Subcutaneous Tissue Structure and Functions

The Deepest Layer of Skin

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Subcutaneous tissue, also known as the hypodermis, is the innermost layer of skin. It's made up of fat and connective tissues that house larger blood vessels and nerves.

It acts as an insulator to help regulate body temperature. The thickness of this subcutaneous layer varies throughout the body and also from person to person.

Hands of woman applying hand cream
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Layers of the Skin

The skin is composed of three layers:

Subcutaneous Tissue Structure

Several structures and specialized cells exist within the subcutaneous tissue. These include:

  • Collagen and elastin fibers (these attach the dermis to muscles and bones)
  • Fat cells
  • Blood vessels
  • Sebaceous glands
  • Nerve endings
  • Hair follicle roots

The hypodermis is largely composed of adipose tissue (fat tissue), which is made up of adipocytes, or fat cells. The amount of adipose tissue varies throughout the body. It's thickest in the buttocks, the palms of the hands, and the soles of the feet.

The size of adipocytes is determined by a person's nutrition habits. Generally, a person who maintains a healthy diet and exercise habits has smaller adipocytes and is less likely to be overweight.

The location and thickness of subcutaneous tissue differ by sex. Men tend to accumulate more around the abdomen and the shoulders, while women accumulate it around the thighs, hips, and buttocks.

Subcutaneous Tissue Functions

Subcutaneous tissue has several functions in the body. It helps provide insulation, regulate temperature, and store fat. Because subcutaneous tissue is the deepest layer of the skin, it attaches the other skin layers to tissues under the skin, like bones and muscles.

Energy Reserve

The adipose tissue in the epidermis acts as an energy reserve. Once the body uses up energy acquired from consuming carbohydrates, it turns to adipose tissue as a fuel source, leading to weight loss.

Hormone Production

Adipocytes can swell or shrink depending on whether fat is being stored or used. The hormone leptin is secreted by fat cells to help control appetite and signal when you are full.

Provides Protection

This fat acts as armor that protects muscles, bones, organs, and more delicate tissues. Think of subcutaneous tissue as the protective gear that athletes such as football and ice hockey players wear. It's the body's natural padding that cushions and protects your bones and muscles if you fall or take a hit.

Regulates Body Temperature

Subcutaneous tissue also regulates body temperature by making sure your internal temperature isn't too high or too low. The hypodermis essentially insulates the body, allowing you to go outside on a cold day without getting hypothermia (a dangerous condition that can result in freezing to death).

Subcutaneous Injections

Since the subcutaneous tissue contains a limited network of blood vessels, medications injected here are absorbed gradually over time. This makes them an ideal route for many drugs. That's why many medications are injected into the hypodermis.

Medications that may be given by subcutaneous injection include:

  • Epinephrine for allergic reactions
  • Some vaccinations
  • Insulin
  • Some fertility drugs
  • Some chemotherapy medications
  • Morphine
  • Growth hormone
  • Anti-arthritis drugs

The parts of the body that have greater concentrations of subcutaneous tissue make them ideal injection sites. These include the:

  • Outer part of the upper arm
  • Middle part of the abdomen
  • Front of the thigh
  • Upper back
  • Upper part of the buttocks

Effect of Age on Subcutaneous Tissue

As you age, subcutaneous tissue starts to thin out. This weakened layer of insulation makes the body more sensitive to the cold because having less tissue makes it harder to stay warm.

The loss of subcutaneous tissue due to aging also causes the body to sweat less, making it harder to stay cool in warm weather. It can also affect the body's reaction to certain medications that are absorbed by subcutaneous tissue.

While the hypodermis isn't visible, it can dramatically affect the appearance of the skin and how aging impacts the skin, specifically in the area of the face and neck.

With aging, the volume of facial fat decreases, and there is less supportive tissue to support the skin's normal elasticity. The facial skin begins to droop and sag; the bones and muscles of the face also lose volume. Some people may choose to receive chemical cosmetic fillers to "plump up" the skin in these areas.

Frequently Asked Questions

12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Heather L. Brannon, MD
Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.