The Hypodermis Layer of the Skin Structure and Function

The Anatomy and Physiology of the Subcutaneous Layer of the Skin

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What is the hypodermis or subcutaneous layer of the skin? What type of tissue is this (anatomy and structure) and what is its purpose (physiology or function)? How is this layer important in aging, and what medical conditions affect the hypodermis? What plastic surgery procedures are done on this layer to reduce the signs of aging?

normal skin pathology
Normal skin pathology.

DermNet / CC BY-NC-ND


The hypodermis is the innermost (or deepest) and thickest layer of skin. It is also known as the subcutaneous layer or subcutaneous tissue.

The layers of the skin include the epidermis (the outermost layer), the dermis (the next layer which is loaded with blood vessels and nerves), and then the hypodermis.

Anatomy and Structure

The hypodermis contains the cells known as fibroblasts, adipose tissue (fat cells), connective tissue, larger nerves and blood vessels, and macrophages, cells which are part of the immune system and help keep your body free of intruders.

The thickness of the hypodermis varies in different regions of the body and can vary considerably between different people. In fact, the thickness of the hypodermis plays an important role in distinguishing between males and females. In men, the hypodermis is thickest in the abdomen and shoulders, whereas in women it is thickest in the hips, thighs, and buttocks.

Function (Physiology)

The hypodermis may at first be viewed as tissue which is used primarily for the storage of fat, but it has other important functions as well. These functions include:

  • Storing fat (energy storage)
  • Protection (think buttocks and sitting on a hard chair)
  • Attaching the upper skin layers (dermis and epidermis) to underlying tissues such as your bones and cartilage, and supporting the structures within this layer such as nerves and blood vessels
  • Body temperature regulation: This layer functions as an insulator, offering protection against the cold, and protects the body against heat as well through sweating.
  • Hormone production: The hormone leptin is secreted by fat cells to tell the body it is time to stop eating.

Conditions Which Affect the Hypodermis

There are several medical disorders and medical procedures which are related to this unique layer of the skin:

Hypothermia and Overheating: The thinning of the hypodermis with age is one of the reasons that older people are more prone to hypothermia. If you are ordinarily hot, this news is not necessarily so good. The thinning of the hypodermis also may mean that you sweat less, and a lack of sweating is important in conditions such as heat exhaustion and heatstroke.

Injections: While many medications are given intravenously, some are injected into the hypodermis (subcutaneous layer). Examples of medications which may be given by subcutaneous (subQ) injection include epinephrine for allergic reactions, some vaccinations, insulin, some fertility drugs, some chemotherapy medications, growth hormone, and anti-arthritis drugs such as Enbrel. Medications given by subcutaneous injections are absorbed more slowly than drugs given by intravenous injection, making subQ injections an ideal route for many drugs.

Obesity: Excess body fat is located in the hypodermis, a layer that has received a lot of attention in recent years due to the growing rate of obesity, and the thought that not all body fat is equal, at least with respect to the role it may play in metabolic syndrome and heart disease.

The Hypodermis and Aging

While the hypodermis is not visible, it can have a dramatic effect on the appearance of the skin and 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 and elasticity of the skin. 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.

Hyaluronic Acid Fillers for Aging

To correct the loss of facial volume and counteract the effects of aging, hyaluronic acid fillers, used specifically for volume replacement, can be injected. Hyaluronic acid is compatible with the body and may be a good choice for facial filler. It is found naturally in the body with high concentrations in soft connective tissue and the fluid that surrounds the eyes. It is also found in cartilage and joint fluids.

An injection of hyaluronic acid filler will support facial structures and tissues that have lost volume and elasticity. It acts as a volumizer by bringing water to the surface of the skin, making it look more supple and fresh. It plumps and lifts cheeks, jawlines, and temples. The filler can also fill out thin lips and plump hands that have begun to sag.

While side effects are rare, there are risks to injections of hyaluronic acid. There is a risk of allergic reactions, and of course, the cosmetic result may not be what you had hoped.

Bottom Line on the Hypodermis

While many people think of the hypodermis as simply a layer of the skin which stores fat, it is also very important in maintaining body temperature and other functions.

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.

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8 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
  • Kumar, Vinay, Abul K. Abbas, Jon C. Aster, and James A. Perkins. Robbins and Cotran Pathologic Basis of Disease. Philadelphia, PA: Elsevier/Saunders, 2015. Print.