How skincare ingredients work usually comes down to one of a handful of jobs: drawing in water, sealing it in, smoothing texture, loosening dead cells, or shielding skin from the sun.
Once you know which job an ingredient is doing, a product label stops feeling like a chemistry quiz. Here is a plain-language look at how skincare ingredients work, organized by category, with notes on what dermatology research actually says about each one.
Key Takeaways
- Humectants like glycerin and hyaluronic acid work by drawing and binding water into the skin's outer layer.
- Occlusives like petrolatum and dimethicone work differently — they form a surface layer that slows water loss rather than adding water.
- Urea and lactic acid can do double duty: raising skin's water-holding capacity while also loosening bonds between surface cells, which is why they double as mild exfoliants.
- Mineral sunscreen ingredients sit on top of skin and reflect or scatter UV rays, while chemical sunscreen ingredients absorb UV and convert it to heat.
- Knowing what category an ingredient falls into often explains more about how a product will feel and perform than its marketing name does.
Humectants: Ingredients That Draw in Water
Humectants are the ingredients responsible for pulling water into the skin's outer layer and helping it stay there. Glycerin is considered especially valuable, because beyond simply attracting moisture, it's also thought to help modulate aquaporins — the water channels that help skin move moisture where it's needed, according to Dermatology Times. Other common humectants include hyaluronic acid, sodium hyaluronate, and sodium PCA, each of which binds water molecules to itself.
Urea and lactic acid play a dual role worth knowing about. Both may help raise skin's water-holding capacity by opening water-binding sites on proteins — a humectant-like effect — while also loosening the bonds between cells in the skin's outer layer. That is why the same ingredient can show up in a hydrating formula and an exfoliating one. For a closer look at ingredient-by-ingredient function, our skincare ingredients glossary breaks these down individually.
Occlusives and Emollients: Ingredients That Seal It In
Occlusives work through an entirely different mechanism. Rather than adding water, they form a surface layer that slows transepidermal water loss — the ongoing process of water escaping through skin into the surrounding air. Petrolatum, mineral oil, and silicone derivatives like dimethicone and cyclomethicone are common occlusives, along with certain polymers. Plant-based alternatives such as cocoa butter, shea butter, hemp oil, and sesame seed oil are popular in naturally formulated products, though they tend to be less effective at slowing water loss than petrolatum or mineral oil.
Emollients do yet another job: they smooth and soften skin by filling in small gaps between skin cells, which can improve how a product feels and how skin looks in the short term — a different mechanism from a humectant adding water or an occlusive sealing it in. That's part of why a well-formulated moisturizer often leans on all three. If you're comparing textures, a lotion, gel, or balm will usually combine humectant, occlusive, and emollient ingredients in a different balance.
How Skincare Ingredients Work: Exfoliants, Antioxidants, and Sunscreen
Not every ingredient is about moisture. Exfoliants such as urea and lactic acid, mentioned above, loosen the bonds between cells on the skin's surface, which may help dead cells shed more evenly. Antioxidants like vitamin C and vitamin E are generally understood to help limit some of the free-radical damage linked to UV and environmental exposure, though they're best thought of as a supporting ingredient rather than a stand-alone defense.
Sunscreen ingredients split into two mechanisms. Mineral (physical) filters like zinc oxide and titanium dioxide sit on top of skin and reflect or scatter UV rays, while chemical filters like avobenzone and octocrylene absorb UV radiation and convert it into heat that's released from the skin. Both types are considered effective when applied generously and reapplied as directed. If you're building a routine around oilier skin, pair these ingredient categories with the non-comedogenic choices that suit combination skin, and see our companion piece on skin pH and your skin barrier for how acidity affects the way these ingredients perform.
How Skincare Ingredients Work FAQ
What's the difference between a humectant and an occlusive?
A humectant, like glycerin or hyaluronic acid, draws and binds water into the skin's outer layer. An occlusive, like petrolatum or dimethicone, works differently — it forms a surface layer that slows water loss rather than adding water itself. Many moisturizers combine both.
Why do some ingredients act as both a moisturizer and an exfoliant?
Urea and lactic acid can raise skin's water-holding capacity by opening water-binding sites on proteins, while also loosening the bonds between cells on the skin's surface — which is why they show up in both hydrating and exfoliating formulas.
How is mineral sunscreen different from chemical sunscreen?
Mineral sunscreen ingredients like zinc oxide and titanium dioxide sit on top of the skin and reflect or scatter UV rays. Chemical sunscreen ingredients absorb UV radiation and convert it to heat that's released from the skin. Both are considered effective when used correctly and reapplied.