Beauty Health

Skin Basics: Skin Layers & Hydration Maintenance

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This is the first section of a five-part series dedicated to moisturizers.

I, by no means, am claiming to be an expert in dermatology. I’ve done my best to be as thorough as possible during my research. If you’re an expert and find an inaccuracy, please let me know and I’d be happy to investigate. This is a learning experience for me too.

TL:DR; Skin can either be dry, dehydrated, or both. Dry skin lacks oil, whereas dehydrated skin lacks water.

Dry skin typically has less visible pores, while dehydrated skin has more visible, darkened pores due to oil. Both can be flaky/dull.

The first step in picking a moisturizer/hydrator is understanding what your skin suffers from.

I truly believe the first step to healthy skin is understanding your skin. In this first segment to a five part segment on moisturizers, I discuss some of the basics of skin to help you better understand your skin, and in later segments how you can select products that complement your skin. Keep reading to learn about skin!

I truly believe that the first step in my quest to healthy skin is understanding my skin. To achieve this, I did a bunch of research to try and learn as much about skin as I could. I’ve compiled everything I’ve learned here, and hopefully it will be insightful and helpful for you too!

Before we discuss moisturizers specifically, I think it makes sense to start with some skin basics. The skin is composed of many layers that work together to maintain skin hydration. By building a good foundational understanding of how the skin maintains hydration, we can better understand the causes of dry/dehydrated skin and, in later sections, understand how moisturizers/hydrators function to help dry/dehydrated skin.

A Quick Note

Okay so, basically I realized that, to further complicate skincare, there’s a big difference between dry skin and dehydrated skin. Which means there’s also a big difference between a hydrator and a moisturizer. – dead –

Dry vs. Dehydrated Skin

Dry skin is a skin ‘type’ (like oily or combination), and results from lack of oil production. Lack of oil production means the skin barrier is less efficient at keeping water in your skin. So, instead the water just evaporates – leading to dry, flaky, irritated skin.

In contrast to dry skin, which is a skin type, dehydrated skin is a skin ‘condition’, and results from lack of water in skin. This leads to flaky, dull skin, and it also means that any skin type can experience dehydration.

Moisturizer vs. Hydrator

To be honest, “moisturizer” is a confusing term. When I think of the word moisture, I think of water. However, in skin care speak, a moisturizer contains chemicals that allow the skin to be able to acquire and retain water (more on this when we talk about moisturizer ingredients in later sections). So, moisturizers themselves don’t really provide water to the skin (more on this when we talk about moisturizer formulations in later sections). In contrast, hydrators directly provide water to the skin, but they don’t help the skin trap or retain that water.

Help! Do I Have Dry or Dehydrated Skin, or Both?

Identifying dry vs. dehydrated skin can be tricky. They seem pretty similar in appearance to be honest. I think the big difference is that dehydrated skin will still have oil production (perhaps enlarged, darkened pores), even if it’s flaky, whereas you won’t see oil production with dry skin. If you’re both dry and dehydrated, you won’t have any oil production and so you need a moisture barrier, and your skin needs water.

Figuring out whether you have dry or dehydrated skin (or both) is definitely a good starting point to help figure out what moisturizer/hydrator you need.

In my opinion, I think both dry and dehydrated skin would benefit from hydrators and moisturizers. Moisturizers trap water in the skin, while hydrators provide water to the skin. It then makes sense to use your hydrator to get some water, then trap it with a moisturizer. Right? Maybe? No? Anyways, let’s continue on to skin layers to figure out how skin maintains hydration.

Skin Layers

The skin is composed of various layers that ultimately interact with each other to help maintain skin hydration. Skin layers, from the most surface layer to the deepest layer, include the epidermis, dermis, and hypodermis. (I don’t think the hypodermis is super relevant for hydration maintenance, so I’m omitting it).


The epidermis is the main layer concerned with hydration maintenance, and it even has its own set of layers.

The most surface layer of the epidermis is called the stratum corneum (SC), and it is arguably the most important layer in terms of hydration maintenance. The SC contains chemicals that absorb water from the environment (these chemicals are collectively known as natural moisturizing factor). The SC is also arranged structurally in a way that minimizes transepidermal water loss (TEWL).

Transepidermal water loss (TEWL) refers to the amount water that is lost from the epidermis to the environment via evaporation. (Trans, in Latin, meaning “through/across” and epidermal meaning of the epidermis – i.e. through the epidermis).

The SC contains chemicals called lipids (fats and oils). SC lipids generally dislike (repel) water, and are tightly packed together. This ultimately makes it difficult for water molecules to travel through the SC to the surface, thus minimizing TEWL. This is important because high TEWL leads to dry, flaky skin since sufficient water is required for proper functioning of skin chemicals.

The next layer of the epidermis is called the stratum granulosum (SG). This layer also contains lipid secretions that prevent water loss.

The next layer of the epidermis is the stratum sinosum. This layer releases a chemical that repels water, again helping to keep water deep in the skin and minimize TEWL.

Lastly, the deepest layer of the epidermis is the stratum basale. This layer doesn’t participate much in moisture maintenance, but for our purpose it helps attach the epidermis to the dermis.

Acid Mantle

Oh! Another thing of super-duper importance. The epidermis is covered with a thin film of water and lipids. This film, called the acid mantle, contains tons of helpful chemicals that keep skin supple and act as further barrier against germs. Because of the acid mantle, the skin has a pH of around 5 (ranges from 4 to 6 depending on the person).

Quick chemistry lesson! pH stands for “potential hydrogen”. Simply, it’s a logarithmic scale from 0 to 14 that tells you how acidic (sour) or basic (bitter) a substance is. Completely pure water has a pH of 7.0, meaning it’s neutral (not acidic or basic). Anything higher than 7.0 is classified as basic, while anything lower than 7.0 is classified as acidic.

So, since our skin has a pH of around 5.0 because of its acid mantle, the skin is slightly acidic.


The dermis is the next deepest skin layer after the epidermis. Most of the skin’s water is stored in this layer. Generally, since the SC layer requires water for proper functioning, the dermis can supply some water to the epidermal layers.

Hydration Maintenance

We know that the SC has various mechanisms of maintaining water. It has chemicals that can pull water from humid environments, a lipid barrier to help prevent water loss, and the deeper dermis that can supply water to the epidermis. Thus, it seems like our skin has lots of mechanisms to minimize TEWL. However, disruption of these mechanisms can lead to increased TEWL, and ultimately dry/dehydrated skin.

Dry/Dehydrated Skin

For skin to look supple and hydrated, the SC must contain more than 10% water. Factors that contribute to increased TEWL include:

  • Climate: Dry weather increases TEWL as low humidity encourages evaporation of water from skin into the air.
    • Suggestion: In dry weather, make sure to moisturize twice daily to prevent TEWL.
  • Hot showers: Long, hot showers soften the oils found in the skin that act as a barrier to TEWL. Softening these oils makes them less effective in keeping water in the skin, and so it’s much easier to lose water from the skin if you have long, hot showers!
    • Suggestion: Try to either have shorter, hot showers, or lukewarm showers. Make sure to moisturize after showering while your skin is still damp (not sopping). It’s beneficial to moisturize after a shower while damp because at this point, there is still plenty of water in your skin. Then, by using a moisturizer, you prevent evaporation of water and trap all that good hydration in your skin.
  • Harsh soaps and detergents: Basic soaps (soaps with pH greater than 7.0), can damage your acid mantle. When we apply highly basic soaps (or event water, but to a lesser extend), we change the pH of our skin. Although this change is temporary, it does last for at least a few hours. This is of note because a lot of the chemicals in our skin function optimally at around pH 5.0. So, changing the pH of our skin, even temporarily, leads to less effective chemical functioning, which leads to less effective skin functioning and ultimately increased TEWL.
    • Suggestion: Use acidic cleansers with pHs closer to our skin. Lots of studies have shown that acidic cleaners are highly beneficial for skin when compared to basic pH cleansers. If cleaning dishes with basic soap, wear gloves to protect your hands.

In Summary

In addition to controlling environmental factors that contribute to dry/dehydrated skin, moisturizers/hydrators are an excellent option. Hopefully you’ve figured out whether you have dry, dehydrated skin, or both. Personally, I think I have dehydrated skin. If I don’t moisturize my skin, I get skin flakes, yet my skin still produces oil.

I know that was a TON of information, plus I’m betting I barely even scratched the surface. But now that we, hopefully, have a basic understanding of skin and how it maintains hydration, let’s talk more specifically about moisturizers and their formulations. (Coming soon!)

~ Hope

Elias, P. (2015). Stratum corneum acidification: how and why?. Experimental Dermatology, 24(3), 179-180. doi: 10.1111/exd.12596

Gfatter, R., Hackl, P., & Braun, F. (1997). Effects of Soap and Detergents on Skin Surface pH, Stratum corneum Hydration and Fat Content in Infants. Dermatology, 195(3), 258-262. doi: 10.1159/000245955

Popkin, B., D’Anci, K., & Rosenberg, I. (2010). Water, hydration, and health. Nutrition Reviews, 68(8), 439-458. doi: 10.1111/j.1753-4887.2010.00304.x

Prakash, C., Bhargava, P., Tiwari, S., Majumdar, B., & Bhargava, R. (2017). Skin Surface pH in Acne Vulgaris: Insights from an Observational Study and Review of the Literature. J Clin Aesthet Dermatol, 10(7), 33-39.

Rawlings, A., & Matts, P. (2005). Stratum Corneum Moisturization at the Molecular Level: An Update in Relation to the Dry Skin Cycle. Journal Of Investigative Dermatology, 124(6), 1099-1110. doi: 10.1111/j.1523-1747.2005.23726.x

Schmid-Wendtner, M., & Korting, H. (2006). The pH of the Skin Surface and Its Impact on the Barrier Function. Skin Pharmacology And Physiology, 19(6), 296-302. doi: 10.1159/000094670

Wickett, R., & Visscher, M. (2006). Structure and function of the epidermal barrier. American Journal Of Infection Control, 34(10), S98-S110. doi: 10.1016/j.ajic.2006.05.295

(2) Comments

  1. So many excellent points I hadn’t thought of! I definitely have dehydrated skin in the winter, but I don’t have dry skin. You made the differentiation so clear. Great post!

    1. Thanks so much! I hope my post was helpful for you. ^-^

      I understand the struggles of dehydrated skin, though mine seems to be all year. I’ve just started my hunt for good skin care products for my skin, so here’s hoping!

      I didn’t know there was a difference between dry and dehydrated skin until I was doing research for this post. I definitely think it’s helpful to be aware of when selecting skin care products (i.e. does my skin lack oil and thus need moisture trapping ingredients, or does my skin lack water and thus need water acquiring ingredients?).

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