| Exfoliation types | Chemical (AHAs, BHAs) and physical (scrubs) |
| Skin barrier pH range | Approximately 4.5–5.5 (Dermatology literature, general consensus) |
| Retinol vs. Tretinoin | Retinol: OTC; Tretinoin: prescription-strength |
| Label order rule | Ingredients listed highest to lowest concentration (FDA cosmetics labeling regulations) |
| Hyaluronic acid capacity | Can hold up to 1,000x its weight in water (Widely cited in cosmetic chemistry literature) |
| Niacinamide concentration range | 2–10% in most OTC formulations |
Why Ingredient Literacy Matters
Skincare products routinely list a dozen or more ingredients — often in scientific Latin under the INCI naming system — and marketing language rarely clarifies what those ingredients actually do. Understanding the vocabulary helps you evaluate whether a product is formulated for your skin's needs, identify potential irritants, and cut through the noise of trend-driven claims.
This glossary covers the categories and terms you'll encounter most frequently on labels, organized by function. It is a general educational reference, not personalized skincare advice. If you have a skin condition or are considering a prescription-strength treatment, consult a board-certified dermatologist.
| Exfoliation types | Chemical (AHAs, BHAs) and physical (scrubs) |
| Skin barrier pH range | Approximately 4.5–5.5 (Dermatology literature, general consensus) |
| Retinol vs. Tretinoin | Retinol: OTC; Tretinoin: prescription-strength |
| Label order rule | Ingredients listed highest to lowest concentration (FDA cosmetics labeling regulations) |
| Hyaluronic acid capacity | Can hold up to 1,000x its weight in water (Widely cited in cosmetic chemistry literature) |
| Niacinamide concentration range | 2–10% in most OTC formulations |
Exfoliants: AHAs, BHAs, and PHAs
Chemical exfoliants dissolve the bonds holding dead skin cells together rather than physically scrubbing them away. The three main categories differ primarily in solubility and how deeply they act.
- AHAs (glycolic, lactic, mandelic acid) are water-soluble and work primarily at the surface. Glycolic acid has the smallest molecular size and penetrates readily; lactic acid is gentler and also functions as a humectant.
- BHAs (most commonly salicylic acid) are oil-soluble, allowing them to work within pores. This makes them particularly relevant for congested or acne-prone skin.
- PHAs (polyhydroxy acids, such as gluconolactone) are a newer category with a larger molecular size, resulting in slower penetration and generally lower irritation potential — often recommended for sensitive skin types.
Concentration and pH are critical to how effectively these acids work. Products with an active exfoliant but a high pH may provide less benefit than the label implies. For a detailed look at how label order signals concentration, see our label-reading guide.
Moisturizing Ingredients: The Three Functional Types
Effective moisturization typically relies on a combination of three ingredient categories working together rather than any single "super-ingredient."
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Moisturizer ingredient categories
Dermatologists broadly classify moisturizing ingredients into three functional types: humectants, emollients, and occlusives.
~4.5–5.5
Optimal skin surface pH
Maintaining this mildly acidic range supports barrier function and microbial balance, according to peer-reviewed dermatology research.
- Humectants
- Draw water toward the skin. Hyaluronic acid is the most marketed humectant, valued for its water-retention capacity. Glycerin and urea are equally functional and often more cost-effective in formulations. Urea at higher concentrations also acts as a mild exfoliant.
- Emollients
- Soften skin texture by filling intercellular spaces. Plant-derived oils (jojoba, squalane, rosehip), shea butter, and fatty acids like linoleic acid all serve emollient functions. The right choice depends on skin type — lighter oils suit oily skin; richer emollients suit dry or mature skin.
- Occlusives
- Seal moisture in. Petrolatum is considered the gold standard for occlusion; beeswax, lanolin, and silicones like dimethicone also function this way. Occlusives are most effective applied over a humectant layer, trapping the moisture that has already been drawn to the surface.
Ceramides sit at the intersection of these categories — they are lipids that reinforce the skin barrier structurally, reducing ongoing water loss rather than actively supplying or retaining water.
Ingredient Labels Follow Regulated Rules
In the United States, the FDA requires cosmetic ingredient lists to follow INCI naming conventions and to list ingredients in descending order of concentration. Ingredients present at 1% or below may be listed in any order after those above 1%. See our guide to reading skincare labels for a deeper breakdown of how this works in practice.
Actives: Retinoids, Vitamin C, Niacinamide, and Peptides
"Actives" is an informal term for ingredients with a specific, targeted mechanism of action supported by research — as opposed to base or functional ingredients like emulsifiers and preservatives.
Retinoids
Vitamin A derivatives that influence cell turnover. Over-the-counter retinol must be converted by the skin into its active form (retinoic acid), making it milder but slower-acting than prescription tretinoin. Adapalene, once prescription-only, is now available OTC at 0.1% for acne. All retinoids can cause dryness and sensitivity during an adjustment period and increase photosensitivity — daily sunscreen is considered essential when using them. For more on sunscreen labeling, see our SPF explainer.
Vitamin C
L-ascorbic acid is the most studied form, functioning as an antioxidant and supporting collagen synthesis. It is inherently unstable and degrades with light and air exposure — packaging and formulation pH (below 3.5) matter significantly. Derivative forms such as ascorbyl glucoside are more stable but require conversion in the skin and may be less potent.
Niacinamide
A versatile, well-tolerated ingredient with research supporting its effects on uneven tone, pore appearance, and barrier reinforcement. It works across a broad pH range and pairs well with most other ingredients, making it a practical multi-benefit active.
Peptides
Amino acid chains with signaling roles in the skin. While the category is broad and ingredient-specific evidence varies, certain peptides — such as palmitoyl pentapeptide-4 — have been studied for their role in supporting collagen production. Claims around peptides differ widely between products; scrutinize the research basis rather than marketing language.
This article is for general informational and educational purposes only and does not constitute medical or dermatological advice. Consult a qualified healthcare professional for guidance specific to your skin type or condition.