What Is Your Skin Barrier, and Why Should You Protect It?

Written and Reviewed by: Elysium Health

skin barrier function

Key Takeaways:

  • The outer layer of your skin faces the world and protects you from it by limiting water loss, blocking harmful substances from entering your body, and preventing infections. Taken together, these tasks are known as barrier function.
  • Barrier function is not only essential for your overall health, it is strongly correlated with skin appearance.
  • Barrier function can be negatively affected by aging, environmental factors, and harsh skin care practices.
  • You can help maintain a healthy barrier function with proper skin care and by supporting your skin’s natural regenerative processes.

Related Products:

  • Mosaic: Developed with the advisement of Dr. Granstein, a world-renowned dermatologist, Mosaic is a daily softgel that combines hyaluronic acid with carotenoids to increase skin moisture, reduce water loss, improve resilience against stressors, and help maintain collagen and elastin production to support a healthy skin barrier for visibly youthful skin. 
  • Basis: Clinically proven to raise NAD+ levels by 40%, Basis supports ceramide and collagen production, in addition to hundreds of other cellular processes for healthy skin and healthy aging.

What is the skin barrier?

Your skin is composed of three layers: the epidermis, dermis, and hypodermis. These layers differ significantly from each other in structure and function. The epidermis is the body's first line of defense and creates a barrier between the inside and outside of the body. Its main functions are to limit water loss, block harmful substances from being absorbed, and prevent infections.

Epidermal layers

Figure 1. Layers of the skin


The epidermis is made up of five sub-layers formed through a process called keratinization, where skin cells (keratinocytes) grow and mature. The outermost layer of the epidermis (the stratum corneum) is made of corneocytes—dead, differentiated keratinocytes filled with the protein keratin—embedded in a matrix of lipids (fats) like ceramides, cholesterol, and free fatty acids. The cells and lipids in the stratum corneum (SC) are arranged in a “brick and mortar” pattern and play an essential role in forming the skin barrier by preventing excessive loss of water, ions, and proteins.

the stratum corneum structure

Figure 2. Brick and mortar structure of the stratum corneum

Why is skin hydration essential?

Water naturally evaporates through the skin into the external environment due to differences in water vapor pressure gradients. This is a normal process and it’s called transepidermal water loss (TEWL). TEWL is used as an objective measurement of skin integrity, specifically the amount of water lost across the SC. Excessive TEWL, however, can lead to skin dryness, redness, and irritation, and can be detrimental to skin health. It’s both a cause and result of impaired barrier function.

healthy versus impaired skin barrier

Figure 3. Healthy versus impaired skin barrier

How the skin stays hydrated

Maintaining skin hydration is regulated by natural hygroscopic agents like hyaluronic acid (HA) or hyaluronan in the corneocytes that absorb moisture from the air. HA is capable of binding over 1,000 times its weight in water and plays a critical role in retaining moisture. Skin hydration also depends on the orderly arrangement of extracellular lipids (like ceramides) that form a barrier to water loss. Interestingly, HA also interacts with keratinocytes to regulate lipid synthesis and keratinocyte differentiation (the process by which the different sub-layers of the epidermis are maintained). 

Factors that impact skin hydration

Various factors can impact TEWL and skin hydration. Genetics and aging play a role but environmental and lifestyle factors can have a significant impact:

  • Aging and the decline of HA, ceramides, and collagen

As we age, our skin produces less HA. By age 60, we have half as much HA in the epidermis compared to our 20s. Like HA, all major lipid species, especially ceramides, also decrease in the SC, contributing to decreased hydration, volume, plumpness, and impaired barrier function. Aging is also accompanied by a reduction in collagen levels caused by a combination of degradation and reduced synthesis, resulting in decreased skin elasticity, reduced water content in the SC, and increased TEWL.
  • Environmental factors

Sun exposure, seasonal variations in temperature, and low humidity all contribute to decreased skin hydration. Solar UV radiation disrupts the skin’s barrier function, allowing moisture to escape more easily. Chronic UV exposure also leads to accelerated skin aging, resulting in a thinner epidermis and decreased ability to retain moisture. Seasonal climate can also affect skin hydration: lipid levels decrease in winter, contributing to disruptions in barrier function, while hot temperatures increase sweating and upregulation of skin pores. Humidity also plays an important role, with low humidity causing inflammation, dysregulated proliferation of epidermal cells, and increased TEWL.
  • Advanced glycation products (AGEs)

AGEs are proteins or lipids that become modified (glycated) as a result of exposure to sugars. The accumulation of glycated products in the epidermis is associated with decreased water content in the SC, skin dryness, and barrier disruption. AGEs can accumulate in the skin as a byproduct of normal metabolism and aging and external sources. Sugary foods, highly processed foods, and animal-derived foods cooked at high temperatures are high in AGEs.
  • Circadian rhythm and time of day

Several properties of the skin are subject to circadian variations, including skin temperature, permeability, pH, and sebum production. Skin permeability and TEWL are reported to be highest in the evening when we are sleeping and lowest in the morning.
  • Skin conditions

Conditions like eczema, psoriasis, and rosacea cause inflammation and damage to the skin, impacting the skin’s barrier function and hydration.
  • Aggressive skin care practices

Over cleansing, use of harsh skin care products, such as those containing alcohol or strong chemicals, and over-exfoliation can strip the skin of its natural oils and cells, and cause the barrier to weaken over time, impacting its ability to lock in moisture effectively.

What does excessive TEWL look like?

Excessive moisture loss, if not cared for, can lead to impaired barrier function and dry skin. Here’s a closer look at how excessive moisture loss can affect your skin:

  • Breakouts

Excessive TEWL can lead to dry, dehydrated, and irritated skin, and impaired barrier function, making it more susceptible to breakouts, including acne.
  • Loss of elasticity

Consistent, prolonged TEWL due to damage to the skin barrier or exposure to environmental factors can lead to skin dehydration, which in turn leads to a loss of elasticity. Wrinkles become more likely given that skin is less capable of bouncing back from creasing and folding.
  • Collagen and elastin breakdown

These proteins help structure the skin. Prolonged water loss, especially alongside sun exposure, can accelerate the breakdown of collagen and elastin fibers. The skin loses its ability to maintain a smooth and wrinkle-free appearance.
  • Dry skin

Dry skin is subject to becoming flaky and rough, and more prone to creasing and wrinkling. This happens in particular in areas of repetitive movement, like around the eyes and mouth. Feelings of tightness and discomfort also accompany excessive TEWL.
  • Impaired repair mechanisms

Excessive TEWL can interfere with the skin's natural repair mechanisms. 

What can I do about excessive water loss?

We can target excessive water loss by controlling external factors (like our environment) and by supporting natural hydrating processes inside the skin. External methods include the use of a humidifier, especially at night when our skin is the most permeable, to reduce overnight TEWL. We can also protect our skin from sun exposure with regular use of sunscreen (up to 90% of visible changes to the skin can be attributed to photoaging or chronic sun exposure). Topical moisturizers can also provide immediate hydration and relief from dryness. However, their use is limited to the area of application and the outer surface of the skin. 

There is a growing body of evidence demonstrating the benefits of oral supplements for hydrating the skin from the inside and for stimulating biological processes in the skin to help maintain a healthy skin barrier. In particular, ingredients that support ceramide and collagen production and boost naturally occurring hygroscopic agents in the skin are shown to help maintain a healthy skin barrier and stave off excessive TEWL. Here are some of the science-backed ingredients that have been demonstrated to support skin health and barrier function through oral administration.

  • Hyaluronic acid, the body’s natural moisturizing agent

HA is a popular hydrating ingredient in topical moisturizers, serums, and masks. It’s also a common ingredient in dermal injections or fillers, but what you may not know is that oral supplementation with HA is clinically proven to increase skin moisture content, improve dry skin, decrease TEWL, and reduce the appearance of fine lines and wrinkles. Ingested HA reaches the skin, where it can provide moisturizing effects from the inside out. In addition, the benefits of oral HA extend across the entire body, unlike topical products and fillers that only affect the area of application.
  • NAD+ precursors

Ceramides and other lipids in the skin decrease naturally with age, but there are ways to stimulate their production, including supplementing with precursors of NAD+. Studies demonstrate that niacinamide (also known as nicotinamide or NAM) stimulates the synthesis of ceramides and other lipids in the SC and reduces TEWL. NAM is one of several precursor molecules that contribute to the synthesis of NAD+, a critical coenzyme that’s present in all of our cells and whose level also declines significantly with age—NAD+ levels in the skin decline by as much as 50% every 20 years.
  • Carotenoids

Carotenoids are yellow, orange, and red pigments synthesized by plants and, when ingested, accumulate in our skin and provide antioxidant benefits. Environmental challenges and oxidative stress can lead to collagen degradation in the skin, contributing to skin aging and weakening of the barrier. Studies demonstrate that carotenoids can neutralize free radicals, which can degrade collagen, and stimulate pro-collagen levels in cultured dermal fibroblasts exposed to oxidative stress.

Some simple steps for more youthful-looking skin

So now we know there are some science-backed ways to combat excessive moisture loss and maintain a healthy skin barrier. Our daily skin supplement, Mosaic, offers a new step in your skincare routine that works with your natural regenerative processes and drives changes from the inside. Developed under the advisement of Dr. Granstein, a world-renowned dermatologist and Chair of the Department of Dermatology at Weill Cornell Medicine for over 30 years, Mosaic is formulated with hyaluronic acid and a unique Phytonutrient Carotenoid Complex to restore moisture, elasticity, and help maintain natural levels of collagen and elastin. Our NAD+ supplements Basis and Signal provide highly efficient precursors to NAD+ (more efficient than NAM), to counter the age-related decline in NAD+ levels and support ceramide and collagen production for healthy skin.

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The Skin Benefits of Carotenoids

Carotenoids are pigments synthesized by plants, and they are fundamental to our health—especially our skin. Read on to learn about how carotenoids benefit our skin and how to obtain more carotenoids in our diet.