What Is the Hypodermis?

The Subcutaneous Layer of Skin

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The hypodermis is the bottom layer of skin. Also known as subcutaneous tissue, the hypodermis insulates and protects the body, stores energy (fat), helps to regulate body temperature, and connects the skin to muscles and bones.

The hypodermis is one of the three layers of human skin, the others being the epidermis (outer layer) and dermis (middle layer). Together, these layers provide a barrier against fluids, infection, and trauma.

This article discusses the hypodermis layer of the skin. It explains the anatomy and function of the subcutaneous tissue. It also covers potential health conditions and the effect of aging on the hypodermis.

normal skin pathology
Normal skin pathology.

DermNet / CC BY-NC-ND

Anatomy of the Hypodermis

The hypodermis is the innermost or subcutaneous layer of the skin. Most of the body's fat is stored in this layer. It provides insulation, protection, temperature regulation, and connection between the bones and muscles.

Structure

The hypodermis contains collagen, fibers, adipose tissue (fat cells), connective tissue, larger nerves and blood vessels. It also includes macrophages, cells that are part of the immune system and help keep your body free of intruders.

Location

The hypodermis is the innermost layer of the skin located under the dermis (outer layer) and the epidermis (middle layer). The thickness of the hypodermis varies in different regions of the body and can vary considerably between different people.

The hypodermis layer also provides shaping and contouring. For those assigned male at birth, the hypodermis is thickest in the abdomen and shoulders. Whereas the hypodermis for those assigned female at birth is generally thickest in the hips, thighs, and buttocks.

Function

The functions of the hypodermis include:

  • Fat and energy storage: Fat cells (adipocytes) make up the fatty (adipose) tissue that stores energy for the body. The hypodermis also helps to create hormones such as estrogen and leptin.
  • Protecting the body: The fat in the hypodermis acts like padding or a shock absorber that protects the bones, muscles, and organs from cold, trauma, or impact.
  • Regulating body temperature: This layer functions as an insulator by trapping or conserving heat, which offers protection against the cold. It also protects the body against heat through sweating.
  • Attaching the skin to muscle and bone: The hypodermis contains connective tissue which connects the skin to bones, muscles, and organs.

Connective tissue also supports structures such as nerves and blood vessels.

Associated Conditions

The following are medical disorders and procedures related to this unique layer of the skin.

Hypothermia and Overheating

The hypodermis is essential for body temperature regulation. It traps heat, protects you from the cold, and causes sweating, protecting you from the heat.

With age, the hypodermis thins. This is one of the reasons that older people are more prone to hypothermia. Thinning of the hypodermis may also mean that you sweat less. Lack of sweating can lead to health conditions such as heat exhaustion and heatstroke.

Injections

Medications can be injected into different areas of the body, such as the vein (intravenous or IV), muscle, under the dermis (intradermal), or in the hypodermis (subcutaneous layer).

Medications given by subcutaneous injection (subQ) are absorbed more slowly than drugs given by intravenous injection. This makes subQ injections an ideal route for many drugs, especially those that are self-administered.

Examples of medications that may be given by subQ injection include:

Some medications can only be given through one route, while others can be given through multiple routes. It depends on the type and goal of the medication and how it's best absorbed in the body.

Obesity

Body fat in the hypodermis layer is called subcutaneous adipose tissue (SAT). This is different than visceral adipose tissue (VAT) that lines internal organs. Excess fat in either area leads to obesity.

Both types of fat have received a lot of attention in recent years due to the growing rate of obesity. Studies note that not all body fat is equal, at least with respect to its role in metabolic syndrome and heart disease.

The Hypodermis and Aging

While the hypodermis is not visible, it can dramatically affect the appearance of the skin. This is due to the way 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 normal turgor or elasticity of the skin.

As a result, the facial skin begins to droop and sag, resulting in a look that can be interpreted as appearing tired. The bones and muscles of the face also lose volume.

Summary

The hypodermis is the innermost layer of the skin. It stores fat and energy, pads and protects the body, attaches skin to the bones and muscle, and is very important in maintaining body temperature.

This layer of the skin thins with age, increasing the risk for hypothermia or heat exhaustion. It provides shaping and contour. The thickness varies per person, with excess fat in this layer leading to obesity. The hypodermis layer can be used for injections with some types of medication.

Frequently Asked Questions

  • What is the function of the hypodermis?

    The hypodermis fulfills several important functions:

    • Stores fat (energy)
    • Offers protection by acting as a shock absorber
    • Attaches upper skin layers (dermis and epidermis) to bones and cartilage
    • Supports structures inside it, including nerves and blood vessels
    • Regulates body temperature
    • Produces hormones
  • What are the contents of the hypodermis?

    The hypodermis contains fibroblasts (a type of cell commonly found in connective tissues),adipose tissues (fat cells), macrophages (a type of white blood cell that protects the body from harmful bacteria), and connective tissues that hold blood vessels and nerves.

  • What is the difference between dermis and hypodermis?

    There are three layers of the skin, including the epidermis, dermis, and hypodermis. The dermis is below the epidermal layer of skin that you see and above the hypodermis. Between them, it works to produce sweat and oil, grow hair, and provide sensitivity and structure to the skin.

10 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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  6. National Library of Medicine (NIH). Subcutaneous (SQ) injections.

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  10. National Human Genome Research Institute. Fibroblast.

Additional Reading

By Brandi Jones, MSN-ED RN-BC
Brandi is a nurse and the owner of Brandi Jones LLC. She specializes in health and wellness writing including blogs, articles, and education.

Originally written by Natalie Kita