What Is Subcutaneous Tissue?

The subcutaneous tissue consists primarily of fat and serves several vital functions. It insulates the body, regulates temperature and helps absorb shock and damage. It also provides support for muscles, blood vessels and nerves.


A foreign body in the subcutaneous tissue can cause secondary soft-tissue inflammation resulting in granuloma, abscess or pus formation (Fig. 16a). US depicts these lesions as elongated fluid collections overlying the normal straight echogenic appearance of fascia.


Insulation is the ability to slow or prevent the flow of heat from warmer areas to colder ones. In humans, the subcutaneous layer of fat acts as an insulator, protecting underlying muscle and bone from shock and extreme temperature changes. It also acts as a source of energy, storing the calories we consume.

The thin layer of fat found in the subcutaneous tissue is made up of clusters or sheets of lipid-filled cells called adipocytes. Its thickness varies throughout the body and from person to person, but it helps to regulate your body temperature, protects the underlying muscle and bones, and serves as an energy reserve.

It also provides a buffer to protect the inner layers of your skin, and is a natural shock absorber, helping to reduce the impact of falls or blows. The spongy, resilient layer of fat in the subcutaneous tissue is often described as the “tank top layer” that offers an extra cushion next to your ribcage and sternum when you take a fall.

Since the subcutaneous layer has a limited network of blood vessels, medications injected there are absorbed more slowly than when they’re injected directly into a blood vessel. That makes it an ideal delivery route for vaccines, insulin, and other drugs. Lastly, the subcutaneous layer of fat provides an important physical defense, acting as a barrier between the epidermis and dermis, and preventing the penetration of water or other liquids through the skin.


The subcutaneous layer helps protect the bones, muscles and internal organs from physical damage. The layer also stores fat that can be converted to energy.

When the body senses a small difference between its internal temperature and environmental temperature, sensors in the hypothalamus send signals to the blood vessels in the subcutaneous tissue. These vessels become narrower to decrease the amount of heat they are dumping into the skin. This is called thermoregulatory vasoconstriction.

Once the body is able to regulate its own temperature, it no longer needs to dump heat into the skin. The subcutaneous layer of fat is insulated and keeps the skin close to the body’s core temperature.

The layer also absorbs shock from falls or injuries. It is this function that makes the fatty layer important in limiting the injuries caused to the bones, muscles and organs below. As people age, they begin to lose the extra insulation provided by their subcutaneous layer. This loss of fat and resulting thinner skin puts older people at greater risk for extreme temperatures, and it makes them sweat less, which can lead to dehydration. It can also make it harder for them to maintain their body temperature, and they may suffer from the conditions known as hypothermia and hyperthermia. In addition, the fatty layer makes it easy for some medications to be absorbed into the body.

Shock Absorption

The subcutaneous layer also helps to absorb shock and limit damage to the muscles, bones and internal organs. It contains a large proportion of fat cells (adipose tissue) that act as a cushion against sudden forces like falls and impacts. The body can convert the fat in the subcutaneous layer to energy when needed.

The skin’s three layers are the epidermis, the dermis and the subcutaneous tissue. The epidermis is the outermost layer, and it’s made of overlapping cells that provide protection from the environment. The dermis is the middle layer that consists of sweat glands, blood vessels and connective tissue. And the subcutaneous layer is the deepest, most fatty layer that’s filled with a network of blood vessels and nerves.

The subcutaneous layer provides insulation, thermoregulation, shock absorption and structural support. It also serves as a reservoir of fat that the body can use for fuel when necessary. It is also an important part of the nervous system, providing sensory information to the brain and nerves. For this reason, the subcutaneous tissue is a vital part of your health and well-being. When injected, drugs and medications can be more effectively absorbed from the subcutaneous layer than the gastrointestinal tract. The injection site and patient’s perfusion significantly impact absorption. This is particularly true for salts of poorly soluble bases and acids, or in patients with low perfusion (eg, in shock). For this reason, IM and SC injections should be given only when the patient can comply with the six rights of medication safety.

Structural Support

The fat in the subcutaneous tissue provides structural support for the skin. It also provides a protective barrier against mechanical, thermal and chemical injury, as well as harmful substances like UV radiation. The adipose tissue also stores energy in the form of glycosaminoglycans.

The adipose tissue is surrounded by dense fascia that holds other structures in place, such as the deeper adnexal organs like hair follicles and deep pressure sensors (Ruffini and Paccinian corpuscles). The subcutaneous layer also houses nerves and blood vessels.

Subcutaneous tissue contains a large number of cells that perform many functions, including immunological responses, the regulation of vascular volume and the maintenance of homeostasis. Fibroblasts are the primary cells in this layer, but mast cells and hepatocytes can also be found within the subcutis.

In the past, some anatomists believed that the subcutis was divided into a superficial and deep fascia by a fibrous layer. This layer was called a panniculus adiposus by some English anatomists, textus connectives compactus by French anatomists and straffen bindegewebe by German authors. These layers have since been renamed to the fascia superficialis and fascia profunda, respectively.

The fascia is fairly adherent to the overlying skin and subcutaneous tissue in most regions. This makes it easy for surgeons to surgically separate these tissues. The fascia is held together by the protein laminin, which has five -chains connected to each other by linker regions. Various isoforms of laminin are present in different tissues.