subcutis

Subcutis, also called the hypodermis or superficial fascia, is the layer of tissue directly beneath the dermis. It is part of the integumentary system and, in humans, forms the boundary between the skin and deeper tissues such as underlying fascia and muscle.

Microanatomy: It consists mainly of loose connective tissue and adipose tissue; adipocytes form lobules separated by fibrous septa; it contains blood vessels, lymphatics, and cutaneous nerves that supply the skin; in many mammals a layer called panniculus adiposus is present.

Functions: Provides insulation to conserve body heat, stores energy in the form of fat, cushions deeper structures against trauma, and serves as a conduit for nerves and vessels; in some animals there is a panniculus carnosus—a muscle layer that moves the skin, but not typically in humans.

Clinical and anatomical notes: Subcutis is sometimes used synonymously with the hypodermis; thickness varies with age, sex, body fat, and site; subcutaneous injections are delivered into this layer; pathologies include lipomas, cellulitis, panniculitis, edema, and obesity-related changes; imaging can assess subcutis health.