Photoaging 201: How the sun affects our skin from the outside in

Published on:  July 19, 2020

Skin Anatomy and Epidermal Changes

Welcome to Part 2 in our series on how UV exposure contributes to skin damage. 

In Part 1, we went over skin anatomy, and then we talked about how cell turnover rate slows throughout our life-times and mentioned that cellular turnover is also reduced in chronically sun exposed (photoaged) skin.  Finally, we went on an in-depth discussion of cellular senescence and talked about a few ingredients that boost our bodies ability to remove senescent skin cells.

If you didn’t catch Part 1, head back and read it here:  Photoaging 101: Skin Cell Turnover and Cellular Senescence

Now, we’re going to jump right into Part 2. 

Today, we’ll talk about how sun exposure changes the skin from the outside in.  We’re going to start out with a brief anatomy review and then focus on changes in the epidermis (outer skin layer) in today’s post.

Brief Anatomy Review

Let’s start out with a picture of the dermis (blue) and epidermis (pink/red) with the stratum corneum overlying the epidermis. 

We’re going to look at what happens to our skin over the course of our lives from the outside in starting with the epidermis and working our way down into the junction (or bridge) between the epidermis and dermis and then keep moving right on down into the dermal layer. 

structure of the skin dermal epidermal junction (DEJ), dermis, and epidermis

What goes on in the epidermis and dermis?

The epidermis contains skin cells capable of producing pigment and responsible for resupplying our stratum corneum (that outermost skin layer) as we shed dead skin cells. 

The dermis contains capillaries, nerves, hair follicle origins, and oil glands.

The dermis provides nutrients to the epidermis, and it does that through the dermal-epidermal junction (DEJ), which is also known as the basement layer.

This basement layer connects the epidermis to the dermis.

Let’s look at how our skin changes over our lifespan and how those changes are accelerated by sun exposure.

Changes in the epidermis


Once we hit 30, we start to lose melanocytes (the pigment producing skin cells) at a rate of between 8% and 20% each decade (Reference 1).  This loss of melanocytes is referred to as melanocyte dropout, and while the rate of decline isn’t quite as fast in sun exposed areas of our body, we often wind up with areas of hypopigmentation and hyperpigmentation on sun exposed skin due to two things:

  • irregular spacing of melanocytes
  • impaired melanocyte function

If you’ve gone back to read part 1, you may be wondering where the melanocytes are within the epidermis.

Melanocytes reside in the stratum basale, the very bottom layer of the epidermis right above the basement membrane that connects the epidermis with the dermis.

Rete Ridges (or rete pegs)

If you look at the image below, you’ll notice some fingerlike projections extending from the dark pink epidermis down into the light pink dermis/basement layer.  In young skin, there are quite a few of these fingerlike projections just like in the picture below.  

These projections are called rete ridges, and both chronic sun exposure and chronological aging cause these ridges to become flatter and flatter.  Researchers compared more photo-exposed areas of our bodies to less photo-exposed areas of our bodies and found that rete ridges were significantly flatter in photo-exposed regions of our skin. 


the structure of rete ridges in our skin

structure of rete ridges in our 30s and 70sstructure of rete ridges in our skin in our early 20s and at 80 years old This figure shows the appearance of rete ridges at various decades of life (Reference 2)

Why does it matter that these rete ridges go flat? 

Well, the flatter the junction between the dermis and epidermis, the less surface area connecting the two layers. 

Since the epidermis receives its nutrition from the dermis, decreasing the surface area connecting the two layers reduces the epidermis’ ability to receive nutrients from the dermis. 

A flat connection between the two layers also makes the epidermis more prone to tearing.

That's a wrap

Today’s post shows two key changes in the epidermis due to chronic sun exposure and chronological aging.  There are still two more ways the sun causes our skin to act older.  One of those ways is by changing the structure of the dermal-epidermal junction, the bridge between the dermal and epidermal layers.  And, then there are changes that happen in the dermis in photo-exposed (and chronologically aged) skin.

I may circle back to those in a future post, but I think what we've covered so far gives you a great idea of just how damaging the sun's rays can be.

As with everything, balance is key.  Sunlight is necessary for life.  We need it for Vitamin D generation, our soul needs it, our mind needs it for sanity, and there's nothing like the feeling of sunlight on your skin.  But, we've got to be careful with it.  Sunlight is a powerful force, and too much of it is damaging.

That's why protective clothing, shade, and antioxidants, frequently applied, are such a good thing - to help us moderate our sun exposure.  If you're looking for a great antioxidant spray, look no further than Marine Layer Antioxidant Spray

And, if you're wondering why antioxidants are so great for body and skin, check out this post.


Reference 1 A Review: Effects of Aging on Skin Structure and Function

Reference 2 Chronological ageing induces the instability of hemidesmosome components

Other Resources

Structural changes associated with aging skin


Brandy Searcy founder Rain Organica

About the Author

Brandy's a formulation scientist and self-proclaimed health geek who loves hiking, gardening, bird-watching, and body boarding. 

Her struggle with acne during her teens and 20s led to a holistic and healthy approach to skincare, embracing skin as an organ to be loved and cared for rather than a canvas to wage war on. 

Since 2008, she's been developing all-in-one products for a simple routine at home, & Rain Organica started when her backpacking friends asked for a portable skincare routine to keep their skin healthy & happy on and off the trails.

You can try Rain Organica for yourself with The Essentials Kit, a complete skincare routine in just 3 steps.

Brandy's LinkedIn Bio

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