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."

Itching sensation

Pain and itch have very different behavioral response patterns. Pain evokes a withdrawal reflex which leads to retraction and therefore a reaction trying to protect an endangered part of the body. Itch creates a scratch reflex which draws one to the affected skin site. For example, responding to a local itch sensation is an effective way to remove insects on the skin. Scratching has traditionally been regarded as a way to relieve oneself by reducing the annoying itch sensation. However there are hedonic aspects of scratching as one would find noxious scratching highly pleasurable. This can be problematic with chronic itch patients, such as ones with atopic dermatitis, who may scratch affected spots until it no longer produces a pleasant or painful sensation instead of when the itch sensation disappears.