In zootomy and dermatology, skin is an organ of the integumentary system composed of a layer of tissues that protect underlying muscles and organs. As the interface with the surroundings, it plays the most important role in protecting against pathogens. Its other main functions are insulation and temperature regulation, sensation and vitamin D and B synthesis.

Skin has pigmentation, provided by melanocytes, which absorbs some of the potentially dangerous radiation in sunlight. It also contains DNA repair enzymes which reverse UV damage, and people who lack the genes for these enzymes suffer high rates of skin cancer. One form predominantly produced by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be deadly. Human skin pigmentation varies among populations in a striking manner. This has sometimes led to the classification of people on the basis of skin color. See the article on human skin color.

Mammalian skin often contains hairs, which in sufficient density is called fur. The hair mainly serves to augment the insulation the skin provides, but can also serve as a secondary sexual characteristic or as camouflage. On some animals the skin is very hard and thick, and can be processed to create leather. Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough β-keratins. Amphibian skin is not a strong barrier to passage of chemicals. A frog sitting in an anesthetic solution will quickly go to sleep.

The skin is often known as "the largest organ in the human body". This applies to exterior surface, as it covers the body, appearing to have the largest surface area of all the organs. Moreover, it applies to weight, as it weighs more than any single internal organ, accounting for about 15 percent of body weight. For the average adult human, the skin has a surface area of between 1.5-2.0 square metres, most of it is between 2-3 mm thick. The average square inch of skin holds 650 sweat glands, 20 blood vessels, 1000 melanocytes, and more than a thousand nerve endings.

The main cell types of skin are fibroblasts, adipocytes (fat storage) and macrophages. Sebaceous glands are exocrine glands which produce sebum, a mixture of lipids and waxy substances: lubrication, water-proofing, softening and antibactericidal actions are among the many functions of sebum. Sweat glands open up via a duct onto the skin by a pore.

The skin must be regularly cleaned. Unless enough care is taken it will become cracked or inflamed. Unclean skin favors the development of pathogenic organisms.

The constantly peeling off dead cells of the epidermis mix with the secretions of the sweat and sebaceous glands and the dust found on the skin to form a filthy layer on its surface. If not washed away the dirt and dead skin slurry begins to decompose emitting a foul smell.

Functions of the skin are disturbed when it is dirty and it becomes more easily damaged. The release of antibacterial compounds decreases. Dirty skin is more prone to develop infections. Cosmetics should be used carefully because these may cause allergic reactions. Each season requires suitable clothing in order to facilitate the evaporation of the sweat. Sunlight, water and air play an important role in keeping the skin healthy.

In fact, skin care and protection should be an essential part of your health, fitness, and beauty regime. If you take care of your skin, your skin will take care of you! If your stuck in a skin care rut, or if you are just looking to learn a bit more about the basics of skin care, read on to learn more about this important step in your daily activities.

You are never too young or too old to start taking care of your skin. In fact, skin care and protection should be an essential part of your health, fitness, and beauty regime.

Exercise, rest, and good nutrition lay the foundation for beautiful, healthy skin, inside and out. A proper diet is not only good for your overall health, it also helps to ensure that your skin will receive all of the vitamins, minerals, and nutrients that it needs to maintain and repair cells. Drinking purified water is another good way to keep your skin healthy. Water helps to hydrate the skin and move waste and nutrients through the system. It is very effective mixing a teaspoon or capful of Organic Apple Cider Vinegar in with your water. Do not drink Tap Water.

The most important way to care for your skin is to protect it from the damaging rays of the sun. Ultraviolet radiation damages the skin and can lead to wrinkles, premature aging, age spots, and cancer. Take extra precautions to make sure your skin is not exposed to the sun's rays. Use a natural sunscreen, or a moisturizer that contains sunscreen (at least SPF 15) everyday. Your skin does need some sunlight 10-15 minutes of direct exposure daily.

Dry skin is very common, especially with age. Older skin has fewer sweat and oil glands than younger skin. Dry skin may be caused by frequent baths, certain cosmetics or medications. But whatever the cause, there are ways to alleviate the itchiness associated with it. Avoid using harsh soaps when bathing, and if possible, cut back on the number of baths or showers each week. A sponge bath with warm water may help to clean and revive skin without stripping the skin of its valuable moisturizers.

A skin care routine does not have to be elaborate in order to be effective. But you should develop some kind of skin care routine based on your skin type, daily activities, and nutritional needs so that you can be sure you are taking the very best care of your skin. Following a daily skin care regime will also allow you to more closely evaluate your skin for abnormalities.

Use a natural sunscreen when possible, regardless of whether or not you plan on spending much time in the sun. The sun's rays are very damaging and if you get in the habit of applying sunscreen everyday, you will never be left without protection. The suns most beneficial rays occur at sunrise and sunset.

As we age, our body undergoes various changes, and so does our skin. In our skin, we have tissues known as collagen and elastin. These tissues are mainly responsible for making our skin firm and stretchable. As we grow older, the amount of collagen and elastin in our skin naturally diminishes. As a result, our skin becomes less elastic and weaker, thus creating "wrinkles".

The important thing to remember when seeking out treatment for your wrinkles is to know first how your body can possibly react to the treatment. Get in touch with a skin doctor for things that you are not sure of, but are contemplating on trying out.

While it is true that physical beauty is just skin deep, it is still no reason why people, particularly women, should disregard basic skin care. Since the skin is our outermost layer, it is exposed to the harsh elements of the environment. And because it is not uncommon for people to base judgments from our cover, with the face being the first thing they look at, it is only proper that we go to great lengths to keep our skin looking clean and fresh.

There are a lot of skin care products in the market today. Unlike before when a normal bar of soap was used for skin cleansing, cosmetic companies are now producing a wide variety of skin care treatments that can address various skin concerns. However, there are cases when treatments need to be more aggressive, especially for those who have aging or blemished skin. Most, if not all, of the over-the-counter products are topical in nature, meaning it only affects the epidermis or the outer layer of the skin. Aging or blemished skin needs to be treated down to the root of the problem to see definite changes.

Terms on this page

Acne

• An inflammatory disease of the sebaceous glands and hair follicles of the skin that is marked by the eruption of pimples or pustules, especially on the face.

Bacteria

• Microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles.

Dermis

• The sensitive connective tissue layer of the skin located below the epidermis, containing nerve endings, sweat and sebaceous glands, and blood and lymph vessels.

Epidermis

• The outer, protective, nonvascular layer of the skin of vertebrates, covering the dermis.

Hypodermis

• A subcutaneous layer of loose connective tissue containing a varying number of fat cells.

Pimples

• A small swelling of the skin, usually caused by acne; a papule or pustule.

Ultraviolet radiation

• Invisible electromagnetic radiation between visible violet light and X rays.

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