What are the 3 layers of your skin? Epidermis, Dermis and Hypodermis

Posted by Dr. Natasha Ryz on

There are 3 layers of tissue that make up your skin:

  1. The Epidermis, the top outer layer.
  2. The Dermis, the middle layer.
  3. The Hypodermis, the bottom or fatty layer.
Layers of Skin

What does the epidermis (top layer of skin) do?

The epidermis is the top layer of your skin that you can see and touch.

The epidermis:

  • Acts as a protective barrier: The epidermis forms a physical barrier, and protects you from the external environment.                                    
  • Makes new skin: The epidermis continually makes new skin cells, called keratinocytes. These new cells are shed and replaced every 30 days.
  • Prevents water loss: The epithelial barrier prevents dehydration and moisture loss from your body.
  • Provides skin color: The epidermis contains melanocytes, cells that produce melanin, the pigment that gives skin its color. Melanin also protect cells of the skin from ultraviolet (UV) radiation damage from sunlight.
  • Protects your body: The epidermis contains Langerhans cells that are part of the body’s immune system. They help fight off invading microbes.
What is the epidermis (top layer of skin) made of?

The epidermis is made of 4 types of cells.

1. Keratinocytes are the major cell type in the epidermis, and make up 95% of the cell population. As keratinocytes mature, they differentiate into corneocytes, which serve as a physical barrier, and protect your body from the external environment.

2. Merkel cells function as mechanoreceptors for the sensation of touch and pressure.

3. Melanocytes make melanin, which defines skin color.

4. Langerhans cells are a part of the skin immune system.

In addition, sensory nerve endings that recognize touch, pressure, temperature as well as pain and itch, may also reach the lower layers of the epidermis. 

Layers of the Epidermis

The epidermis is made of four or five layers of epithelial cells, depending on its location in the body. 

Skin that has four layers of cells is referred to as 'thin skin'. Most of your skin can be classified as thin skin. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. 

'Thick skin' is found only on the palms of the hands and the soles of the feet and is hairless. Thick skin has a fifth layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum.

What is The Stratum Corneum?

The stratum corneum is the most outer layer of the epidermis and is the layer directly exposed to the external environment.

There are approximately 15 to 30 layers of cells called corneocytes in the stratum corneum.

Corneocytes are terminally differentiated from skin cells called keratinocytes, and they compose most if not all of the stratum corneum. They are regularly replaced through desquamation and renewal from lower epidermal layers, making them an essential part of the skin barrier property.

Desquamation is the natural process of shedding skin cells.

New skin cells are formed at the base layer of the skin, and they differentiate and migrate towards the skin surface, in a process that takes approximately 30 days. Nearly a billion cells are lost each day from the surface of adult skin (Milstone et al, 2004). 

What is the Stratum Corneum made of?

The structure of the stratum corneum is described in terms of a ‘brick and mortar’ model in which the protein-rich corneocytes exist within a lipid‐rich matrix containing ceramides, cholesterol, and fatty acids in a ratio of 3:2:1 (Feingold et al, 2007).

The stratum corneum lipids consist of an equimolar mixture of ceramides (45–50% by weight), cholesterol (20–25%), and free fatty acids (10-15%), with lower quantities of cholesterol sulfate and nonpolar lipids (Verdier-Sévrain et al, 2007).

What is the Stratum Lucidum?

The stratum lucidum is a thin layer of cells that are only found in the thick skin on the palms of your hands and fingers, and the soles of your feet.

What is the Stratum Granulosum? 

The stratum granulosum "granular layer" is a thin layer of cells in the epidermis. 

Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in the layer. 

The protein keratin, which is what gives your skin strength, is packaged in little keratohyalin granules. Epidermal skin cells are named “keratinocytes” because they produce keratin.

The keratinocytes in this layer also produce lipids and natural moisturizing factors (NMFs) that strengthen your skin barrier, and help it to hold onto moisture.

The lipids, proteins, and natural moisturizing factors are produced in this layer inside “keratohyaline granules.” These granules are produced by the keratinocytes in the granular layer. It’s called the granular layer because of the presence of these granules.

In the upper layers of the epidermis, the granules break open to release their contents into the space between the cells. This coats the corneocytes with  lipids that help make up the skin barrier.

What is the Stratum Spinosum?

This layer gives the epidermis its strength. The stratum spinosum contains spiny protrusions that hold the cells tightly together to prevent your skin from tearing and blistering.

What is The Stratum Basale?

The stratum basale is a single layer of cells primarily made of basal cells. All of the keratinocytes are produced from this single layer of cells, which are constantly going through mitosis to produce new cells. As new cells are formed, the existing cells are pushed superficially away from the stratum basale.

The melanocyte, a cell that produces the pigment melanin, is also found in the stratum basale. Melanin gives skin its colour, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiation damage.

What does the dermis (middle layer of skin) do?

The dermis makes up 90% of skin’s thickness.

The dermis:

  • Touch: There are nerves in the dermis that help you determine  if something is hot or cold, itchy or super soft. These nerve receptors also help you feel pain.
  • Has collagen and elastin: Collagen is a protein that makes skin cells strong and resilient. Another protein found in the dermis, elastin, keeps skin flexible. It also helps stretched skin regain its shape.
  • Makes sebum: Oil glands in the dermis make sebum, which help keep the skin lubricated, soft and smooth. 
  • Produces sweat: Sweat glands in the dermis release sweat through skin pores. 
  • Grows hair: The roots of hair follicles attach to the dermis.
  • Supplies blood: Blood vessels in the dermis provide nutrients to the epidermis, keeping the skin layers healthy.
What is the dermis made of?

The dermis is composed of a thick layer of dense connective tissue.

The dermis also contains hair follicles, sweat glands, and oil-producing glands called sebaceous glands, that produce sebum.

Sebum is an oily, waxy substance produced by your body’s sebaceous glands and eventually released to the surface of the skin. Sebum is primarily made up of non polar lipids as triglycerides, wax esters and squalene. Sebum coats the skin, seals in moisture, and protects your skin from getting too dry (Pappas, 2009). 

    What does the hypodermis (bottom layer of skin) do?

    The bottom layer of skin, or hypodermis, is the fatty layer.

    The hypodermis:

    • Cushions muscles and bones: Fat in the hypodermis protects muscles and bones from injuries when you fall or are in an accident.
    • Has connective tissue: This tissue connects layers of skin to muscles and bones.
    • Has nerves and blood vessels: Nerves and blood vessels in the dermis get larger in the hypodermis. These nerves and blood vessels branch out to connect the hypodermis to the rest of the body.
    • Regulates body temperature: Fat in the hypodermis keeps you from getting too cold or hot.
    Summary

    There are 3 layers of tissue that make up your skin, the epidermis, the dermis and the hypodermis. 

    The epidermis is the top layer of your skin that you can see and touch. The epidermis forms a physical barrier, and protects you from the external environment. The epidermis continually makes new skin cells, called keratinocytes. These new cells are shed and replaced every 30 days. The epidermis also contains Merkel cells, Langerhans cells and melanocytes, cells that produce melanin, the pigment that gives skin its color.

    The dermis is the middle layer of skin, and makes up 90% of skin’s thickness. The dermis is made of connective tissue, proteins including collagen and elastin, and nerves that help you sense touch and feel pain. The dermis also contains hair follicles, sweat glands, and oil-producing glands called sebaceous glands, that produce sebum.

    The hypodermis is the bottom layer of skin, and is known as the fatty layer. The hypodermis contains fat, connective tissue, nerves and blood vessels. It is rich in fat that cushions you and protects you, and helps to regulate your body temperature.

    The layers of your skin form a barrier and protect you against the external environment.

    Learn more: What is Your Skin Barrier?

    References:

    Arda O, Göksügür N, Tüzün Y. Basic histological structure and functions of facial skin. Clin Dermatol. 2014 Jan-Feb;32(1):3-13. 

    Feingold, K.R. Thematic review series: skin lipids: the role of epidermal lipids in cutaneous permeability barrier homeostasis. J. LipidRes.48, 2531–2546 (2007).

    Kanitakis J. Anatomy, histology and immunohistochemistry of normal human skin. Eur J Dermatol. 2002 Jul-Aug;12(4):390-9; quiz 400-1.

    Milstone LM. Epidermal desquamation. J Dermatol Sci. 2004 Dec;36(3):131-40.

    Pappas A. Epidermal surface lipids. Dermatoendocrinol. 2009 Mar;1(2):72-6.

    Verdier-Sévrain et al. (2007). Skin hydration: a review on its molecular mechanisms. Journal of Cosmetic Dermatology, 6, 75–82.

    Skin Barrier Skin Science

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