TL;DR: The standard moisturizer pyramid teaches three ingredient classes as if they were rungs of a ladder. They are not a ladder. They are a climate-dependent prescription. I have used the same dry skin in Karachi, London, and Toronto, and the right ratio of humectant to emollient to occlusive flipped twice in those three cities. The Loden and Bouwstra papers tell you why.
A reader in Calgary sent me a question last December about why her favourite Korean moisturizer, which had worked beautifully in Vancouver, was failing her now that she had moved inland. The product was a lightweight hyaluronic gel from a brand she had used for three years. Her face had started peeling in November and was actively cracking by January. The product had not changed. The skin had not changed. The air had changed, and the moisturizer was no longer the right tool for it.
This is the most common conversation I have with dry-skinned readers. The moisturizer they bought in summer is the wrong moisturizer for winter. The moisturizer they bought in a humid coastal city is the wrong moisturizer for a continental winter at minus fifteen. The standard skincare advice treats moisturizer choice as a function of skin type. It is closer to a function of skin type multiplied by ambient humidity.
What the studies actually show
Loden 2003 (PMID: 14572299) is the foundational review for how topical emollients work. The paper divides the active ingredients in moisturizers into three functional classes. Humectants attract water. Emollients fill the spaces between corneocytes and smooth the surface. Occlusives form a film that slows transepidermal water loss. Loden makes the point, which is often skipped in the consumer-facing version of this framework, that the three classes are not interchangeable and that the appropriate ratio depends on the environment the skin is sitting in.
Bouwstra and Ponec 2006 (PMID: 16945325) describes the stratum corneum lipid architecture that the emollients are interacting with. The intercellular lipid matrix is composed of ceramides, cholesterol, and free fatty acids in roughly equimolar ratios, organised into lamellar bilayers between corneocytes. The barrier function depends on the integrity of this organisation. Dry skin, in the clinical sense, is skin where this organisation is compromised. The compromise can be genetic, inflammatory, or environmentally induced. The intervention has to match the source.
Rawlings and Harding 2004 (PMID: 14728698) details the natural moisturizing factor (NMF), the hygroscopic mixture of amino acids, urea, lactate, and pyrrolidone carboxylic acid that sits inside the corneocytes and binds water. NMF concentration drops in low-humidity environments, partly because the precursor protein filaggrin is converted to NMF in response to ambient water gradient. This is the mechanism by which dry air actually dries skin. The corneocytes have less water to bind and the barrier loses its hydrostatic structure.
The three classes and what they actually do
Humectants pull water from the environment into the stratum corneum. Glycerin is the most studied and most used. Hyaluronic acid, urea, panthenol, betaine, sodium PCA, and the various sugar-derived molecules in this class behave similarly with different molecular weights and binding capacities. In a humid environment, humectants pull water from the air into the skin. In a dry environment, the gradient reverses. Humectants applied to skin in a low-humidity room will pull water out of the deeper epidermis to the surface, where it evaporates. This is the failure mode the Calgary reader was experiencing. Her hyaluronic gel was actively dehydrating her face.
Emollients fill gaps between corneocytes and improve the cosmetic surface of the skin. Squalane, jojoba ester, isopropyl palmitate, cetyl alcohol, dimethicone, and the various plant-derived oils in this class do not, in themselves, prevent water loss. They smooth the skin and improve flexibility. They feel pleasant. Most of the moisturizing sensation a user experiences in the first ten minutes of application is emollient effect.
Occlusives form a hydrophobic film over the skin surface that slows the rate at which water evaporates from the stratum corneum. Petrolatum is the gold standard. Mineral oil is close behind. Beeswax, lanolin, dimethicone at high concentrations, and shea butter all behave occlusively to varying degrees. Petrolatum reduces TEWL by roughly 99% in the controlled measurements summarised by Sethi et al. 2016 (PMID: 27293248). Nothing else comes close.
The hierarchy taught in most skincare content is humectant, then emollient, then occlusive, layered in that order. This is correct in terms of layering sequence. It is wrong as a general prescription. The question is not which order to apply them. The question is what ratio of each is appropriate for the climate.
Climate as the dominant variable
In a humid environment, humectants do most of the work. The air provides the water source. Glycerin and hyaluronic acid pull moisture in. The barrier holds it. Emollient smoothing is a nice-to-have. Occlusion is largely unnecessary and can feel suffocating. This is the climate the Korean and Japanese moisturizer formulations are designed for. Tokyo summer humidity sits at 70 to 80%. Seoul is similar. The light gel-cream textures that dominate those markets work because the ambient humidity is doing half the job.
In a dry environment, the situation inverts. Humectants without occlusion are net-negative. They pull water from deeper skin to the surface, where it evaporates into the air. The skin loses water faster than it would have without the product. The Verdier-Sévrain and Bonté 2007 review (PMID: 17524122) describes this gradient reversal in detail. The fix is to apply the humectant under an occlusive, so the water that gets pulled to the surface is trapped there.
The threshold appears to sit around 45 to 50% ambient humidity. Above that, light textures and humectant-heavy formulations are appropriate. Below that, the occlusive component becomes load-bearing. Winter indoor heating in a continental climate often produces ambient humidity in the 20 to 30% range, which is similar to a desert and worse for skin than most outdoor winter air.
What the right product looks like by climate
For humid coastal climates above 60% humidity: lightweight gel-cream textures with glycerin, hyaluronic acid, sodium PCA, and a small amount of emollient. Beauty of Joseon Dynasty Cream is a clean example. La Roche-Posay Toleriane Sensitive Fluid works in this range. The occlusive component is minimal and the formulation feels weightless.
For temperate climates between 45 and 60% humidity: balanced formulations with all three classes present. CeraVe Moisturising Cream is the canonical example. Glycerin and hyaluronic acid for humectant load, ceramides and fatty acids for barrier repair, petrolatum for occlusive slowdown. Cetaphil Moisturising Cream is functionally similar.
For dry climates below 45% humidity, including most heated indoor environments in winter: heavier formulations with significant occlusive presence. CeraVe Healing Ointment, La Roche-Posay Cicaplast Baume B5, Aquaphor, and pure petrolatum (Vaseline) all sit at the heavy end. The “slugging” technique, applying a thin layer of petrolatum over a humectant serum, is a manual version of the same logic for people who do not want to commit to a heavy formulation full-time.
What I changed in three cities
In Karachi summer, ambient humidity around 65%, I used a glycerin and squalane gel from The Ordinary with no occlusive. The skin was fine.
In London, ambient humidity around 75% outdoor and around 40% indoor with heating in winter, I used CeraVe Moisturising Cream daily and added a small amount of petrolatum on the cheeks during the coldest weeks.
In Toronto, ambient humidity around 50% outdoor in summer and around 20% indoor in deep winter, the CeraVe was insufficient by January. I switched to the Cerave PM facial moisturizer with a layer of Aquaphor over the top three nights a week. The cracking around the nostrils that I had had in my first Toronto winter did not recur in the second.
The product change tracked the climate change, not any change in my skin.
What I would tell my past self
Buy moisturizer for the room you are in, not the skin type you have. The climate is the dominant variable for dry skin.
If you live in a humid place, do not buy heavy occlusive formulations. They will feel uncomfortable and they will not improve your barrier function. The Japanese and Korean lightweight formulations exist because their target market lives in humidity. They are not bad products. They are products for a different environment.
If you live in a dry place, or run heated indoor air in winter, the occlusive layer is not optional. A humectant serum without an occlusive over the top is worse than no serum at all on a cold dry day. The water is going somewhere. If the formulation does not include occlusion, the slugging technique with a thin layer of petrolatum at night accomplishes the same thing.
Watch the humidity in your bedroom. A $20 hygrometer is more useful for a dry skin routine than any product upgrade. If the reading is below 35%, a humidifier is doing more for your skin than any moisturizer.
Petrolatum is the most boring and most effective occlusive on the market. The Loden review specifically notes that petrolatum-based formulations consistently outperform plant-oil alternatives in TEWL reduction. The plant oils feel nicer. Petrolatum works better. For severe winter dryness, this matters.
FAQ
Why do my Korean skincare products stop working in winter?
Most Korean formulations are calibrated for high-humidity climates. The humectant load assumes the air will provide water. In dry winter conditions, the humectants pull water from deeper skin and the formulation runs against you.
Is hyaluronic acid bad for dry skin in winter?
Hyaluronic acid is not bad. Hyaluronic acid applied to dry skin in a dry room without an occlusive over the top is bad. The molecule needs ambient or applied water to function. Apply it to damp skin and layer an occlusive on top.
What is the cheapest effective heavy moisturizer for winter?
A 200 g tub of Vaseline Original costs around $5 in most markets. Applied as a thin layer over a basic humectant moisturizer at night, it is the most cost-effective barrier protection on the market. The cosmetic experience is greasy. The barrier outcome is excellent.
Do face oils count as moisturizers?
Most face oils function as emollients, not as full moisturizers. They have no humectant load and limited occlusive effect compared to petrolatum. They smooth and they feel nice. They do not, in themselves, hydrate. Use them over a humectant layer, not in place of one.
Should I use a different moisturizer in summer and winter?
Yes, if your seasons have meaningful humidity differences. Two products, one for warm humid months and one for cold dry months, will outperform a single year-round product for most dry-skinned people in a four-season climate.
Related Elelaf tools
Sources
- Lodén M. Role of topical emollients and moisturizers in the treatment of dry skin barrier disorders. Am J Clin Dermatol. 2003;4(11):771-788. PMID: 14572299
- Bouwstra JA, Ponec M. The skin barrier in healthy and diseased state. Biochim Biophys Acta. 2006;1758(12):2080-2095. PMID: 16945325
- Rawlings AV, Harding CR. Moisturization and skin barrier function. Dermatol Ther. 2004;17 Suppl 1:43-48. PMID: 14728698
- Sethi A, Kaur T, Malhotra SK, Gambhir ML. Moisturizers: the slippery road. Indian J Dermatol. 2016;61(3):279-287. PMID: 27293248
- Verdier-Sévrain S, Bonté F. Skin hydration: a review on its molecular mechanisms. J Cosmet Dermatol. 2007;6(2):75-82. PMID: 17524122