Skin Care Basics -- Anatomy of the Skin
Skin is the body's largest organ. It's made up of three layers: the epidermis, the dermis, and the hypodermis.
Epidermis
The epidermis is the thin, protective outer layer of skin. It is made of five distinct sub-layers. About 90% to 95% of the epidermis is made of keratinocytes, a type of skin cell. The epidermis renews itself every month or so, so the body is constantly shedding dead skin cells from this layer. New cells arise from the deepest sub-layer of the epidermis and mature as they move toward the surface.
The skin's surface is made of hard, flat dead cells "glued" together by lipids (fats) and proteins secreted by underlying skin cells. Together, these dead cells and fats and proteins form a protective barrier that keeps out environmental factors. Immune cells in the epidermis called Langerhans cells help ward off pathogens as well.
The skin of the epidermis is thinnest on the face and thickest where the most protection from injury and minor trauma is needed, such as on the soles of the feet and on the palms. Cells at the base of the epidermis called melanocytes produce melanin, the pigment that determines skin color and provides some protection against the sun's ultraviolet rays. The epidermis doesn't have a blood supply, so it's nourished by blood vessels in the underlying dermis.
Dermis
The dermis is the middle layer of skin. It is the thickest skin layer and is made up of two sub-layers that contain small blood and lymph vessels, nerves, hair follicles, sweat and oil glands, and nerve receptors to sense touch, temperature, pressure, position, and pain.
Dermal cells called fibroblasts manufacture collagen, a type of connective tissue that comprises about 95% of the dermis. Collagen gives skin its strength and resilience. Fibroblasts also manufacture elastin, a protein that makes skin flexible. Breakdown of collagen and elastin contributes to wrinkling.
