The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, or superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and macrophages. The subcutaneous tissue is derived from the mesoderm, but unlike the dermis, it is not derived from the mesoderm's dermatome region. It consists primarily of loose connective tissue and contains larger blood vessels and nerves than those found in the dermis. It is a major site of fat storage in the body.

In arthropods, a hypodermis can refer to an epidermal layer of cells that secretes the chitinous cuticle. The term also refers to a layer of cells lying immediately below the epidermis of plants.

Structure

  • Fibrous bands anchoring the skin to the deep fascia
  • Cutaneous nerves
  • Bursae, in the space overlying joints in order to facilitate smooth passage of overlying skin
  • Fine, flat sheets of muscle, in certain locations, including the scalp, face, hand, nipple, and scrotum, called the panniculus carnosus

The hypodermis forms an important insulating layer and/or food store in some animals, such as whales and hibernating mammals.

In some plants, the hypodermis is a layer of cells immediately below the epidermis of leaves. It is often mechanically strengthened, for example, in pine leaves, forming an extra protective layer or a water storage tissue.

=== Subcutaneous fat ===<!-- This Anchor tag serves to provide a permanent target for incoming section links. Please do not move it out of the section heading, even though it disrupts edit summary generation (you can manually fix the edit summary before saving your changes). Please do not modify it, even if you modify the section title. See Template:Anchor for details. (This text: Template:Anchor comment) -->

right|thumb|alt=Two computed tomography images of a horizontal section of the mid-abdominal region; one from a normal-weight individual and the other from an obese person. In both, the bony structures and organs appear similar. The primary difference is that in the normal-weight person, there is little subcutaneous fat, and the obese person shows substantially subcutaneous fat.|Cross-sections of the torso of a person of normal weight (left) and an obese person (right), taken by [[Computed tomography|CT scan. Note the 3.6&nbsp;cm (1.4&nbsp;inches) of subcutaneous fat on the obese person.]]

Subcutaneous fat is the most widely distributed subcutaneous tissue layer.

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