Structure and Function of the Skin : A Comprehensive Guide to the Epidermis, Dermis, and Subcutaneous Tissue

The skin is the largest organ of the body, protecting us against pathogens, environmental factors, regulating our body temperature, and enabling us to feel various sensations. The skin is made up of three main layers and is susceptible to many problems and conditions. This fleshy layer of the body acts as the first line of defense between the external and internal environment. Read on to learn more about the structure and function of the different layers of the skin – the epidermis, dermis, and subcutaneous tissue.

The skin is the largest organ of the body, composed of water, fats, protein, and minerals. The skin carries out several critical functions of the body, including protecting the body against pathogens, and regulating the body’s temperature, while allowing us to feel sensations like hot and cold. The skin is one of the organs that makes up the integumentary system of the body, together with nails, hair, and glands.^(1, 2, 3)

The skin is made up of three main layers. These include:

• Epidermis – this is the topmost and outermost layer of the skin. It is a waterproof layer that protects the body and it lends us our skin tone.
• Dermis – The layer of skin located underneath the epidermis is known as the dermis. It contains blood vessels, tough connective tissues, sweat glands, and hair follicles as well.
• Subcutaneous Tissue (Hypodermis) – This is the deeper subcutaneous tissue which is also known as hypodermis. It is made up of connective and fat tissue.

Let us take a closer look at these three layers of the skin, their structure, and function.

1. Epidermis Layer

   The epidermis is the outermost or topmost layer of the skin. This is a waterproof layer and it lends us our skin tone. The main functions of the epidermis layer are:

   • To produce new skin cells
   • To give color to the skin
   • To protect the body from external threats of pathogens and environmental factors like ultraviolet (UV) light and pollution

   In a single day, human beings end up shedding about 500 million skin cells. It may surprise you to learn that the outermost part of the epidermis layer is made up of 20 to 30 layers of dead cells only.^(4, 5)

   In the lower layers of the epidermis, new cells are constantly being manufactured, and over a time period of approximately four to five weeks, these new cells start making their way to the surface. Once they reach the surface, they become hard and eventually replace the dead and shedding older skin cells.⁽⁶⁾

   Inside the epidermis layer, there is a certain type of cell known as keratinocytes. These are the most common type of cells in the epidermis and their function is to act as a barrier against parasites, fungi, bacteria, viruses, ultraviolet (UV) rays, heat, and even prevent water loss. It is interesting to note that the epidermis does not contain any blood vessels. The epidermis is also where we find a type of skin cell known as melanocytes. Melanocytes produce melanin, which is the pigment that gives our skin its color. Melanocytes also protect your skin from the harmful effects of UV rays.^(7, 8, 9)

   The epidermis layer also contains Langerhans cells that function as the sentinels for the immune system in your skin. Langerhans cells determine the kind of immune response the body should evoke by looking at the environmental context where they encounter any foreign invaders. Langerhans cells are also responsible for ensuring there is a continuous state of immune tolerance within the body which prevents any harmful and unnecessary immune response.^(10, 11)

   The epidermis is further made up of five layers. These include:

   • Stratum corneum
   • Stratum lucidum
   • Stratum granulosum
   • Stratum spinosum
   • Stratum germinativum

   The second layer of the skin, beneath the epidermis, is known as the dermis and both these layers are divided by a thin sheet of fibers called the basement membrane.

2. Dermis Layer

   The dermis is the layer under the epidermis and it functions as the connective tissue that protects the body from strain and stress. The dermis layer lends the skin its elasticity and strength. Some of the other functions of this layer of the skin include:⁽¹²⁾

   • To manufacture oil and sweat in the glands located here.
   • To provide blood to the skin.
   • To enable the skin to feel sensations.
   • To grow body hair.

   The main reason why the dermis layer is able to perform these functions is that it contains the blood vessels, hair follicles, and lymphatic vessels. This layer is also home to many glands, including the sebaceous (oil) and sweat glands. Sebaceous glands produce sebum, which is an oil that provides lubrication and waterproofs the body’s hair.

   The dermis is also home to receptors that help detect pressure, pain, and heat. The pressure receptors in the dermis layer are known as mechanoreceptors, while the pain receptors are known as the nociceptors, and the heat receptors are known as thermoreceptors.⁽¹³⁾ 

   One thing to be aware of is that if the dermis layer stretches too much, for example during pregnancy, it can tear. This is what shows up later on the epidermis in the form of stretch marks.⁽¹⁴⁾

   The dermis is further divided into two layers known as the papillary region and the reticular region. The papillary region is home to the connective tissue, and it has finger-like projections that reach up into the epidermis layer. These projects lend the dermis a sort of bumpy surface and are known to give rise to the patterns of a person’s fingertips. On the other hand, the reticular region is home to dense and irregularly organized connective tissue. There are protein fibers present in this layer that lends the skin its elasticity and strength.⁽¹⁵⁾

3. Subcutaneous or Hypodermis Layer

   The deepest layer of the human skin is known as the hypodermis or subcutaneous tissue layer, also known as the subcutis. It is important to understand that this layer is not technically part of the skin, but it is responsible for keeping the skin attached to bones and muscles. At the same time, the subcutaneous tissue also provides the skin with blood supply and nerves.

   The hypodermis layer is comprised of mostly fat, elastin, which is a type of elastic protein that helps the tissues go back to their normal shape after they stretch, and connective tissue. The high levels of fat in this layer help provide insulation to the body and prevents you from losing too much of body heat. This fat layer also functions as protection since it provides padding to the bones and muscles.

   The exact thickness of the hypodermis layer depends on which part of the body they appear in and varies accordingly. For example, you will see that the area around the eye is relatively thinner than the cheeks to allow for easy movement of the eye.

   Another function of the subcutaneous layer is that it helps the nerves and blood vessels. The nerves and blood vessels in the dermis layer get larger when they are in the hypodermis layer. These blood vessels and nerves branch out further and connect the hypodermis to the rest of the body.⁽¹⁶⁾

The skin has numerous critical functions in the body. Some of them include:^{(17, 18, 19)}

• The skin protects you from the environment. This is one of the most important functions of the skin as it keeps pathogens at bay and prevents them from entering the body through the skin and causing harm.
• It prevents water loss. Since humans have thick skin, it helps prevent water loss. If we go to the desert region, people in that region actually have thicker skin to prevent water loss due to the dry air. Organisms that have thin skin have a high likelihood of losing water and they need to therefore remain near water to prevent their skin from drying out.
• The skin makes us feel all types of sensations. It is the main sense organ of the body and we can sense touch, pressure, hot, cold, pain, and pleasure. There is a network of nerves in the layers of the skin that help transmit these signals to the brain. This is what allows us to respond appropriately to a certain stimulus.
• The skin also carries out the role of regulating the body temperature. The skin loses water through sweating and cools itself. This removes the heat from the body. At the same time, the skin allows the hot blood to come up to the surface of the skin, where the heat gets radiated out of the skin. When we see goosebumps develop on our skin, it is also a response of the skin to temperature regulation.
• The skin, surprisingly, also makes new skin. The epidermis layer continuously manufactures new skin cells, which replace nearly 40,000 old skin cells that the body sheds on a daily basis. Technically, you end up having new skin every 30 days.
• The skin also protects the body. The Langerhans cells present in the epidermis layer are part of the body’s immune system and they help fight off many infections and pathogens.
• The skin also provides you with skin color as the epidermis contains melanocytes which produce a pigment known as melanin. Melanin is a pigment that provides the skin with its color.
• The exact melanin you have is what determines what color of skin, hair, and eyes you have. It is observed that people who manufacture more melanin have darker skin.
• The skin is also responsible for storing fats and water in the tissues. These provide the extra insulation our body needs, especially in cold weather.

Being the largest organ of the body, the skin has many important functions to play. Not only does the skin protect the body against germs, but it also regulates your body temperature, lends color to the skin, manufactures new cells, and even lets us feel all types of sensations. The skin is made up of three layers namely, the epidermis, the dermis, and the hypodermis, or the subcutaneous layer. Taking good care of your skin will ensure that you do not become susceptible to common conditions like acne, eczema, wrinkles, skin cancer, psoriasis, and many others.

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