The skin barrier sounds like a simple concept but is actually quite complex when you get into the details. There are a lot of parts that go into making it function properly, and each of those parts works with the others to strengthen the skin. One such part is something called the "moisture barrier." But what exactly is that, and how does it relate to the larger skin barrier? This is where it takes a bit of nuance.
In the past, we've talked about the skin barrier as something of a "brick and mortar" visual—and while this isn't entirely inaccurate, it's not the whole picture.
"We were taught initially that the skin barrier is this brick and mortar. The bricks are dead skin cells, and the mortar is the fat. It's almost like a wrap around the body. And just in the last couple of years, we know that it's so much more dynamic than that," says board-certified dermatologist and mbg Collective member Whitney Bowe, M.D. Your barrier is not just a simple brick wall: It's a living, dynamic defense system with several commingling teams and players. And to understand the moisture barrier, you need to understand all that works with it and around it.
What is the moisture barrier?
The moisture barrier is an outer layer of skin that ensures your skin is hydrated by trapping and holding water. One of the ways your skin dries out is when water escapes your barrier and evaporates into the air around you—or what's called transepidermal water loss. So keeping that moisture layer strong is essential to overall skin function.
So what makes up this moisture barrier? A combination of proteins from dead skin cells and lipids. To go back to the brick-and-mortar analogy I alluded to in the introduction, if there was a part of the skin that resembled the brick wall, it'd be this. (I told you it wasn't an entirely inaccurate visual!) The proteins are things like collagen and keratin, and the lipids are your skin's natural oils and waxes (sometimes collectively called the lipid layer), such as squalene and ceramides. To get technical, this moisture barrier is called the stratum corneum—and when you look at renderings of the skin, you'll see it's the outermost layer of the epidermis.
How does it relate to the skin barrier?
To contextualize this moisture barrier (or stratum corneum, which I'll use interchangeably from here on out now that we've established what they are), we must understand the skin barrier writ large. The barrier isn't only this brick-and-mortar part, as we once thought. "There are actually four main components to the skin barrier," says Bowe. "It also contains components such as the skin microbiome, acid mantle, and the skin's own immune system."
Let's break it down:
- The moisture barrier (or stratum corneum) is the outermost layer of the skin and is made up of lipids and proteins. This is the layer that keeps in hydration.
- The skin microbiome is the trillions of microorganisms that reside on and in our skin. The skin microbiome is highly complex in itself but greatly contributes to overall skin and body health.
- The acid mantle is the thin, slightly acidic film that covers the skin. It is a mixture of your natural sebum (oil) and sweat. The pH range of the skin on your face and body fluctuates between 4.7 and 5.751.
- The skin's immune system2 (yes the skin has its own immune system) incorporates elements from all of the above, as well as skin resident immune cells and free radical fighters (like antioxidants).
All these parts work together to fortify and support each other. For example, the skin microbiome is able to help produce byproducts (called postbiotics) such as lipids and peptides to feed back into the stratum corneum. On the flip side, when one is weak, it can hinder the rest. For example, if the acid mantle is disrupted, it can change the microflora of the biome or strip the moisture barrier of lipids.
And why is it so vital to tend to all these parts? Because a strong skin barrier literally means a better protected body. "It protects us from mechanical injury, low humidity, cold, heat, sun, wind, chemical exposure, bacteria, viruses, fungi, and other pathogens," explains board-certified dermatologist Hadley King, M.D., stating that, "a healthy barrier is critical to normal skin function."
As with most things in health: Knowing the full, robust structure of the barrier can help us better understand how to help and care for it.
How does it become damaged?
A lot can affect the moisture barrier—from things in your control to elements well beyond. You'll notice that your barrier has become compromised or weakened if it's easily irritated, inflamed, burns, or reacts to things that it used to tolerate. Here are the main components to be mindful of when tending to the moisture barrier.
- Harsh soaps & hot water. Much of the damage to the moisture barrier happens in the shower or wash: Sulfates and strong soaps strip the skin of its oils and damage the proteins. Hot water can also dissolve the skin's protective oils.
- Overexfoliation. Exfoliation is the act of removing dead skin cells from the stratum corneum. Doing this to a degree is a good thing, as it can make the skin appear vibrant and encourage cell turnover—but when you go overboard, you're removing those precious proteins and lipids that make up the outer layer of the skin.
- Lifestyle habits. Not staying hydrated internally has been shown to affect the skin's dermal density. Additionally, things like consuming drying liquids (caffeine, alcohol) can contribute to internal dehydration. Finally, things like smoking can harm the barrier.
- Sun exposure and pollution. Environmental stressors bombard the skin with free radicals and oxidative stress.
- Skipping hydrating topicals. If you forget to apply face cream or body lotion post-shower or wash, that will do a number on the barrier and contributes to transepidermal water loss.
How to care for your barrier?
The good news is that even though there are several things that can damage the barrier, it's a resilient system and can spring back to good health with some care and attention. And as we've noted, the skin barrier and moisture barrier are complex systems—so nurturing them will take a well-rounded approach. You'll notice your moisture barrier is healthy when it's bright, supple, feels hydrated, and is resilient to most changes. Here, some of the top ways to help your moisture barrier:
Hydrate with smart topicals.
A well-formulated hydrator will do wonders for your skin and moisture barrier. Look for options with a robust assortment of moisturizing botanicals and lipids to feed that lipid layer. There are many solid ingredients out there, so just look for those you like the texture and appeal of. A few to keep in mind: Aloe vera is a lightweight humectant, shea butter is a rich fatty-acid-filled butter, oat oils and extracts are ideal for sensitive skin, or squalane works well with your skin's natural oils.
Additionally, we recommend looking for options that not only treat the moisture barrier but also tend to the other areas of the skin barrier. Biotic ingredients can feed and nurture your skin's microflora, helping support the balance, calming the skin, and improving the overall health of your skin. Antioxidants—like vitamin C, E, coenzyme Q10, and fruit extracts—can support your skin's immune system and neutralize free radicals. Finally, make sure you're using a formula that keeps your pH relatively stable, so as not to disrupt the acid mantle.
Adjust lifestyle habits if needed.
We can't avoid all external stressors, and we'd never recommend you try. But you can make habit tweaks to ensure you're helping your skin deal with the onslaught of free radicals that come with these stressors. First up, stop smoking (full stop!). Also, do your best to drink your fill of water and balance dehydrating liquids. Be mindful of your sun exposure by wearing mineral sunscreen, avoid excessive sunbathing and exposure, and cover up with sunglasses, hats, and appropriate clothing if you're going to be in direct sunlight.
Support your skin's proteins and lipids internally.
Given your moisture barrier is made up of proteins from skin cells and lipids, feeding your body a supporting supply of them can help your overall skin health. Look for collagen-containing foods, a wide variety of healthy fats, and of course skin-supporting antioxidants. All of these can support your skin barrier from the inside out.
If you want extra help, collagen supplements contain amino acids (the building blocks of proteins) and can help the body produce its own collagen. Or you can look for skin supplements with lipids like phytoceramides or healthy fats like omega-3s.
Your moisture barrier is a critical part of the overall skin barrier function, and to care for one part means to care for all. The moisture barrier itself (also called the stratum corneum) is the layer made up of proteins and lipids that traps in water and keeps all below it protected. While it can become damaged by harsh topicals and outside stressors, you can care for it with smart topicals and lifestyle habits. If you want to learn more about how to care for your skin barrier function overall, check out our guide.
Alexandra Engler is the beauty director at mindbodygreen and host of the beauty podcast Clean Beauty School. Previously, she's held beauty roles at Harper's Bazaar, Marie Claire, SELF, and Cosmopolitan; her byline has appeared in Esquire, Sports Illustrated, and Allure.com. In her current role, she covers all the latest trends in the clean and natural beauty space, as well as lifestyle topics, such as travel. She received her journalism degree from Marquette University, graduating first in the department. She lives in Brooklyn, New York.