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.

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 outermost epidermis is consists of stratified squamous epithelium with an underlying basement membrane. It contains no blood vessels, and is nourished by diffusion from the dermis. The main type of cells which make up the epidermis are keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum, granulosum, spinosum, basale. Cells are formed through mitosis at the innermost layers. They move up the strata changing shape and composition as they differentiate, inducing expression of new types of keratin genes. They eventually reach the corneum and become sloughed off (desquamation). This process is called keratinization and takes place within about 30 days. This layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out.

Blood capillaries are found beneath the epidermis, and are linked to an arteriole and a venule. Arterial shunt vessels may bypass the network in ears, the nose and fingertips.

The dermis lies below the epidermis and contains a number of structures including blood vessels, nerves, hair follicles, smooth muscle, glands and lymphatic tissue. It consists of loose connective tissue otherwise called areolar connective tissue - collagen, elastin and reticular fibres are present. Erector muscles, attached between the hair papilla and epidermis, can contract, resulting in the hair fibre pulled upright and consequentially goose bumps.

The dermis can be split into the papillary and reticular layers. The papillary layer is outermost and extends into the dermis to supply it with vessels. It is composed of loosely arranged fibres. Papillary ridges make up the lines of the hands. The reticular layer is more dense and is continuous with the hypodermis. It contains the bulk of the structures (such as sweat glands). The reticular layer is composed of irregularly arranged fibres and resists stretching.

The hypodermis is not part of the skin, and lies below the dermis. Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat). Fat serves as padding and insulation for the body.

Skin can be dividided into thick and thin types. Thick skin is present on the soles of the feet and the palms of the hands. It has a larger stratum corneum with a higher keratin content. Thick skin does not grow hair; its purpose is to help grip. Thin skin is present on the bulk of the body and has a smaller stratum corneum and fewer papillae ridges. It has hair and is softer and more elastic. The characteristics of the skin, including sensory nerve density and the type of hair, vary with location on the body.

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.

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.

If you take care of your skin, your skin will take care of you! But with all of the lotions, creams, and potions on the market, it can be difficult to know which product will work for you. Many products claim to remove wrinkles or heal dry skin. Others claim to contain expensive ingredients that they say will improve the effects of the product.

The first step to taking care of your skin is preventing damage. Sun, wind, pollutants, and simply aging can degrade the condition of your skin. Common complaints include dry and itchy skin, wrinkles, sagging, color changes, and age spots. There are steps that you can take to keep you skin looking and feeling its best.

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.

Unless your skin is very oily, you will want to use a moisturizer everyday to keep your skin hydrated and healthy. Your skin needs moisturizer all year long as both the indoor winter heat, and summer sun can be equally damaging to your skin.

Why is it that practically everyone in the middle class to the upper levels of demographics in any country are worried about getting wrinkles? Maybe it is the fear of getting old or looking old, or the wanting to look socially acceptable, or just plain vanity. We all have our own reasons. But whatever it is, everyone is united in wanting to solve this age old problem. However, in the first place, do we even have any idea about what actually causes these dreaded wrinkles? It's highly probable that we don't. The most important factor in finding a solution to any problem is finding out the root cause of it.

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".

One less painful procedure is the particle skin resurfacing procedure. The process is removes the outer layer of skin in a highly controlled manner. Because of its preciseness, it is practically painless. By repeating this procedure a number of times, the younger skin moves to the surface, thus promoting visible changes in the skin's texture, color and appearance. The benefits of this skin resurfacing procedure are that it causes very little pain or discomfort, no recuperative period is needed, there is minimal risk, it can be used for all skin types, and no anesthesia is required.

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.

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.

Definitions and terms

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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