What Is Subcutaneous Tissue?

The subcutaneous tissue (also referred to as superficial fascia or hypodermis) is an important layer of loose connective tissue immediately under the skin. It serves many vital functions, such as providing insulation and water storage.


Contusion trauma may produce subcutaneous fat necrosis. US demonstrates a fluid collection with hyperechoic foci mimicking a tendon gap on physical examination.


The fat that forms this layer is important for padding the body, which protects muscles, bones and organs from physical damage. It also helps to regulate the body’s temperature.

The thickness of this tissue varies by location on the body and differs by gender (see image below). Men tend to accumulate fat around their abdomen and shoulders, while women often have more subcutaneous fat in their hips, thighs and buttocks. The size of adipocytes, which form this tissue, is influenced by diet and nutrition, and a person’s metabolic rate affects how much fat he or she stores.

Like the armor that medieval knights wore, this fat acts as the body’s natural padding, protecting bones, muscles, internal organs and other delicate tissues from damage. It also absorbs shock and prevents the deeper structures from evaporating excessively or cooling due to environmental temperatures in the surrounding environment (thermoregulation).

In addition, this layer helps to transport nutrients throughout the body. It is composed of a network of connective tissue septa and fatty lobules. The septa may be tiny in loose skin or compact when firmly attached to the fascia. In general, the structure of this layer looks like a weblike laminate of fibrous tissue, with each lamella a dense film of collagen and fibrocytes that contains fluid-filled spaces (see image below). In a trauma setting, this tissue can be affected by changes in blood flow, including hemorrhage into fatty lobules, fat necrosis and hematomas.


Soft tissue tumors are a class of malignant (cancerous) growths that can occur in any part of the body and may be painless. They form in the fat, muscles, tendons, blood vessels, lymph vessels and tissue surrounding joints. If a soft tissue tumor is cancerous, it can spread through the bloodstream to other parts of the body where it may develop another tumour (metastasis).

Inflammatory and benign changes in subcutaneous tissue are common. They may be caused by contusion trauma, infection, third or fourth degree burns and traumatic injury to connective tissue. They are commonly seen in the shoulder, arm and thigh. Hemorrhagic changes in the subcutaneous tissues can result in hematomas and abscesses.

Hemorrhagic fatty infiltration is often mistaken for simple edema by US due to the similar hypoechoic appearance of the lobules and the surrounding hyperechoic connective tissue strands of the skin (Fig. 7a). Hemorrhagic changes can also be confused with a neoplasm or other infiltration of the skin by an experienced sonographer.

Benign mass growths in the subcutaneous tissue are more than 10 times more frequent than sarcomas (cancerous growths). They may be round or elliptical in shape, hard or soft to the touch and can grow quickly, causing pain or pressure symptoms such as an abscess. They can be located in any part of the body but are most common in the hands, arms and legs, especially in teenagers and young adults.


Panniculitis is a group of inflammatory disorders affecting the subcutaneous fat. Lesions of this type are characterized by painful, hard bumps under the skin (nodules). The bumps are red or darker in color. They can sometimes become ulcerated. The nodules usually occur on the lower legs or feet, but they can also occur in other parts of the body, such as the abdomen, breasts, face, or buttocks.

The panniculitis can be caused by many things, including infections, injuries, and certain medications. It can cause a variety of symptoms, from pain to fever and other signs. It can spread quickly. If you have any of the signs or symptoms of panniculitis, talk to your doctor.

A biopsy can help determine the cause of your panniculitis. The tissue sample will be sent to a lab to be looked at under a microscope. The results will help your doctor decide how to treat your condition.

The most common form of panniculitis is erythema nodosum (EN). It can be caused by infection, injury, or cold exposure. It affects men and women, but it is more common in older adults. It can also be a sign of other conditions, such as sarcoidosis and lupus. There are two types of panniculitis: septal and lobular. Septal panniculitis mainly affects the connective tissue, while lobular panniculitis mainly involves the fat lobules.


Subcutaneous injections can be used for administering drugs that are needed slowly, such as insulin for diabetes and certain drugs for autoimmune diseases like arthritis. The injection is given into the fatty tissue layer that insulates and regulates body temperature. Because it contains a limited number of blood vessels, medications injected into the subcutaneous tissue are absorbed at a slow rate. The upper arms, abdomen and buttocks are suitable sites (Lynn, 2011).

Before giving a subcutaneous injection, wash hands. Next, wipe the skin with an alcohol wipe and let it dry. Prepare the syringe by opening the cap, removing it, and drawing medication into the syringe with the proper amount according to instructions. Point the needle toward the skin to be injected and then pinch the area gently with the thumb and first finger. This helps to reduce pain and prevent bruising. Insert the needle into the fatty tissue at a 45- to 90-degree angle. Inserting quickly minimizes pain to the patient.

A person may hit a blood vessel when injecting, but this is unlikely if the person follows the six rights of medication safety: Washing hands, using a new needle each time, avoiding touching the injected site and not shaking the syringe before use. If a blood vessel is accidentally hit, the patient should immediately notify their healthcare provider and follow their organization’s procedure for an adverse reaction to medication.