Skin 101: Why It Matters When Formulating

Understanding the skin's structure in relation to our own skincare needs and the ingredients needed to achieve those goals is vital to formulating effective and safe products.

Layers of the epidermis. From the bottom (the younger/newer skin) to the top (the older/mature skin).

Let's do a brief overview of each layer, starting from the bottom:

• Basal layer - the deepest layer of the epidermis, it sits above the dermis and is responsible for generating new cells and protecting the upper layers of the epidermis thru the creation of keratin - this starts the keratinization process

• Spinous layer - the layer where keratinocytes become tightly bound together and gives the epidermis structural integrity. Interestingly, lamellar granules, which are the first sign of keratinization, first appear here. This introduces lipids such as ceramides, cholesterol, and fatty acids (among other things) to the epidermis - fun fact: as these cells migrate towards the top, these lipids are what coat the surface of our skin creating a kind of barrier affect

• Granular layer - the layer that contains the previous discussed granules and is responsible for a waterproof barrier that helps to prevent fluid loss, it is often thought that the health of this layer directly affects water loss thru the cornified layer

• Clear layer - this layer is only present in thicker skin like our palms and soles of our feet

• Cornified (Corneum) layer - most superficial layer of the epidermis, these cells that have migrated from the basal layer have completed the keratinization process and are typically arranged in an offset brick pattern. This outer layer serves as a protective barrier, keeping the bad things out and the good things in. One function, which we have all probably heard of is the evaporation of water from the skin, aka.... transepidermal water loss (TEWL)

  *Please see online references[1] for more information on skin structure*

One thing to note is that the average cell cycle lasts about 25 - 42 days, as we age this timeframe can be as long as 60 days. This is one reason that when trying new skincare products we want to be consistent with it for some time to really determine if something is working for us or not.[2]

The last science-y thing to discuss is the Dermis. It lies under Basal layer and is responsible for producing collagen and elastin. Here are some fun facts about the Dermis and it's components....

• Collagen Type I compromises 80% to 85% of the dermal matrix

• Collagen gives strength and structure to the skin

• Collagen synthetization requires vitamin C, iron (Fe++), and alpha-ketoglutarate (AKG - I deep dove into this for several hours and found it very interesting - but it is far beyond the scope of this blog)

• Elastin gives the skin it's stretchiness and elasticity

• Elastin are made of protein

  *Please see online references[3] for more information on skin structure*

So...that is a VERY condensed overview. I highly recommend anyone who wants to make skincare products for themselves to do more in depth research - it really is a fun (and educational) read, if you like this sort of stuff. But the question remains....why does this even matter?

Well it matters because when formulating products we want maximum efficacy - or as I like to say "more bang for the buck". We want results. Some ingredients when formulated a certain why do allow some dermis penetration. Since the skin is very water resistant, certain lipids are capable of getting further into the skin layers. This was a great scientific article that discusses the penetration of natural oils into the skin and their penetration enhancement potential. Skip to section 2 and 5 to get a general overview...but to summarize, they were using different oils to measure the delivery of an ingredient, DHQ, and found that certain oils such as soybean and olive oil did increase its penetration. There is a belief that oleic acid acts as a penetration enhancer, helping to deliver other ingredients deeper into the skin, however due to this it also does not hydrate as well as other fatty acids (here is looking at you. So depending on what your goal is for a product will dictate what and how much of an ingredient is used in your formulas.

In my research for this post I came across a Pub Med abstract that discussed fatty acid penetration for Linoleic, oleic, palmitoleic, palmitic, and stearic fatty acids. Linoleic acid penetrated the skin and changed the distribution of all the fatty acids that were used. Palmitoleic or oleic acid increased the amounts of singular fatty acids. Saturated fatty acids had very low penetration, but increased the amounts of linoleic acid in both skin layers (A-MAZING!!). These results indicate that topical application of fatty acids on the skin surface make redistribution of fatty acids in the cornified layer and also in the lipid content of the full epidermis and dermis layers.{4} This is one reason I am a huge proponent for people to incorporate topical oils into their skincare routine. Even those with acne. There is an oil for everyone - it is necessary for all human skin, as we have just learned.

[1] Baumann, Leslie. Cosmetic Dermatology (2009). https://rlmc.edu.pk/themes/images/gallery/library/books/Dermatology/Baumann%20L.%20%20Cosmetic%20Dermatology%20and%20Medicine%20%202009.pdf (Chapter 1: Basic Science of the Epidermis)

[2] Harmon Pippa. The Skin Cycle Explained. Renude Blog. https://renude.co/blog/skin/the-skin-cycle-explained-97

[3] Baumann, Leslie. Cosmetic Dermatology (2009). https://rlmc.edu.pk/themes/images/gallery/library/books/Dermatology/Baumann%20L.%20%20Cosmetic%20Dermatology%20and%20Medicine%20%202009.pdf (Chapter 1: Basic Science of the Dermis)

[4] Multiple contributors. Fatty acids penetration into human skin ex vivo: A TOF-SIMS analysis approach. https://pubmed.ncbi.nlm.nih.gov/28253633/