MARCH 31, 2022

Written by Kristen McNary

Let’s get into the nitty gritty. I believe that knowing the basic anatomy and physiology of skin helps you to understand it’s key functions, what it needs to be healthy, function optimally, and how treatments tie in. Knowledge is power, baby. 

The integumentary system includes the layers of the skin; epidermis, dermis, and hypodermis as well as all of the appendages of the skin such as hair, nails, and glands. Our epidermis acts as a physical and biological barrier, protecting us from our external environment. So cool, right? Let’s break it down. 

Layers of the Epidermis: 

Stratum Corneum (Horny layer) – This is the uppermost layer of your epidermis where a cell reaches the final stage of it’s life cycle. Cells in this stage assist in your skin’s protective barrier function as they are mostly flat, hardened or “dried” cells called corneocytes. They naturally shed in a process called desquamation every 4 weeks as a part of the cellular renewal process, although this process slows down as we biologically age and our cell’s function decreases.

Stratum Lucidum – This layer is found only in areas of the body with the most friction or with thicker skin such as the palms of the hand and fingertips as well as the soles of the feet and toes. Cells in this layer are comprised mostly of impermeable keratin to prevent water loss. 

Stratum Granulosum (Granular Layer) – The cells in this phase begin to shed their “shells” and nucleus, and become granular in appearance as they lose water content in order to prepare for the next stage. Hence the term “dead skin cells”.

Stratum Spinosum (Spiny Layer) – The 2nd phase of a keratinocyte’s life cycle, this is referred to as the spiny layer because of desmosomes which bind cells together and transfer nutrients between them. Pigment granules from your melanocytes can be seen here. 

Stratum Basale (Basal Layer) – This is the layer closest to the dermis. Your brand new baby cells with a nucleus are formed here and work their way up to the top through their life cycle. On average every 1 in 10 cells in this layer is a pigment producing cell known as a melanocyte. 

Your skin cells (aka keratinocytes) begin their life cycle at the basal layer where they are ‘born’, then work their way up to the stratum corneum where they will eventually desquamate (shed). The health and appearance of our epidermis is determined by environmental and intrinsic factors, as well as the function of the components that comprise the layers below. As estheticians, some of our goals while working on the epidermis are to increase your skin’s cellular turnover rate, improve barrier function, and optimize the health of the epidermis and skin overall. These are the key factors to healthy skin, which is the epitome of beauty.   

Layers of the Dermis: 

Papillary Layer – This is the uppermost layer of your dermis which contains nerve endings, lymphatic vessels, capillaries, mucopolysaccharide molecules such as hyaluronic acid and heparan sulfate, and some collagen and elastin fibers. 

Reticular Layer – The collagen and elastin matrix of your skin lies in this layer, making up 4/5 of the dermal layer as a whole. The cells that manufacture collagen, elastin, and histamines are found here as well. 

Hypodermis – The hypodermis is your subcutaneous or adipose tissue which is directly below the dermis. It’s made up of mostly fatty tissue to insulate your body, provide padding for muscle, organs, and bone, and connect your skin to the underlying fascia, bones and muscle. 

The dermis serves as the structural support of your skin. This is where our beloved dermal proteins (collagen, reticulin, and elastin) live as well as nerve endings and blood vessels which deliver nutrients to your tissue. 

Appendages of the skin are extensions of the skin such as hair, nails, and certain glands;

Sudoriforous gland – Sweat gland or any gland that excretes onto the skin. 

Sebaceous gland – A type of sudoriforous gland, sebaceous glands excrete sebum (also known as the oil your skin produces) through the hair follicle. 

Hair Follicle – The pocket which hair grows through. We see these as the pores in our skin.  

I hope you enjoyed this little peek into the anatomy and physiology of your skin. As you can see, skin is a complex and amazing organ and we’ve only just scratched the surface here. The skin is your body’s largest organ and it serves as a protective barrier from your environment. So doesn’t it make sense to protect it right back?



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