Skin hydration is a topic that is discussed often yet somehow the importance is still overlooked. We often hear that the benefits are only temporary and that at most, it offers a transient brightening or plumping effect to the skin. In this follow-up to my 3 part Instagram series on hydration, I will be taking a closer look at skin anatomy and physiology as it relates to hydration, the benefits that hydration has, and how to apply this to your skincare routine and treatments.
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Factors Influencing Skin Hydration
Skin Anatomy and Physiology
To understand how the skin remains hydrated, we have to understand the anatomy of the skin. Particularly, the skin barrier. The “brick and mortar” skin model is often used since it’s simple and easy to understand.
As a quick refresher, the skin has 2 layers: the epidermis and the dermis. The subcutaneous layer is not part of the skin which is why college medical courses have moved away from calling it the hypodermis.
If you’ve ever taken a medical language course, “hypo” and “epi” are both medical prefixes. Since epidermis loosely translates to “over dermis,” hypodermis meaning “below dermis” could be assumed to be part of the skin too. So now it’s called the subcutaneous layer. There’s your random fact of the day for my fellow skincare science nerds.
As you can see below, the dermis is the deeper skin layer and made up of the reticular dermis at the bottom and the papillary region above. The epidermis is the superficial skin, or the skin we can see, and it’s broken up into 4 layers except for areas of the body with thick skin (like your palms) which has an additional layer called the stratum lucidum.
In this post, we will be focusing only on the very uppermost layer of the epidermis. This top layer is called the stratum corneum and is where our skin barrier can be found. This is why in addition to epidermal barrier, you’ll hear it referred to as the stratum corneum barrier. Just don’t call it your “moisture barrier,” that’s not an actual term.
Comment below if you’re interested in continuing to learn more on skin anatomy!
In the meantime, if you’re looking to learn more on your own I highly recommend reading the Medscape CME course the above image is from. You can find it here and while it’s for clinical dermatologists, it’s easy to understand and very thorough.
The stratum corneum is technically dead. Skin cells called ketatinocytes begin their lives as stem cells in the stratum basale and differentiate and move outward during a process you may have heard called “cell turnover.” By the time keratinocytes reach the stratum corneum, they’re dead yet still serve important functions. For example, some keratinocytes differentiate into corneocytes which are the “bricks” in the brick and mortar skin model while and lipids are the “mortar.”
We often think of sebaceous lipids (aka sebum) from our sebaceous glands as being mainly responsible for keeping skin moisturized. But it’s actually the skin barrier lipids, which are produced by keratinocytes at the surface of the skin, that act as the “mortar.” They’re made up of ceramides, cholesterol, and fatty acids primarily and they’re absolutely vital to the structure and function of the skin barrier. When lipids are depleted or disorganized, the integrity of the skin barrier is impacted and we see more trans epidermal water loss (TEWL). Since the skin barrier is also designed to keep microorganisms out, altered skin barrier function is detrimental in other ways too.
The “bricks,” or skin cells called corneocytes, are bridged together by junctions called corneodesmosomes. Inside the corneocytes is where you’ll find the skin’s Natural Moisturizing Factor. The NMF is the naturally occurring humectants in our skin, made up of amino acids, urea, PCA, lactic acid, glycerin, high molecular weight hyaluronic acid, and more. They attract and bind moisture and then draw it into the corneocytes. So while the skin barrier is responsible for keeping moisture inside the skin, it’s the role of the NMF to maintain skin hydration and it also helps keep the stratum corneum flexible.
Dead or not, the stratum corneum is still very biochemically active. Hydration of the skin is key for the health of the stratum corneum as well as for the hydrophilic enzymes required for desquamation (shedding of dead skin cells). Better hydration even loosens the junctions between cells which opens temporary pores and makes the skin more permeable for added penetration of ingredients. But this will come up more later, don’t worry.
Environmental Hydration Factors
Now that we’ve covered how the skin maintains its hydration, you’ll better understand why external and internal factors can easily disrupt this. First, the external.
Because the skin barrier is the most superficial layer of our skin, it’s under constant assault from its environment. This makes the skin barrier and hydration easily influenced by things like weather and harsh cleansers. When skin barrier lipids are depleted or disordered, barrier function suffers. Skin surface pH and micro flora are also important to skin health.
Environmental Factors Detrimental to Skin Health:
- harsh detergents. Bar soaps and sulfates are often too harsh for the skin, stripping it of moisture and lipids. Because they’re high in pH, they also raise the surface pH of the skin from its acidic state which can promote dispersal of flora from the skin.
- Long hot showers and baths
- Indoor heating and air conditioner can cause very dry air
- Extreme weather conditions like very cold, windy, or snowy weather
Intrinsic Hydration Factors
Hydration levels are also greatly impacted by internal factors and processes in the skin.
First though, let’s touch on something that isn’t really a factor – oral intake of fluids.
The rest of the body’s hydration has less impact on the hydration of your skin than you would think. When I suggest to someone that they improve the hydration of their skin, I often hear “I’ll drink more water.” As long as you’re not dehydrated, drinking more water will not improve skin hydration in a significant way.
This is because tissue in the body is rehydrated via circulation and only the dermis is vascular. The epidermis has to rely on diffusion from the moisture rich dermis and on the skin barrier and NMF for hydration. Because of this, you’re much better off targeting the skin specifically by applying topical humectants to draw moisture where it’s needed – the epidermis – and help moisture loss from occurring.
Intrinsic Hydration Factors
- Aging. As we get older, hydration and hyaluronic acid especially declines in the epidermis. Decreasing estrogen especially means less lipid production as well as less production of hyaluronic acid.
- Skin disorders. Inflammatory skin disorders in particular are known for disordering skin barrier lipids, resulting in a loss of barrier function and moisture.
Benefits of Better Hydration
Now onto the actual benefits of keeping your skin barrier functioning well and your skin hydrated. By the way, can you count how many times I’ve said the word hydrated or hydration so far? Just don’t make it a drinking game.
We know that there are short term benefits to improving hydration. I think most of you probably are aware that using topical humectants like hyaluronic acid that increase the water content of the skin can have a temporary plumping effect that can decrease wrinkle depth and increase firmness and elasticity.
But did you know that light interacts with hydrated skin differently?
The appearance of the skin is a result of the way it interacts with light. Visible light interacts with skin by absorption and reflection. Chromophores are responsible for absorbing light – melanin is the main one in the epidermis while hemoglobin is the most common chromophore in the dermis. Light is also reflected at each layer of the skin.
When you increase the hydration of the skin, you change the way light interacts with it. More hydrated skin corresponds with a decrease in light reflection in the stratum corneum which means deeper penetration of light into the dermis. It also makes the skin more translucent.
Interestingly, the way the light interacts with our skin changes with age just like epidermal hyaluronic acid and hydration in general decreases with age. Younger skin reflects light more evenly and more intensely in the deeper skin while older skin still reflects light the same as younger skin in regards to the skin surface.
The above really makes me wonder if hydration helps penetration of light based treatments like Red Light Therapy and it’s something I will research further.
As we learned in the earlier section on skin barrier anatomy and function, skin hydration regulates many processes in the stratum corneum and its overall health. The hydrolytic enzymes responsible for desquamation (shedding of dead skin cells) are influenced by hydration as is the differentiation of corneocytes. This means for skin to optimally go through the process of turnover and shedding, it must properly maintain its moisture levels.
The above also applies to wound healing. We know that better skin hydration means faster wound healing and this may be able to be applied to resolving skin concerns like acne and hyper pigmentation quicker. What I think is especially of note though is that research indicates that hydration regulates proinflammatory genes. The article noted that not only does better hydration lead to better healing but that “decreased levels of hydration resulted in an increased expression of proinflammatory genes in human ex vivo skin culture (HESC) and stratified keratinocytes.”
In conclusion, focusing on hydration in your skincare routine is an important consideration for not only the person dealing with skin concerns like hyper pigmentation but those wanting the best results possible from microneedling and chemical peels.
Skin Conductivity and Permeability
Believe it or not, there’s still more benefits to properly hydrated skin.
On top of benefits like better healing post-microneedling and peels (and maybe even improved penetration for photobiomodulation possibly), it can achieve better treatment outcomes for most treatments that involve applying a current to the skin. The skin is the rare tissue in the body that’s very resistant to electrical current and treatments like microcurrent and radio frequency will be less effective if the current isn’t getting past the skin and where it needs to go – especially since RF follows the path of least resistance. Research wise, conductivity increases with uptake of water so you can get more out of your treatments by making sure your skin is hydrated.
An uptake in water is also linked to better permeability. Remember those corneodesmosomes we talked about, the junctions between the corneocytes in our skin barrier and that are crucial for stratum corneum cohesion? When water content in the skin is increased, it creates pores between those cell junctions and makes the skin barrier more permeable.
Of course, a long term increase in permeability wouldn’t be a good thing as it could allow in microorganisms and other damaging things into the skin. Thankfully, studies show it’s a temporary effect that applies to larger molecules too. Skincare wise, this is promising for ingredients like peptides and growth factors that are normally too large to get past the skin barrier fully.
How to Improve Hydration
If you’ve stuck with me to this very last part of our deep dive, THANK YOU! At this point, you’re likely wondering how to best increase the hydration of the skin. And that’s exactly what the ending to this post will consist of – the best ingredients to look for as well as product recommendations.
How to Support Barrier Function and Increase Skin Hydration Levels
We have 2 main goals here: stopping moisture and lipid loss to begin with and increasing hydration.
We can do that the following ways:
- Use a low pH cleanser with gentle surfactants that ideally doesn’t foam. The more we minimize disruption to the skin, the better it will function.
- Consider a humidifier. If you’re dealing with dry air due to indoor heating or air conditioning, running a humidifier at night can really help mitigate some of the impact on the skin.
- Use an occlusive moisturizer. This will reduce trans epidermal water loss (TEWL) from the skin and stop the water based steps you’ve applied prior from evaporating from the surface of the skin.
- Include skin replenishing lipids and barrier supporting ingredients. Ceramides, cholesterol, and fatty acids can help if your skin barrier has depleted or disorganized lipids which will help the skin barrier function better. Ingredients like niacinamide, panthenol, urea, and allantoin can help the skin barrier and overall stratum corneum health.
- Apply humectants from our NMF and ingredients that increase our skin’s naturally occurring humectants. I find NMF humectants like glycerin, HMW HA, urea, lactic acid, amino acids, and sodium PCA to work especially well at hydrating skin and ingredients like glucuronic acid, N-Acetyl Glucosamine, HA coated gold particles, and hydroxyprolisilane can potentially increase hydration levels in the skin vs the temporary effects of topical humectants.
- Introduce a gentle, hydrating AHA. Alpha Hydroxy Acids like lactic acid and glycolic acid are humectants themselves and help hydrate but exfoliating will also allow better penetration of your other ingredients so they’ll work better.
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I truly hope that was helpful! It took a lot of time to research and put together so please comment or share if it was informative. Thank you!