yet strong and structurally firm. The dermis layer also contains blood vessels, hair follicles, nerve endings, oil glands and sweat glands. It's the latter of these that makes the dermis so important to heat regulation. The dermis controls body temperature through the production of sweat and the control of evaporation -- a process known as insensible perspiration. Basically, the sweat glands of the dermis secrete sweat, which then evaporates on the surface of the skin. Because evaporation requires heat to work, the process of evaporating sweat actually helps to lower the temperature of your skin [source: P&G].

The dermis also regulates temperature by controlling red blood cells. When the body is cold, the red blood cells of the dermis contract, which helps to retain internal body temperature. When the body is hot, the red blood cells expand, allowing heat to be released through the surface of the skin [source: The Merck Manuals].

The subcutaneous layer is made up of fat cells and fibrous tissue [source: The Merck Manuals]. Like the dermis, the subcutaneous layer helps to regulate body temperature. In this case, however, it provides insulation against the absorption of cold and the loss of heat [source: P&G].

The skin doesn't stop there with protection and regulation. It also provides you with one of your most useful senses -- the sense of touch. To learn more about how the skin influences your senses, read the next page.

The dermis serves an important role in regulating body temperature. But it also performs another critical function: It contains the nerve endings that give you your sense of touch [source: The Merck Manuals].

The nerve endings in the dermis identify five different kinds of sensations: heat, cold, pressure, pain and contact. This is because there are millions of nerve endings in the dermis, with higher concentrations in certain areas of the body [source: Medindia]. Places where skin is thinner often have either a greater concentration of nerve endings or less protection, making them more sensitive.

Injuries to the skin can adversely affect your experience of touch. For example, even a minor burn can be quite painful, because it affects the nerve endings in your skin. Usually a first- or second-degree burn can continue to hurt even after it has developed scar tissue, because the nerve endings are continuing to react to the injury. What's even more dangerous, however, is when you don't feel any pain from a burn -- that means that you've suffered from a third-degree burn, which penetrates the dermis. The reason you don't feel pain with a third-degree burn is because the nerve endings in the dermis have actually been destroyed [source: Wolfe].

For lots more information about the function of skin, see the links on the next page.