The skin is the largest organ in the body, comprising about 15% of the body weight. The total skin surface of an adult ranges from 12 to 20 square feet. In terms of chemical composition, the skin is about 70% water, 25% protein and 2% lipids. The remainder includes Trace Minerals, Nucleic Acids, Glycosoaminoglycans, Proteoglycans and numerous other chemicals. The skin is an ever-changing organ that contains many specialized cells and structures. The skin functions as a protective barrier that interfaces with a sometimes-hostile environment. It is also very involved in maintaining the proper temperature for the body to function well. It gathers sensory information from the environment, and plays an active role in the immune system protecting us from disease. Every element within the warmth/airy/watery/solid domains also finds its reflection in the skin. If the skin is a "mirror" of the whole human being, then external skin diseases are mirrors of in­ternal pathological disturbances.

 

Understanding how the skin can function in these many ways starts with understanding the structure of the 3 layers of skin - the Epidermis, Dermis, and Subcutis (subcutaneous tissue).

 

Epidermis:

The epidermis is the outermost layer of the skin, and protects the body from the environment, the total thinkness of the epidermis is usually about 0.5 - 1 mm, the thickness of the epidermis varies in different types of skin; it is only .05 mm thick on the eyelids. The epidermis layer itself is made up of five sublayers that work together to continually rebuild the surface of the skin: Stratum corneum surface is actually composed of dead skin cells that were made at the bottom of this layer and have risen to the top, continuously slough off and are replaced by new ones coming from below.

 

The condition of epdermis determines how "fresh" your skin looks and also how well your skin absorbs and holds moisture. Another significant group of cell in the epidermis are melanocytes, the cells producing melanin, found in the basal layer of the epidermis, responsible for depth of skin color. Langerhans cells in the skin, is the only cells able to 'see' and 'alert' other responding immune cells to initiate a protective response against harmful foreign invaders. "The condition of epdermis determines how "fresh" your skin looks and also how well your skin absorbs and holds moisture".

 

Dermis:

The dermis is the thickest of the three layers of the skin (1.5 to 4 mm thick), making up approximately 90 percent of the thickness of the skin. The main functions of the dermis are to regulate temperature and to supply the epidermis with nutrient-saturated blood. Much of the body’s water supply is stored within the dermis.

 

 

The dermis layer is made up of two sublayers:

The Papillary Layer: The upper, papillary layer, contains a thin arrangement of collagen fibers. The papillary

layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are accomplished with a thin, extensive vascular system that operates similarly to other vascular systems in the body. Constriction and expansion control the amount of blood that flows through the skin and dictate whether body heat is dispelled when the skin is hot or conserved when it is cold.

 

The Reticular Layer:

The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged in parallel to the surface of the skin. The reticular layer is denser than the papillary dermis, and it strengthens the skin, providing structure and elasticity. It also supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.

 

 

The dermis contains the following:

Blood vessels; the blood vessels supply nutrients and oxygen to the skin and take away cell waste and cell products. The blood vessels also transport the vitamin D produced in the skin back to the rest of the body.

 

Lymph vessels; the lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.

 

Hair follicles; the hair follicle is a tube-shaped sheath that surrounds the part of the hair that is under the skin and nourishes the hair.

 

Sebaceous (oil) glands;  sebacious glands, located around hair follicles and can be found everywhere on the body except for the palms of the hands and the soles of the feet, are of particular importance for skin health as they produce sebum, an oily protective substance that lubricates and waterproofs the skin and hair. When sebacious gland produce too little sebum, as is common in older people, the skin becomes excessively dry and more prone to wrinkling. Conversely, overproduction or improper composition of sebum, as is common in adolescents, often leads to acne.

 

Sweat glands; the average person has about 3 million sweat glands. Sweat glands are classified according to two types: Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region. These glands secrete a milky sweat that encourages the growth of the bacteria responsible for body odor.

 

Eccrine glands; are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and reduces skin temperature. These glands can produce up to two liters of sweat an hour, however, they secrete mostly water, which doesn’t encourage the growth of odor-producing bacteria. Fibroblasts: The dermis is held together by a protein called collagen, made by fibroblasts.

 

Fibroblasts are skin cells that give the skin its strength and resilience. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, is the substance that allows the skin to spring back into place when stretched and keeps the skin flexible. (Aging is associated with a loss of fibrous tissue), slower rate of cellular renewal, and a reduced vascular and glandular network. Barrier function that maintains cellular hydration also becomes impaired. The subcutaneous tissue (hypodermis) flattens, particularly in the face, hands and feet.

 

Nerve Endings:

The dermis layer also contains pain and touch receptors that transmit sensations of pain, itch, pressure and information regarding temperature to the brain for interpretation. If necessary, shivering (involuntary contraction and relaxation of muscles) is triggered, generating body heat. The dermis is the layer responsible for the skin's structural integrity, elasticity and resilience. Wrinkles arise and develop in the dermis.

 

Subcutis (Subcutaneous tissue):

The Subcutis is the deepest layer of skin, and consists of a network of collagen and fat cells, and is responsible for connected muscle tissue, bone, and skin. Subcutis fat acts as a shock absorber and heat insulator, protecting underlying tissues from cold and mechanical trauma, and protecting the inner organs. It also stores fat as an energy reserve for the body, the thickness of the subcutis layer varies throughout the body and from person to person. Sweat glands and minute muscles attached to hair follicles originate in subcutaneous tissue. The loss of subcutaneous tissue, often occurring with age, leads to facial sag and accentuates wrinkles.