Skin, besides its main role to cover the body, is an organ (the largest!) with a vital activity as well as other internal organs like liver or heart.
   Skin color varies according to sex, age, race and region. At young age, skin has a lighter, children and young women have lighter and thinner skin than adults and the elderly.

Photo by Mikeyloveswomen

   Skin colors are:
• White (because of the epidermis keratohialin);
• Yellow (due to the stratum corneum);
• Red (thanks to the blood of the dermis);
• Brown (due to melanin, the pigment in skin);

   Skin has tiny holes (pores) through which sweat, sebaceous and mammary glands drain them secretions: sweat, sebum and milk. Depending on the amount of this physiological secretions skin can be fatter or softer.

   Skin has three layers, from outside to inside: epidermis, dermis and hypodermis.

                     Epidermis is the peripheral (outer) layer composed of cells arranged in three layers.
  -Stratum Germinativum (deepest layer) composed of keratinocytes (which are designed to permanently renew the cells above) and melanocytes (forming melanin pigment in skin).
  -Stratum Spinosum, the filamentous layer that forms the largest part of the epidermis and consists of several rows of cells from the basal layer, nerve endings and Langerhans cells (which have an immunological role).
  -Stratum granulosum (granular layer) composed of 1-5 rows of cells whose cytoplasm contains important amount of keratohyalin.
  -Stratum lucidum is a transparent layer, clear, under the Stratum Corneum. It consists of small cells, through which light enters.
  -Stratum Corneum composed of epithelial cells has a protective role and that regenerates itself. It is the top layer of skin. Cells of this layer contain keratin, a protein that keeps the skin's moisture level.
  -Exfoliative Layer composed of dead cells that are replaced by formation of new cells. With age, this process of regeneration decreases in intensity leading to loss the freshness of skin.
   With age, the epidermis becomes thinner, leading to wrinkles.

                    Dermis is a connective tissue composed of fibers, cells and ground substance. It represents approximately 90% of skin thickness and is composed of two layers:
  - Stratum papillare (superficial dermis, thinner) contains an arrangement of collagen fibers
  - Stratum reticulare (dermis itself, thicker) contains collagenous fiber bundles arranged parallel to the surface of the skin.
   Fibers of dermis (connective, reticular and elastic) form a network interspersed with cells that are of two kinds: fixed (fibrocytes, mast cells, plasma cells, fibroblasts and pigmentation) and migratory (lymphocytes, monocytes and granulocytes). Fibroblast is to produce collagen fibers. Fibers and cells are covered by a homogeneous, acidophilous, gelatinous and amorphous basic substance. Dermis also contains a network of lymphatic blood vessels and nerve endings system. Sweat and sebaceous glands in the dermis are designed to protect against infections by forming an acidic film, composed of sebum and water. Skin pH (acidity level) is between 5 and 6.
   Collagen and elastin fibers contained in the dermis are designed to maintain the skin healthy. With the age they deteriorate leading to wrinkles.

                   Hypodermis, the last layer of skin is composed of fat and adipose tissue and serves to protect internal organs. With age, adipose tissue becomes thinner leading to skin drooping.