How to keep your skin barrier strong, since it works like a brick wall

Key takeaways

• Your skin’s outer layer works like a brick wall: flattened cells are the bricks, and a mortar of ceramides, cholesterol and fatty acids in roughly equal numbers seals the gaps³⁴.
• Healthy skin is mildly acidic, and in a study of 330 volunteers, skin below pH 5 scored better for barrier function and moisture⁹.
• Soap, harsh detergents, dry air and heavy scrubbing wear the barrier down, while short warm showers and gentle cleansers help it hold up¹⁷¹¹¹⁵.
• Creams that pair ceramides with cholesterol and fatty acids, along with niacinamide (a form of vitamin B3), work with the barrier’s own chemistry¹⁰¹²¹³.
• In 12-week trials, adults taking flaxseed or evening primrose oil, or having high-flavanol cocoa or green tea, had less water loss through their skin⁶¹⁴.

Right now, a little water is drifting out through your skin and into the air. Scientists call it transepidermal water loss, or TEWL. It is the most widely used objective measure of how well your skin barrier is doing its job¹.

That barrier lives in the thin outer layer of your skin. Peter Elias and his colleagues at the University of California, San Francisco, spent decades working out its chemistry⁴¹⁰¹². Elias has since written guidelines for barrier creams built from the same fats the skin makes on its own².

The barrier is also renewing itself all the time, as new cells move up from below to replace the ones that shed³. So your daily choices at the sink, in the kitchen and in your supplement routine get a fresh chance to support it every day. Here is how the barrier works, what wears it down, and what research says helps it stay strong.

Your outer layer is built like a brick wall

The skin’s outer layer (stratum corneum) is made of flat, protein-packed cells called corneocytes. As these cells rise toward the surface, they lose their nuclei and most of their inner parts, so very little activity goes on inside them³. Scientists picture them as bricks.

The mortar is a layer of fats that the cells release as they mature³. This “brick and mortar” design slows water loss from the body and limits what can get in from outside³. Tiny protein rivets called corneodesmosomes hold neighboring bricks tightly together⁵.

The mortar follows a precise recipe. By weight, it is about 50% ceramides, 25% cholesterol and 15% free fatty acids, with very few phospholipids⁴. Counted molecule by molecule, those three fats show up in roughly equal numbers, a 1:1:1 ratio⁴⁵. They stack into thin, orderly sheets, and this fatty layer is the main hurdle that water must cross on its way out⁵.

Ceramides are waxy fats that give the mortar its structure. One special group, called acylceramides, carries linoleic acid, an essential fatty acid that has to come from food⁴⁶. The amount of linoleic acid in these ceramides tracks closely with how well the barrier works⁶.

Built-in moisture and a mildly acidic surface

The bricks come with their own moisturizer. Inside each corneocyte sits natural moisturizing factor (NMF), a mix of amino acids and related compounds, plus salts, sugars, lactic acid and urea⁷. NMF makes up about 10% of the mass of these cells and 20% to 30% of the outer layer’s dry weight⁷.

Most NMF comes from a protein called filaggrin. As cells travel toward the surface, filaggrin breaks down into small molecules that make up 70% to 100% of the outer layer’s free amino acids⁷. The single most common part of NMF is pyrrolidone carboxylic acid, known as PCA⁷.

Genes shape this system. About 1 in 11 people of European ancestry (roughly 9%) carry one of two common filaggrin variants⁷. Carriers have less NMF throughout the outer layer and lose more water⁷. The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) notes that gene changes affecting a key skin protein can let moisture escape⁸. Skin can then turn dry and damaged, a pattern NIAMS links to atopic dermatitis, a type of eczema with its own article in this library⁸.

The surface of healthy skin is also slightly acidic, a feature known as the acid mantle. A 2006 study tested 330 volunteers in the Netherlands, Germany, the Philippines and Spain⁹. Researchers checked forearm skin before and after 24 hours with no showering and no skin products⁹. The average pH dropped from 5.12 to 4.93, and the team estimated that skin’s natural resting pH is about 4.7⁹.

That acidity seems to matter. Skin with a pH below 5 scored better for barrier function, moisture and scaling than skin above 5⁹. In the same paper, acidic conditions helped the skin’s friendly resident bacteria stay put, while alkaline conditions made them scatter⁹.

Water loss is how scientists grade the barrier

The barrier’s main job is keeping water in, so scientists judge it by how much water gets out. A small probe rests on the skin and senses the change in water vapor just above the surface¹. Results come in grams of water per square meter per hour, and higher numbers point to a leakier barrier¹.

The readings are sensitive. Humidity, room temperature, air drafts, sweat and even the time of day can shift them¹. Researchers ask volunteers to rest for 20 to 30 minutes first, in rooms kept at about 64°F to 70°F with 40% to 60% humidity¹.

Water loss also differs across the body. It runs high on the palms, soles, armpits and forehead and low on the forearm and calf¹. That is why the inner forearm is the favorite test spot in barrier studies¹.

To study recovery, scientists sometimes weaken the barrier on purpose. They press tape onto the skin and peel it away, lifting off layers of cells, then track how quickly water loss returns to normal¹¹⁰. That recovery speed gives a clear picture of how well the skin rebuilds its wall.

Soap, harsh detergents, dry air and age wear it down

Your barrier is tough, but some everyday habits chip away at it. Washing is the one most of us do every day. Routine soap washing pulls NMF out of the upper layers of the skin⁷.

Washing also shifts pH. Plain tap water, which runs around pH 8 in much of Europe, raised skin pH for up to 6 hours in the 2006 study⁹. Soap had a longer effect, and skin washed with soap still had not returned to its starting pH after 6 hours⁹.

Harsh cleansers add to the strain. Strong detergents such as sodium lauryl sulfate (SLS) push water loss up¹. The American Academy of Dermatology (AAD) suggests a gentle cleanser, used only where needed¹¹. Use just enough to clean without making a thick lather¹¹.

Dry air matters too. When the air is humid, filaggrin breaks down into NMF near the skin’s surface⁷. In low humidity, the enzymes that do this job work poorly, which adds to dryness at the surface⁷. The AAD suggests running a humidifier, especially in the bedroom at night¹¹.

Scrubs and peels can go too far. Laser, chemical and mechanical methods can remove the outer layer, and doing so makes it easier for substances to pass into the skin¹⁵. Going easy on gritty scrubs and strong peels gives new cells time to take the place of the ones you remove.

Age plays a part. Older skin rebuilds its barrier more slowly after damage, partly because it makes less of the barrier fats, especially cholesterol¹⁰. NMF levels also fall with age⁷.

Irritation is the last piece. Chemical messengers released during skin inflammation turn down the enzymes that build long ceramides, which shifts the ceramide mix⁴. Barrier damage itself sparks more of these messengers, so a weak barrier and irritated skin can feed each other⁴.

Skin care that matches the barrier’s own recipe

Elias’s lab found that skin is picky about the fats you put on it. In studies of mouse and human skin, mixtures with only one or two of the three fats slowed normal recovery¹². Balanced mixtures of all three allowed it¹². A natural fat mixture with all three, plus phospholipids, helped tape-stripped human skin recover faster¹². It also raised moisture levels in both damaged and normal skin¹².

The ratio can be fine-tuned. Earlier studies in mice and in adults aged 20 to 30 found that a 3:1:1:1 mix, with one of the fats at triple strength, sped recovery¹⁰. A small 1997 study then tested six adults with an average age of 80¹⁰. A mix led by cholesterol helped their tape-stripped skin bounce back faster at the 6-hour mark¹⁰.

In a 2022 review, Elias recommended barrier creams that supply the three key fats at an appropriate ratio². On a label, that means looking for ceramides listed together with cholesterol and fatty acids. Moisturizers in general have their own article in this library.

Niacinamide, a form of vitamin B3, gives the skin’s own fat factories a nudge. In a lab study of human skin cells, it raised ceramide production 4 to 5.5 times and also increased free fatty acids and cholesterol¹³. When the same team applied niacinamide to dry skin, the outer layer held more ceramides and fatty acids, and less water escaped¹³.

Linoleic acid can work from the outside too. A classic study looked at people low in essential fatty acids⁶. Applying sunflower seed oil to the forearm daily for two weeks raised linoleic acid levels in their skin⁶. Water loss returned to normal and the skin looked less scaly, while people with normal fatty acid levels saw no change⁶. Plant oils are covered in more detail in their own article.

Daily habits round out the picture. This checklist comes from AAD guidance and the research above:

• Keep baths and showers to 5 to 10 minutes, using warm water¹¹

• Choose a gentle cleanser and use it only where you need it¹¹

• Pat skin dry with a clean towel instead of rubbing¹¹

• Apply moisturizer while your skin is still damp, and favor creams or ointments over thin lotions¹¹

• Run a humidifier at night and clean it regularly¹¹

• Go easy on scrubs and peels so the outer layer has time to renew¹⁵

Foods and supplements that support the barrier from within

Because linoleic acid is built right into the barrier’s ceramides, what you eat feeds the wall directly. When people do not get enough essential fatty acids, their skin turns scaly and water loss climbs⁶. In a national U.S. nutrition survey (NHANES I), women aged 40 to 74 who ate more linoleic acid were less likely to have dry or thinning skin⁶. Sunflower and safflower oils are rich sources⁶.

Oils in capsule form have been studied too. In a 12-week trial, 45 women aged 18 to 65 with dry, sensitive skin took 2.2 grams a day of flaxseed oil or borage oil, or a placebo⁶. Both oil groups had less water loss, roughness and scaling than the placebo group⁶. Their skin also reacted more mildly to a test irritant⁶.

In another 12-week trial, 40 healthy adults aged 32 to 56 took either 1.5 grams of evening primrose oil a day or a placebo⁶. The evening primrose group scored better for moisture, water loss, elasticity, firmness and roughness⁶. Evening primrose and borage oils are rich in gamma-linolenic acid (GLA), while flaxseed oil supplies the plant omega-3 called ALA⁶.

Plant compounds called flavanols show up in this research as well. In a 12-week trial of 24 young women, those who had cocoa with 326 milligrams of flavanols a day saw smoother skin and less water loss¹⁴. A comparison group whose cocoa had only 27 milligrams of flavanols saw no change¹⁴.

Green tea has a similar story. A 12-week trial included 60 women aged 40 to 65¹⁴. Those who drank a daily liter of green tea beverage, supplying 1,402 milligrams of catechins, scored better than placebo for water loss, roughness, scaling and elasticity¹⁴.

Vitamin C may help as well. In lab studies of skin cells, vitamin C helped the cells make barrier fats and form a barrier¹⁵. In a large nutrition survey, higher vitamin C intake from food went along with less dry skin¹⁵.

Vitamin E takes a scenic route. It collects in the skin’s oil glands and rides to the surface in sebum¹⁶. There it settles into the fatty mortar of the outer layer and adds antioxidant protection¹⁶. After you take in more vitamin E, it takes at least seven days for the level in sebum to change¹⁶.

Ingredient	How it was used	What it does	What research found
Ceramides, cholesterol and fatty acids	Cream on the skin	Matches the barrier’s own fat recipe	Faster recovery of tape-stripped human skin1012
Niacinamide (vitamin B3)	Applied to the skin	Helps skin cells make ceramides	More ceramides and less water loss in dry skin13
Sunflower seed oil	Applied daily for 2 weeks	Supplies linoleic acid	Water loss back to normal in people low in essential fats6
Flaxseed oil	2.2 g a day by mouth, 12 weeks	Supplies the omega-3 ALA	Less water loss and roughness than placebo in a trial of 45 women6
Evening primrose oil	1.5 g a day by mouth, 12 weeks	Supplies GLA	Better moisture and water loss scores in a trial of 40 adults6
Cocoa flavanols	326 mg a day, 12 weeks	Plant compounds	Less water loss in a trial of 24 women14
Green tea catechins	1,402 mg a day in a drink, 12 weeks	Plant compounds	Better water loss and roughness scores in a trial of 60 women14

Sources:^610121314

Smart use: amounts, quality and patience

The amounts in these studies give you a practical starting point. Researchers used 2.2 grams a day of flaxseed oil, 1.5 grams a day of evening primrose oil, and 326 milligrams of cocoa flavanols⁶¹⁴. The green tea study used a daily drink rather than pills¹⁴. For linoleic acid, everyday foods such as sunflower and safflower oils are a simple place to start⁶.

Quality matters with any supplement. Look for a third-party seal such as USP Verified, NSF Certified for Sport or ConsumerLab approved. These seals tell you an independent lab checked that the product contains what the label says.

Give your skin time. Every supplement and food trial above ran for 12 weeks, and the outer layer renews itself gradually as new cells rise from below³⁶¹⁴. Plan on 8 to 12 weeks of steady use before you judge the results.

Share your full supplement list with your doctor or pharmacist so everything works together, especially if you take prescription medicines or manage a health condition. For new skin products, a simple patch test on a small area is a smart first step. Patch testing has its own article in this library.

The bottom line

Your skin barrier is a living wall. Flat cells stack like bricks, and a balanced mortar of ceramides, cholesterol and fatty acids seals them³⁴. A built-in moisturizer and a mildly acidic surface keep the whole system working⁷⁹. Scientists grade it by how little water slips out¹.

Supporting that wall is mostly about steady, gentle habits. Keep showers short and warm, choose mild cleansers, add moisture to the air, and pick creams that echo the skin’s own fat recipe²¹¹. Niacinamide gives the skin’s ceramide production a lift in research, and linoleic acid supports the barrier from both the outside and the inside⁶¹³.

Your plate and your supplement shelf can help too. Foods rich in linoleic acid feed the barrier’s ceramides⁶. Flaxseed oil, evening primrose oil, cocoa flavanols and green tea all have encouraging 12-week studies behind them⁶¹⁴. Give any new routine about three months, the same span those trials used, so your skin has time to respond.

Sources

1. Alexander H, Brown S, Danby S, Flohr C. Research Techniques Made Simple: Transepidermal Water Loss Measurement as a Research Tool. Journal of Investigative Dermatology. 2018. pubmed.ncbi.nlm.nih.gov

2. Elias PM. Optimizing Emollient Therapy for Skin Barrier Repair in Atopic Dermatitis. UC San Francisco Previously Published Works (eScholarship, University of California). 2022. escholarship.org

3. Michels AJ. Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2011, updated 2026. lpi.oregonstate.edu

4. Feingold KR, Elias PM. The Role of Ceramides in the Disruption of the Cutaneous Permeability Barrier, a Common Manifestation of Skin Disorders. Journal of Lipid Research. 2024. pmc.ncbi.nlm.nih.gov

5. Schmitt T, Neubert RHH. State of the Art in Stratum Corneum Research. Part II: Hypothetical Stratum Corneum Lipid Matrix Models. Skin Pharmacology and Physiology. 2020. pmc.ncbi.nlm.nih.gov

6. Angelo G. Essential Fatty Acids and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2012, updated 2026. lpi.oregonstate.edu

7. Fowler J. Understanding the Role of Natural Moisturizing Factor in Skin Hydration. Practical Dermatology. 2012. practicaldermatology.com

8. National Institute of Arthritis and Musculoskeletal and Skin Diseases. Atopic Dermatitis. National Institutes of Health. Accessed 2026. niams.nih.gov

9. Lambers H, Piessens S, Bloem A, Pronk H, Finkel P. Natural Skin Surface pH Is on Average Below 5, Which Is Beneficial for Its Resident Flora. International Journal of Cosmetic Science. 2006. pubmed.ncbi.nlm.nih.gov

10. Zettersten EM, Ghadially R, Feingold KR, Crumrine D, Elias PM. Optimal Ratios of Topical Stratum Corneum Lipids Improve Barrier Recovery in Chronologically Aged Skin. Journal of the American Academy of Dermatology. 1997. pubmed.ncbi.nlm.nih.gov

11. American Academy of Dermatology. Dermatologists’ Top Tips for Relieving Dry Skin. AAD.org. 2026. aad.org

12. Man MQ, Feingold KR, Wang F, Thornfeldt CR, Elias PM. A Natural Lipid Mixture Improves Barrier Function and Hydration in Human and Murine Skin. Journal of the Society of Cosmetic Chemists. 1996. library.scconline.org

13. Tanno O, Ota Y, Kitamura N, Katsube T, Inoue S. Nicotinamide Increases Biosynthesis of Ceramides as Well as Other Stratum Corneum Lipids to Improve the Epidermal Permeability Barrier. British Journal of Dermatology. 2000. pubmed.ncbi.nlm.nih.gov

14. Angelo G. Flavonoids and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2012, updated 2026. lpi.oregonstate.edu

15. Michels AJ. Vitamin C and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2011, updated 2026. lpi.oregonstate.edu

16. Michels AJ. Vitamin E and Skin Health. Micronutrient Information Center, Linus Pauling Institute, Oregon State University. 2012, updated 2026. lpi.oregonstate.edu

This article is for general education and is not medical advice. Talk with your healthcare professional about your own health, especially before starting a new supplement if you are pregnant, nursing, taking medicine, or managing a health condition. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Reviewed October 2026.