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."

Bursitis

Bursitis is the inflammation or irritation of the bursa. The bursa is a sac filled with lubricating fluid, located between tissues such as bone, muscle, tendons, and skin, that decreases rubbing, friction, and irritation. Bursitis is most often caused by repetitive, minor impact on the area, or from a sudden, more serious injury. Age also plays a role. As tendons age they are able to tolerate stress less, are less elastic, and are easier to tear.