Skin

"The skin is the largest organ of the body, with a total area of about 20 square feet. The skin protects us from microbes and the elements, helps regulate body temperature, and permits the sensations of touch, heat, and cold.
Skin has three layers: The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.
The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands.
The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue.
The skin’s color is created by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermis."

Psoriasis

Psoriasis is a common skin disease that affects the life cycle of skin cells. Psoriasis causes cells to build up rapidly on the surface of the skin, forming thick silvery scales and itchy, dry, red patches that are sometimes painful. Psoriasis is a persistent, long-lasting (chronic) disease. You may have periods when your psoriasis symptoms improve or go into remission alternating with times your psoriasis worsens.