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.
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:
Insulin Blood thinners Some vaccinations Some fertility drugs Some chemotherapy medications Human growth hormone (HGH) Some anti-arthritis drugs such as Enbrel (etanercept)
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.
Stores fat (energy)Offers protection by acting as a shock absorberAttaches upper skin layers (dermis and epidermis) to bones and cartilageSupports structures inside it, including nerves and blood vesselsRegulates body temperatureProduces hormones
