In zootomy and dermatology, skin is an organ of the integumentary system; which is composed of a layer of tissues protect underlying muscles and organs. Skin is used for insulation, vitamin D and B production although people with darker skintone produce more vitamin B than D and people with lighter skin tones produce more vitamin D than B in dramatically different proportions. Hence, in there is Rahitism, as lack of vitamin D in the organism, sensation, and excretion .Skin on creatures regularly subjected to sunlight have pigmentation which absorbs the potentially dangerous radiation contained therein. Human skin pigmentation across populations in a visually dramatic manner. This has sometimes led to the classification of people(s) on the basis of skin color. See the article on human skin color for more information.

Mammalian skin often contains hairs, which in sufficient density is called fur. The hair mainly serves augment the insulation the skin provides. On some animals skin is very hard and thick, and be processed to create leather.Damaged skin will try to heal by forming scar tissue, often giving rise to discoloration and depigmentation of the skin.

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 homo , the skin has a surface area of between 1.5-2.0most of it is between 1-2 mm thick. The average square inch of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.The skin on a person's face is seen by people that person interacts with. For some people, therefore, facial skin care is of particular importance, and they n use cosmetics to deal with the appearance of the face and condition of the skin, such as those for pore control and black head cleansing.

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 . 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 is made up of loose connective tissue and elastin. The main cell types fibroblasts, macrophages and adipocytes . Fat serves as padding and insulation for the body
The skin must be regularly cleaned. Unless enough care is taken it will become cracked or inflamed. The unclean skin favors the development of pathogenic organisms. The constantly peeling off dead cells of the epidermis mix with the secretions 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 begins to decompose emitting unpleasant foul smell. Functions of the skin are

Layers
Skin is composed of the epidermis and the dermis. Below these layers lies the hypodermis, which is not usually classified as a layer of skin.The outermost epidermis is made up 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 which make up the epidermis are keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further subdivided into the following 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 and become filled with keratin. eventually reach the corneum and become sloughed off. 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 linkedarteriole 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 is made up of loose connective tissue otherwise called areolar connective tissue - collagen, elastin and reticular fibres are present. Erector muscles, ed between the hair papilla epidermis, can contract, resulting in the hair fibre pulled upright and consequentially goose bumps. The main cell types are fibroblasts, adipocytes 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 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 . The reticular layer is composed of irregularly arranged fibres 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 is made up of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes . Fat serves as padding and insulation for the body

The skin must be regularly cleaned. Unless enough care is taken it will become cracked or inflamed. The unclean skin favors the development of pathogenic organisms. The constantly peeling off dead cells of the epidermis mix with the secretions sweat and sebaceous glands and the dust found on the skin to form a filthy layer on its surface. If not washed awaybegins to decompose emitting unpleasant foul smell. Functions of the skin are disturbed when dirty and it becomeseasily 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 air play an important role in keeping the skin healthy.