Skin Health Subcutaneous Tissue Structure and Functions The Deepest Layer of Skin By Heather L. Brannon, MD Updated on August 24, 2022 Medically reviewed by Katlein Franca, MD Print Table of Contents View All Table of Contents Structure Function Injections Effect of Age Frequently Asked Questions 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. west / Getty Images Layers of the Skin The skin is composed of three layers: Epidermis Dermis Subcutaneous tissue 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 cellsBlood vesselsSebaceous glandsNerve endingsHair 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 reactionsSome vaccinationsInsulinSome fertility drugsSome chemotherapy medicationsMorphineGrowth hormoneAnti-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 armMiddle part of the abdomenFront of the thighUpper backUpper 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. What Materials Are Used for a Liquid Face Lift? Frequently Asked Questions What are four functions of subcutaneous tissue? It's important for storing fat (energy storage), producing hormones (leptin), regulating body temperature (insulation), and protecting the body. Learn More: The Individual Layers of Skin and Their Functions Where is subcutaneous tissue located? It's the innermost layer of skin. It's located underneath the outer layers of the skin (epidermis and dermis). Learn More: The Anatomy of the Skin Are there nerves in subcutaneous tissue? Yes. Subcutaneous tissue contains connective tissues that hold nerves and blood vessels. Learn More: The Integumentary System: Your Skin, Hair, Nails, and Glands 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. Driskell RR, Jahoda CA, Chuong CM, Watt FM, Horsley V. Defining dermal adipose tissue. Exp Dermatol. 2014;23(9):629–631. doi:10.1111/exd.12450 Lopez-Ojeda W, Pandey A, Alhajj M, et al. Anatomy, Skin (Integument) In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441980/ Agarwal S, Krishnamurthy K. Histology, Skin. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537325/ Derraik JG, Rademaker M, Cutfield WS, et al. Effects of age, gender, BMI, and anatomical site on skin thickness in children and adults with diabetes. PLoS One. 2014;9(1):e86637. doi:10.1371/journal.pone.0086637 Alexander CM, Kasza I, Yen CL, et al. Dermal white adipose tissue: a new component of the thermogenic response. J Lipid Res. 2015;56(11):2061–2069. doi:10.1194/jlr.R062893 Ahn AC, Kaptchuk TJ. Spatial anisotropy analyses of subcutaneous tissue layer: potential insights into its biomechanical characteristics. J Anat. 2011;219(4):515–524. doi:10.1111/j.1469-7580.2011.01407.x Kim H, Park H, Lee SJ. Effective method for drug injection into subcutaneous tissue. Sci Rep. 2017;7(1):9613. doi:10.1038/s41598-017-10110-w Mateos MV, San Miguel JF. Safety and efficacy of subcutaneous formulation of bortezomib versus the conventional intravenous formulation in multiple myeloma. Ther Adv Hematol. 2012;3(2):117–124. doi:10.1177/2040620711432020 Caso G, McNurlan MA, Mileva I, Zemlyak A, Mynarcik DC, Gelato MC. Peripheral fat loss and decline in adipogenesis in older humans. Metabolism. 2013;62(3):337–340. doi:10.1016/j.metabol.2012.08.007 Zhang S, Duan E. Fighting against Skin Aging: The Way from Bench to Bedside. Cell Transplant. 2018;27(5):729–738. doi:10.1177/0963689717725755 National Cancer Institue: SEER Training Modules. Layers of the skin. Ishida T, Takeuchi K, Hayashi S, et al. Anatomical structure of the subcutaneous tissue on the anterior surface of human thigh. Okajimas Folia Anat Jpn. 2015;92(1):1-6. doi:10.2535/ofaj.92.1 Additional Reading MedlinePlus. Aging Changes in the Skin. MedlinePlus. Subcutaneous (SQ) Injections. 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. See Our Editorial Process Meet Our Medical Expert Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit