The medical term that describes the area underneath the skin is "subcutaneous tissue." This area is also called the hypoderm, the subcutis, the hypodermis and the superficial fascia. Subcutaneous tissue is sometimes considered the lowest layer of the integumentary system, which lies above deeper tissues such as muscles and nerves.
Subcutaneous tissue contains blood vessels, lymphatic vessels, fat, hair follicle roots, collagen and elastin fibers, Ruffini endings (bulbous corpuscles), Pacinian corpuscles (Lamellar corpuscles), hair follicle roots, sweat glands, and mast cells. The main component of subcutaneous tissue is fat cells, or adipocytes, which together make up adipose tissue, or subcutaneous fat.