The subcutaneous layer is the deepest skin layer. It protects a person’s body and keeps it warm. This layer also provides insulation and protection for vital tissues such as muscles, bones, and organs.

This article looks at subcutaneous tissue, its functions, and conditions that can affect this essential skin layer.

Subcutaneous tissue is the deepest skin layer that lies closest to the muscle. This layer has other names, including superficial fascia, hypodermis, subcutis, and tela subcutanea.

The skin consists of layers called the epidermis, dermis, and hypodermis. The epidermis is the outermost layer, and the hypodermis, or subcutaneous layer, is the innermost layer.

The subcutaneous layer consists mainly of fat. The fat forms a layer that insulates the body from cold and helps absorb shock and damage to the internal organs. It also provides structural support for the skin.

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The skin is made up of multiple layers: the epidermis, the dermis, and the subcutaneous layer, which includes fat and important connective tissue.

The body stores fat in the subcutaneous layer. Other components include collagen-rich connective tissue and a network of blood vessels and nerves.

In the body’s abdominal area, which often has more fat, the subcutaneous layer reaches up to 3 centimeters in depth. The thickness depends on someone’s overall body fat composition.

In other areas, such as the eyelids, the subcutaneous layer has no fat and may be as thin as 1 millimeter.

The crucial functions of the subcutaneous layer are due to the significant amount of fat it holds. These functions include:


The subcutaneous layer consists primarily of fat, allowing it to act as the body’s insulator. It regulates the body’s internal temperature independent of the surrounding environment.


The blood vessels in the hypodermis dilate to cool the body down. When blood vessels dilate, they open up or enlarge, allowing more blood to flow into the area. The blood flows away from warmer areas of the body toward cooler regions. The heat radiates away from the body into the environment and cools the body down.

Shock absorption

Besides insulation, the large proportion of fat in the subcutaneous layer also helps with shock absorption. When someone falls or experiences an impact, the fat layer limits the damage to the body’s bones and internal organs.

Structural support

The subcutaneous layer connects the skin with the fibrous tissue of the bones and muscles underneath.

Energy reserve

The body can convert fat stored in the subcutaneous layer to energy if it needs an energy boost.

The subcutaneous layer also produces hormones such as leptin. These hormones send a signal to the body to tell it that it has eaten enough, which helps regulate energy.

Subcutaneous fat is the fat located in the subcutaneous layer. Adipocytes, or fat cells, hold the fat in specialized connective tissue called adipose tissue.

The rest of the body’s fat stores reside in the spaces surrounding organs such as the liver and intestines. This fat is called visceral fat.

A subcutaneous injection is an effective method of injecting medications. People use injection sites on the outer surface of the upper arm, top of the thigh, and the area of the abdomen surrounding the belly button to administer subcutaneous injections.

Anyone administering a subcutaneous injection must avoid placing the needle into the muscle.

Injecting into the subcutaneous layer allows the body to absorb the drug slowly. The slow absorption rate is because compared with muscle, the subcutaneous tissue has far fewer blood vessels. Any substance injected into this layer is absorbed far slower than if someone injected it into the muscle.

A slower absorption rate is beneficial for drugs that require continuous absorption, including:

  • allergy shots
  • blood thinners such as heparin
  • epinephrine
  • fertility drugs
  • insulin
  • morphine

Any medicine injected using the subcutaneous route must be a water-soluble, non-irritant drug administered in small quantities of up to 2 milliliters.

Subcutaneous injections have some drawbacks. People may experience abscesses, which are areas of pus under the skin. Anyone who needs frequent injections may experience an accumulation of fat under the skin called lipohypertrophy. People can avoid this by varying the injection site, as it typically happens when an individual has multiple injections in the same area.

Anything that penetrates the upper layers of skin can damage the subcutaneous layer. As the subcutaneous layer is the deepest skin layer, conditions that damage it can sometimes be severe.


Burns have different classifications according to how deeply they penetrate. The two classifications of burns that affect the subcutaneous layer are third degree and fourth degree burns.

Third degree burns destroy the entire epidermis and dermis and may impact the subcutaneous tissue. These burn sites may appear either white or blackened.

Fourth degree burns enter the subcutaneous layer and may go even deeper. These types of burns may involve the bones and muscles. Since this burn type destroys all the nerve endings in the subcutaneous layer, a person does not have feeling at the burn site.


An abscess is a pocket of pus that can form anywhere in the body, often in the subcutaneous layer of skin. If a germ enters the skin, the person’s immune system attempts to contain it, and white blood cells (WBCs) flood into the area. Pus forms from fluid, WBCs, debris, and dead bacteria. The surrounding area becomes swollen, inflamed, and painful.

Pressure ulcers

If someone has prolonged pressure on their skin due to lying in bed or using a wheelchair, they could develop a pressure ulcer. These skin injuries, also called pressure sores or bedsores, can affect the skin and potentially the subcutaneous layer if they are severe.


People can develop a tumor, such as a sarcoma, in the subcutaneous layer if there is an uncontrolled growth of cells.

Unlike many other types of tumors, people can easily see these masses, and doctors can examine them to see how firm and mobile they are, which helps with diagnosis. These tumors can be benign or malignant.


Panniculitis is an umbrella term for a variety of diseases concerning subcutaneous tissue. The signs of panniculitis include inflammation in the subcutaneous layer and possible scarring of the subcutaneous tissue. This condition is most often associated with autoimmune disorders. It can also be caused by infection and trauma.

The subcutaneous layer is located underneath the dermis and is one of the three layers of the skin. It is the deepest skin layer, composed of fat cells, collagen, blood vessels, and nerves.

The subcutaneous layer has many functions, including insulation, thermoregulation, shock absorption, structural support, and energy storage.

Possible damage to the subcutaneous layer includes third or fourth degree burns, abscesses, pressure ulcers, tumors, and panniculitis.