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."

Vitiligo

Vitiligo is a condition in which your skin loses melanin, the pigment that determines the color of your skin, hair and eyes. Vitiligo occurs when the cells that produce melanin die or no longer form melanin, causing slowly enlarging white patches of irregular shapes to appear on your skin. Vitiligo affects all races, but may be more noticeable in people with darker skin. Vitiligo usually starts as small areas of pigment loss that spread with time. There is no cure for vitiligo. The goal of treatment is to stop or slow the progression of pigment loss and, if you desire, attempt to return some color to your skin.