Skin components

Skin has pigmentation, or melanin, provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation (UV) in sunlight. It also contains DNA-repair enzymes that help 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 led to the classification of people(s) on the basis of 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 and is often subject to osmosis. A frog sitting in an anesthetic solution could quickly go to sleep.

The skin is often known as the largest organ of the human body. This applies to exterior surface, as it covers the body, appearing to have the largest surface area of all the organs. For the average adult human, the skin has a surface area of between 1.5-2.0 square meters (16.1-21.5 sq ft.), most of it is between 2-3 mm (0.10 inch) thick. The average square inch (6.5 cm²) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.

Skin Texture

Skin texture is a result of smoothness of the skin's surface, hydration of the skin, and the collagen, elastin and glycosaminoglycan content of the skin. All of these properties are affected by hormones, diet, skin care products, and various cosmetic procedures. In addition, there are great treatments for oily skin, dry skin, rough skin and yellow "sallowed" skin. You must be evaluated by one of our doctors in order to form a regimen specific to your skin's needs.

Reticular region

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.

Microorganisms like Staphylococcus epidermidis colonize the skin surface. The density of skin flora depends on region of the skin. The disinfected skin surface gets recolonized from bacteria residing in the deeper areas of the hair follicle, gut and urogenital openings.

Variability in skin tone

Individuals with ancestors from different parts of the world can have highly visible differences in skin pigmentation. Individuals with Sub-Saharan African ancestry (black people) tend towards darker skin, while those of Northern European descent (white people) have paler skin. Between these extremes are individuals of Asian, South-East Asian, Native American, Middle Eastern, Polynesian and Melanesian descent.

The skin of black people has more variation in color from one part of the body to another than does the skin of other racial groups, particularly the palms of the hands and soles of the feet. Part of this is the result of the variations in the thickness of the skin or different parts of the body. The thicker the skin, the more layers of cell with melanin in them, and the darker the color. In addition, these parts of the body do not have melanin-producing cells.

Darker skin hinders UV A rays from penetrating. Since vitamin B folats are degraded by UV A and vitamin D is synthesized different skin tones are more likely to produce different vitamin deficiencies.

Aging

As skin ages, it becomes thinner and more easily damaged. Intensifying this effect is the decreasing ability of skin to heal itself as a person ages.

Skin aging is caused by the fall in elasticity. Aging skin also receives less blood flow and lower gland activity.

Hygiene

Unclean skin favors the development of pathogenic organisms – the dead cells that continually slough off 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 slurry of sweat and sebaceous secretions mixed with dirt and dead skin is decomposed by bacterial flora, producing a foul smell. Functions of the skin are disturbed when it is excessively dirty; it becomes more easily damaged, the release of antibacterial compounds decreases, and 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.

The skin supports its own ecosystems of microorganisms, including yeasts and bacteria, which cannot be removed by any amount of cleaning. Estimates place the number of individual bacteria on the surface of one square inch (6.5 square cm) of human skin at 50 million though this figure varies greatly over the average 20 feet² (1.9 m²) of human skin. Oily surfaces, such as the face, may contain over 500 million bacteria per square inch (6.5 cm²). Despite these vast quantities, all of the bacteria found on the skin's surface would fit into a volume the size of a pea. In general, the microorganisms keep one another in check and are part of a healthy skin. When the balance is disturbed, there may be an overgrowth and infection, such as when antibiotics kill microbes, resulting in an overgrowth of yeast. The skin is continuous with the inner epithelial lining of the body at the orifices, each of which supports its own complement of microbes.

Oily skin is caused by over-active glands, that produce a substance called sebum, a naturally healthy skin lubricant. When the skin produces excessive sebum, it becomes heavy and thick in texture. Oily skin is typified by shininess, blemishes and pimples. The oily-skin type is not necessarily bad, since such skin is less prone to wrinkling, or other signs of aging, because the oil helps to keep needed moisture locked into the epidermis (outermost layer of skin).

The negative aspect of the oily-skin type is that oily complexions are especially susceptible to clogged pores, blackheads, and buildup of dead skin cells on the surface of the skin. Oily skin can be sallow and rough in texture and tends to have large, clearly visible pores everywhere, except around the eyes and neck.

Functions

1. Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system.
2. Sensation: contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury; see somatosensory system and haptics.
3. Heat regulation: the skin contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. Dilated blood vessels increase perfusion and heat loss while constricted vessels greatly reduce cutaneous blood flow and conserve heat. Erector pili muscles are significant in animals.
4. Control of evaporation: the skin provides a relatively dry and impermeable barrier to fluid loss. Loss of this function contributes to the massive fluid loss in burns.
5. Aesthetics and communication: others see our skin and can assess our mood, physical state and attractiveness.
6. Storage and synthesis: acts as a storage center for lipids and water, as well as a means of synthesis of vitamin D by action of UV on certain parts of the skin.
7. Excretion: sweat contains urea, however its concentration is 1/130th that of urine, hence excretion by sweating is at most a secondary function to temperature regulation.
8. Absorption: Oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts, some animals using their skin for their sole respiration organ. In addition, medicine can be administered through the skin, by ointments or by means of adhesive patch, such as the nicotine patch or iontophoresis. The skin is an important site of transport in many other organisms.
9. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.

Skin

The skin is the outer covering of living tissue of an animal. It is the largest organ of the integumentary system made up of multiple layers of epithelial tissues, and guards the underlying muscles, bones, ligaments, internal organs. The adjective cutaneous literally means "of the skin" (from Latin cutis, skin).

Because it interfaces with the environment, skin plays a very important role in protecting (the body) against pathogens. Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates. Severely damaged skin will try to heal by forming scar tissue. This is often discolored and depigmented.

In humans, skin pigmentation varies among populations, and skin type can range from dry to oily.