Article: Occlusives, emollients, and humectants: which does a compromised barrier need?
Occlusives, emollients, and humectants: which does a compromised barrier need?
A compromised barrier needs its own lipids replaced and its water loss slowed, not stopped. Emollients built from the same fats the barrier is made of do the first job, and a partial occlusive does the second. Humectants add water only when something holds it in place, so on a damaged barrier they belong under a lipid.
Moisturizers fall into three classes by how they work. An occlusive is a material that forms a water-repellent film over the skin and physically blocks water from evaporating through it. A humectant is a material that attracts water and pulls it into the outer skin from the living layers beneath and, in humid air, from the surrounding air. An emollient is a lipid or oil that fills the spaces between the dead surface cells and leaves the skin softer and smoother [1]. Most products combine all three, and most single materials do more than one job, so the useful question is which of the three a compromised barrier is short of.
The barrier is the outermost layer of skin (the stratum corneum), where flattened dead cells sit in a mortar of lipid. That lipid is roughly equal parts ceramides, cholesterol, and free fatty acids, arranged in stacked sheets between the cells [2]. A compromised barrier is a stratum corneum with too little of that lipid. In eczema-prone skin the ceramides are markedly reduced, both in the rash and in skin that looks normal [3]. In aged skin the shortfall runs across every lipid class rather than one: total barrier lipid was down by about 30 percent in aged animals. In people, researchers disrupt the barrier by pressing adhesive tape onto the skin and pulling it away, taking a layer of surface cells each time, and aged skin gave way after 18 pulls where young skin took 31. It then recovered only 15 percent of its barrier in 24 hours where young skin recovered 50 percent [4]. Either way the missing material is lipid, and the barrier repairs itself by making more.
What occlusion does, and how much of it a barrier can use
An occlusive lowers water loss in proportion to how completely it covers the skin, but a completely closed film is the wrong target because water leaving the skin is also the signal that starts repair. In animal studies, a barrier stripped with solvent rebuilt its lipids within 48 hours when left uncovered, but under a film that let no water through, lipid production never rose, no new lipid was laid down, and the barrier did not recover normally. Under a film that let water vapor through, recovery was normal, which points to the water movement itself as the signal [5]. A seal that stops all water loss also stops the process that ends the need for it.
Partial occlusion is something a compromised barrier can use though, and this comes from lipid. Occlusive materials work by spreading into the lipid between the surface cells and adding to it [1], which is the same place an emollient works. On a barrier that is short of lipid, the most useful occlusive is the lipid that replaces what is missing, and it slows water loss simply by being there. At that point the two classes stop being separate.
What emollients do, and which ones rebuild
An emollient fills the gaps between the surface cells with lipid, which is why skin feels smoother the moment an emollient goes on [1]. Whether it also rebuilds the barrier depends on which lipid the emollient is made of.
In animal studies, a lipid that is not part of the barrier's own chemistry stayed in the stratum corneum and repaired the barrier quickly by filling the gaps. The barrier's own lipids, ceramides, cholesterol, and free fatty acids, behaved differently. They passed through the stratum corneum into the living cells beneath, which packaged them into the small parcels the cells use to ship new lipid up into the barrier, and the recovery that followed was slower but structural, with normal parcels and a normally built lipid layer [6]. Filling is quick, while rebuilding takes longer and leaves the barrier better off than it was before.
The mixture has to be complete. In animal studies, ceramide on its own, fatty acid on its own, and every two-lipid pairing delayed recovery and produced faulty lipid parcels, while all three together allowed normal recovery [7]. Which of the three should lead depends on what the skin is missing. In aged skin, a mixture led by cholesterol sped up recovery, in a small human study at 6 hours, and in aged animals a mixture led by fatty acids slowed it [8]. In a small clinical study of children with eczema, a cream led by ceramides lowered water loss and restored the barrier's lipid structure [9]. A barrier short on ceramides wants ceramides, and a barrier short on everything wants cholesterol first.
The skin's own surface oils belong in this class too. Squalene and wax esters are found in human sebum and nowhere else in the body [10], squalane is the stable, saturated form of squalene that doesn't oxidize [11], and jojoba wax is the main plant source of wax esters related to the esters naturally found in sebum [12]. An emollient built from these and from the barrier's structural lipids supplies material the skin already recognizes, in the place the shortfall is.
What humectants do, and when they work against the barrier
A humectant pulls water toward the stratum corneum. Glycerin is the most effective of them [1], and its work in skin goes beyond holding water: it keeps the barrier's lipids from stiffening, helps the surface cells let go when they are due to shed, and improves barrier function and suppleness in dry skin [13]. Urea and lactic acid attract water the same way [1], and so does hyaluronic acid, a molecule that binds water and holds it in the skin [14].
The caveat is in the direction of the pull. A humectant draws water up from the living skin toward the surface, where it evaporates, so on its own a humectant increases transepidermal water loss, the water that escapes through the skin. That is why formulators pair humectants with an occlusive [1]. On a barrier that is already leaking, a humectant with nothing over it moves water toward the surface and out. Under a lipid, the same humectant hydrates the stratum corneum and stays. Order settles the rest. A water-based humectant product goes on first and a lipid product goes on last, because a lipid applied over a product can double how much of it penetrates, while a lipid applied first reduces what follows [15].
The three classes in one place
| Occlusive | Emollient | Humectant | |
|---|---|---|---|
| How it works | Water-repellent film that blocks evaporation [1] | Lipid that fills between the surface cells. The barrier's own lipids are rebuilt into new structure [1, 6] | Attracts water and pulls it into the stratum corneum [1] |
| Examples | Petrolatum, lanolin, mineral oil, silicones [1] | Squalane, jojoba esters, ceramides, cholesterol, fatty acids, plant oils [1, 10, 12] | Glycerin, urea, lactic acid, hyaluronic acid [1, 13, 14] |
| Effect on water loss | Lowers it in proportion to how closed the film is [1] | Lowers it by filling the lipid gaps [1] | Raises it unless a lipid covers it [1] |
| Effect on repair | Partial cover leaves the repair signal intact. A closed film stalls it [5] | A complete mix of the barrier's own lipids allows or speeds it. An incomplete mix delays it [7, 8] | Glycerin supports it. A humectant alone does not rebuild lipid [13] |
| What a compromised barrier needs from it | Enough to slow loss, not enough to stop it | The lipid classes it is short on, all of them | Only under a lipid |
How Māteriā applies this
Omnia is an anhydrous solid serum, so its emollients and its occlusives are the same materials: a lipid base of squalane, jojoba esters, and fast-spreading plant-derived esters, with ceramide NP, a phytosterol lipid that forms the barrier's stacked-sheet structure, and oat kernel oil carried within it. There is no humectant. The formula supplies lipid and slows water loss. A water-based humectant product layers under it, where the lipid holds the water it draws in. The full ingredient list and the role of each material are on the Omnia page. The reasoning behind the barrier-first approach is on The Science of Biomimetic Design.
Sources
- Sethi A, Kaur T, Malhotra SK, Gambhir ML. Moisturizers: the slippery road. Indian Journal of Dermatology. 2016;61(3):279–287. https://pmc.ncbi.nlm.nih.gov/articles/PMC4885180/
- van Smeden J, Janssens M, Gooris GS, Bouwstra JA. The important role of stratum corneum lipids for the cutaneous barrier function. Biochimica et Biophysica Acta. 2014;1841(3):295–313. https://www.sciencedirect.com/science/article/abs/pii/S1388198113002485
- Imokawa G, Abe A, Jin K, Higaki Y, Kawashima M, Hidano A. Decreased level of ceramides in stratum corneum of atopic dermatitis: an etiologic factor in atopic dry skin? Journal of Investigative Dermatology. 1991;96(4):523–526. https://pubmed.ncbi.nlm.nih.gov/2007790/
- Ghadially R, Brown BE, Sequeira-Martin SM, Feingold KR, Elias PM. The aged epidermal permeability barrier: structural, functional, and lipid biochemical abnormalities in humans and a senescent murine model. Journal of Clinical Investigation. 1995;95(5):2281–2290. https://pmc.ncbi.nlm.nih.gov/articles/PMC295841/
- Grubauer G, Elias PM, Feingold KR. Transepidermal water loss: the signal for recovery of barrier structure and function. Journal of Lipid Research. 1989;30(3):323–333. https://pubmed.ncbi.nlm.nih.gov/2723540/
- Mao-Qiang M, Brown BE, Wu-Pong S, Feingold KR, Elias PM. Exogenous nonphysiologic vs physiologic lipids: divergent mechanisms for correction of permeability barrier dysfunction. Archives of Dermatology. 1995;131(7):809–816. https://pubmed.ncbi.nlm.nih.gov/7611797/
- Man MQ, Feingold KR, Elias PM. Exogenous lipids influence permeability barrier recovery in acetone-treated murine skin. Archives of Dermatology. 1993;129(6):728–738. https://pubmed.ncbi.nlm.nih.gov/8507075/
- 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;37(3):403–408. https://pubmed.ncbi.nlm.nih.gov/9308554/
- Chamlin SL, Kao J, Frieden IJ, et al. Ceramide-dominant barrier repair lipids alleviate childhood atopic dermatitis. Journal of the American Academy of Dermatology. 2002;47(2):198–208. https://pubmed.ncbi.nlm.nih.gov/12140465/
- Picardo M, Ottaviani M, Camera E, Mastrofrancesco A. Sebaceous gland lipids. Dermato-Endocrinology. 2009;1(2):68–71. https://pubmed.ncbi.nlm.nih.gov/20224686/
- Huang ZR, Lin YK, Fang JY. Biological and pharmacological activities of squalene and related compounds. Molecules. 2009;14(1):540–554. https://www.mdpi.com/1420-3049/14/1/540
- Gad HA, Roberts A, Hamzi SH, et al. Jojoba oil: an updated comprehensive review on chemistry, pharmaceutical uses, and toxicity. Polymers. 2021;13(11):1711. https://pubmed.ncbi.nlm.nih.gov/34073772/
- Fluhr JW, Darlenski R, Surber C. Glycerol and the skin: holistic approach to its origin and functions. British Journal of Dermatology. 2008;159(1):23–34. https://pubmed.ncbi.nlm.nih.gov/18510666/
- Papakonstantinou E, Roth M, Karakiulakis G. Hyaluronic acid: a key molecule in skin aging. Dermato-Endocrinology. 2012;4(3):253–258. https://pubmed.ncbi.nlm.nih.gov/23467280/
- Burstein SE, Maibach HI. Sequential topical application and percutaneous penetration: a systematic review. Skin Pharmacology and Physiology. 2026;39(2):84–98. https://karger.com/spp/article/39/2/84/943839
