Ingredient guide

A naturally occurring copper-binding tripeptide (glycyl-histidyl-lysine bound to copper) that occurs in human plasma and is widely used in topical formulas, studied for its role in the appearance of skin firmness and texture. It was first isolated from human plasma in the 1970s and has since become one of the more established peptide actives in the anti-aging category. Because copper itself is the active handle, the same property that makes it a useful signal peptide also makes it a stability concern around other reactive actives.

A pair of palmitoyl "matrikine" messenger peptides formulated together under the trademarked name Matrixyl 3000. It is the current-generation successor to the original single-peptide Matrixyl, studied for the appearance of fine lines. The blend pairs a peptide fragment associated with collagen-related signaling with a second fragment studied for easing the visible look of stressed, aged-looking skin, and it now shows up in everything from drugstore anti-aging creams to prestige multi-peptide serums.

A peptide marketed as a topical option studied for the appearance of expression lines, sometimes called a "topical alternative" in marketing copy that draws a comparison to injectable neuromodulators. It is modeled on a fragment of the SNAP-25 protein involved in the signaling pathway tied to muscle contraction, and the idea behind it is to soften the look of repeated-movement lines such as crow’s feet and forehead creases. It is one of the older "expression line" peptides on the market and remains common in drugstore and mid-range serums positioned around that claim.

The most-studied form of topical vitamin C, an antioxidant associated with the appearance of brightness and evenness and a cofactor in the skin’s own collagen-production process. It is also notoriously unstable, oxidizing on exposure to air, light and heat, so packaging and pH matter as much as the percentage on the label. Research on L-ascorbic acid dates back decades, most notably the low-pH, high-concentration formulas developed in academic research, which set the template most modern vitamin C serums still follow.

A complex of signaling proteins secreted by cultured human skin cells, the hero ingredient of prestige "growth-factor" serums, studied for the appearance of firmness and fine lines. The conditioned media is collected from fibroblasts (the cells that produce collagen and elastin) grown in culture, then formulated as a cocktail of proteins and peptides rather than a single isolated active. It sits at the higher end of the market, and because it is a proprietary, multi-protein extract, the exact composition and dose are rarely disclosed on the label.

A synthetic tripeptide included in some prestige serums and studied, in early research, for its association with the appearance of firmness. It is a smaller, more recently developed entry in the signal-peptide category, formulated at low percentages alongside other peptides rather than used as a standalone active. Public research on it is thinner than on longer-established peptides like copper peptides or Matrixyl, so most of what is documented comes from ingredient-supplier literature rather than independent clinical trials.

A palmitoylated conditioning peptide commonly paired with Matrixyl in multi-peptide serums, studied for the appearance of smoother, firmer skin. It is sold under the trade name Biopeptide CL and is generally positioned as a companion active rather than a headline ingredient, showing up alongside other palmitoyl peptides in layered anti-aging formulas. Like other palmitoylated peptides, the fatty-acid tail is meant to help it move into the upper skin layers, where it is studied for supporting the look of a more resilient surface.

The best-studied over-the-counter vitamin A derivative and the reference cosmetic retinoid, associated with the appearance of fine lines and a smoother, more even-looking surface. It has decades of published research behind it, more than almost any other cosmetic active, and remains the benchmark that newer retinoid formats are compared against. It is notoriously unstable in air and light, and it needs a gradual introduction, since the visible flaking and sensitivity many people experience early on (often called "retinization") is well documented and expected rather than a sign something has gone wrong.

Retinol wrapped in a protective carrier (liposomes, silica or polymer shells) so it stays stable longer and releases gradually, which research links to comparable appearance benefits with less of the visible irritation. It is the same active ingredient as standard retinol, just delivered differently, so it is a formulation upgrade rather than a separate class of retinoid. Encapsulation technology has become more common as brands look to make retinol more approachable for sensitive or first-time users without lowering the underlying dose.

A stable, water-soluble form of vitamin B3 and one of the more reliable multitaskers on a label, studied for the appearance of an even tone, refined-looking pores and a supported-looking barrier. It is well tolerated across most skin types, does not need special packaging, and is one of the few actives commonly recommended for both morning and evening routines. Because it is inexpensive to formulate and pairs easily with most other ingredients, it shows up across a very wide range of products, from dedicated brightening serums to moisturizers and toners where it plays a supporting role.

The zinc salt of a natural moisturising-factor amino acid (PCA, pyrrolidone carboxylic acid), usually formulated as a supporting act to niacinamide rather than a stand-alone treatment. It is included for the look of a balanced, less-shiny complexion and the appearance of a more refined surface where visible oil buildup is a concern. Because it works at low percentages and mostly appears alongside other sebum-focused actives, it reads as a finishing touch rather than the ingredient a serum is built around.

A lipophilic (fat-soluble) antioxidant and the classic partner to vitamin C, most often listed as tocopherol or tocopheryl acetate. The two are studied together, each helping regenerate the other, which is why "vitamin C plus E" formulas are far more common than either used alone. On its own it is flagged for antioxidant support and the appearance of conditioned, comfortable-looking skin, and its fat-soluble nature also lets it help stabilise oils and other actives in a formula.

A plant-derived antioxidant, a phenolic compound found in plant cell walls, best known as the stabiliser in "CE ferulic" serums. It props up vitamins C and E, extending how long that combined antioxidant activity holds up, and contributes its own antioxidant support on top of the two more famous actives. It is usually dosed below 1% by design, since its studied role is to reinforce the trio rather than to headline on its own.

A humectant that holds many times its weight in water, used at a range of molecular weights (often blended as "multi-weight HA") for the appearance of plumper, more hydrated-looking skin. Higher-weight forms sit on the surface for an immediate smoothing look, while lower-weight forms are studied for reaching a little deeper. It is a comfort and finish ingredient, not an anti-aging active, and its visible effect is tied closely to how consistently it is used.

A dicarboxylic acid found naturally in grains such as wheat, rye and barley, used in cosmetic-strength formulas for the appearance of a clearer, more even-looking complexion. It is well tolerated relative to many other acids and is often reached for by people who find retinoids or stronger exfoliants too reactive on their skin. The higher-strength versions used for certain skin conditions are prescription drugs rather than cosmetics, so cosmetic azelaic acid is a distinctly different, gentler product.

A plant compound extracted from Psoralea corylifolia seeds, marketed as a gentler "retinol alternative" for the appearance of fine lines. It is more shelf-stable than retinol and does not carry the same light-sensitivity or irritation profile, making it easier to formulate and to layer with other actives. Its evidence base is far younger and thinner than retinol’s, resting on a small number of studies rather than decades of research.

A stabilised, plant-derived brightening ingredient, a synthetic analogue of the arbutin found in bearberry, studied for the appearance of a more even tone and the look of reduced dark spots. It is typically used around 1 to 2%, a range chosen because higher percentages have not reliably shown extra visible benefit in supporting research. It is considered one of the gentler brightening options and is often paired with other tone-focused actives rather than used alone.

An oil-soluble, more shelf-stable vitamin C ester used as a gentler alternative to L-ascorbic acid, flagged for antioxidant support and the appearance of brightness. Because it does not require the very low pH that L-ascorbic acid does, it is easier to formulate into oils, creams and lotions rather than only thin, acidic serums. Derivatives like this one carry thinner direct evidence than pure vitamin C, though what exists points in a similar visible direction.

A copper-free palmitoyl "matrikine" messenger peptide, often stacked with Matrixyl 3000 in multi-peptide serums, studied for the appearance of smoother, firmer-looking skin. It was developed as a manufacturer alternative to older single-peptide signal actives, designed to complement rather than replace them. Because it does not involve copper, it avoids the layering caution that copper peptides carry with direct vitamin C.

The retinoid one conversion step closer to retinoic acid than retinol, so it works at a lower percentage while aiming for a similar visible effect. It is studied for the appearance of fine lines and an even tone, and like retinol it oxidises fast in air and light, so opaque, airless packaging matters for whether it still performs by the time a bottle is half used. It sits between retinol and prescription retinoids in the conversion chain, part of why some people find it faster-acting but also a little more assertive at first.

A synthetic amino-acid derivative studied for the appearance of stubborn discoloration and a more even tone, often paired with niacinamide or acids because it works by a different route. It is formulated topically at low leave-on percentages and has become a common pick for people looking for a gentler alternative to harsher brighteners. Because its proposed pathway does not target the pigment-making enzyme directly, it is frequently layered with tyrosinase-inhibiting actives like alpha arbutin or vitamin C rather than relied on alone.

Tiny vesicles that carry signalling cargo, proteins, lipids and RNA fragments, between cells, the newest headline in prestige serums. Depending on the brand they may be sourced from plants, platelets or lab-cultured stem-cell conditioned media, and sourcing is not yet standardized across the category. The marketing is well ahead of the cosmetic evidence, which is early and mostly brand-led, and there is no agreed-upon topical use level or vesicle count that defines an effective serum.

Provitamin B5, a humectant and skin conditioner used for the appearance of comfortable, hydrated, less-stressed-looking skin. It is a support ingredient, not an anti-aging active, and shows up across nearly every category of skincare, from serums to lip balms to after-sun care. It is generally considered one of the gentlest actives in a routine, which is why it is so often used to round out formulas built around stronger exfoliants or retinoids.

The lipids that make up much of the skin’s outer barrier, added to serums for the appearance of a comfortable, resilient-looking barrier and less visible dryness. Ceramides make up roughly half of the lipid matrix that holds surface skin cells together, and formulas are studied to work best when they mirror that natural ratio alongside cholesterol and fatty acids rather than using ceramides alone. They show up heavily in barrier-repair moisturizers and are a common way to offset the look of dryness that comes with retinoids or acids.

An oil-soluble exfoliating acid that can get inside the pore lining, studied for the appearance of clearer, more refined-looking pores and a smoother surface. It comes from the same salicylate family as willow bark and has decades of use behind it, most often in leave-on toners, spot treatments and serums built for oily or blemish-prone skin. Because it dissolves in oil rather than water, it reaches inside a congested pore in a way most other acids cannot, which is why it remains a first choice for visibly clogged pores and surface bumps.

The smallest alpha hydroxy acid and the most-studied surface exfoliant, associated with the appearance of a smoother texture, brighter even tone and softened fine lines. Its small molecular size lets it move into the surface layers of skin efficiently, which is part of why it has the deepest clinical record of any AHA and shows up across toners, serums and in-office peels alike. Results are cumulative; most of the published research looks at weeks to months of regular use rather than a single application.

A milk-thistle-derived antioxidant, best known as the namesake active in oil-focused vitamin C serums, studied for helping skin look protected against visible environmental stress. It is extracted from milk thistle seed and is most often formulated alongside vitamin C and ferulic acid rather than on its own, rounding out an antioxidant blend built for daytime use under sunscreen. It is also associated in early research with the look of a clearer, more even surface on oilier skin types.

A purified active from Centella asiatica (cica), widely used in soothing and barrier-support serums for the appearance of calmer, more comfortable-looking skin. It is one of several active compounds isolated from the same plant, alongside asiaticoside and madecassic acid, and is generally the one formulators reach for when they want a gentle, broadly tolerated soothing agent. It has become a staple of the Korean skincare "cica" category, often paired with panthenol or hyaluronic acid in barrier-focused routines.

A licorice-root-derived active used for the appearance of a calmer, more even tone, often included alongside stronger brighteners as a gentle supporting ingredient. It is a salt form of glycyrrhizin, the same compound behind licorice root’s traditional use in soothing skincare, chosen for being more water-soluble and easier to formulate at meaningful levels than the raw extract. It rarely appears as a serum’s sole active; more often it rounds out a brightening or barrier formula alongside actives like niacinamide, vitamin C or alpha arbutin.

A synthetic peptide marketed as the headline active in a proprietary "trigger factor" complex, with cosmetic evidence that is early and largely limited to the brand that developed it. It rose to prominence through a single high-profile prestige serum, and independent, brand-neutral research on the ingredient outside of that formula is still sparse. As with many single-brand signal peptides, the concentration and delivery system used in that formula are proprietary, so results are not necessarily transferable to other products listing it on the label.

A palmitoylated signal peptide sold under the trade name Syn-Coll and formulated into multi-peptide anti-aging serums, studied for the appearance of firmer skin and softened fine lines. It belongs to the same matrikine family as Matrixyl, peptides designed to mimic the small fragments left behind when collagen breaks down, which is thought to prompt skin to behave as though it needs rebuilding. Its published record is thinner and more manufacturer-led than Matrixyl 3000, so it tends to appear as a supporting peptide in a blend rather than as a serum’s sole active.

A larger, milder alpha hydroxy acid than glycolic that also acts as a natural moisturising factor, studied for the appearance of a smoother, brighter surface with more hydration and less sting. It is produced by fermentation (traditionally from milk sugars, now usually plant-derived) and shows up across the concentration spectrum, from gentle daily leave-ons to stronger in-office peels. Because it exfoliates and holds water at the same time, it is often the AHA recommended first for drier or acid-sensitive skin.

The largest of the common alpha hydroxy acids, derived from bitter almonds and marketed as the gentle option for the appearance of an even tone. Its size means it penetrates more slowly than glycolic or lactic acid, part of why it is often recommended for deeper skin tones prone to visible post-blemish marks. Its evidence base is younger and thinner than glycolic or lactic, with more of the research focused on acne-prone and melasma-prone skin than on general photoaging.

A polyhydroxy acid, the gentlest of the exfoliating acid families, studied for the appearance of a smoother surface with very little sting. Its molecule is larger still than mandelic acid, so it exfoliates mostly at the very surface and is generally considered suitable for skin that reacts poorly to AHAs and BHAs. It also functions as a humectant and mild antioxidant, part of why it shows up in sensitive-skin and rosacea-adjacent lines as an entry point into exfoliation.

A compound produced by certain fungi during fermentation, used in brightening formulas for the appearance of dark spots and a more even tone. It works on the same tyrosinase pathway as several other brighteners, which is why it is rarely sold alone and is usually blended with niacinamide, tranexamic acid or alpha arbutin for a broader effect. It oxidises and browns readily in air and light, so packaging and freshness matter, and a browning serum is a visible sign that potency is fading.

A water-soluble, pH-stable phosphate salt of vitamin C used as a gentler, non-stinging alternative to L-ascorbic acid, studied for antioxidant support, the appearance of brightness, and the look of blemish-prone skin. Because it tolerates a near-neutral pH, it can be formulated alongside actives that would clash with L-ascorbic acid, which makes it a common choice in multitasking or sensitive-skin serums. Some laboratory research also points to activity against acne-related bacteria, part of why it turns up in blemish-focused formulas as often as in brightening ones.

An etherified, water-soluble vitamin C derivative that is more stable than L-ascorbic acid and converts to ascorbic acid in skin, studied for antioxidant support and the appearance of brightness and even tone. Its ether linkage protects the vitamin C from oxidising as quickly as the pure acid, letting it formulate at a wider pH range without the stinging L-ascorbic acid is known for. It is less studied on its own than L-ascorbic acid, so its case rests on being a stable, well-tolerated way to deliver vitamin C benefits rather than on a distinct mechanism.

A vitamin A ester that skin converts, by way of retinol, toward retinoic acid, used as a gentler retinoid (notably in Olay serums). It is milder than retinol and carries a lighter evidence base, with much of the supporting research funded or run by the brands that popularized it. Because it needs an extra conversion step, it is generally positioned as an easing-in retinoid for people who find retinol or retinaldehyde too irritating.

The mildest and most common vitamin A ester, several conversion steps from the active form, which makes it the weakest of the retinoids. It is stable and gentle but poorly evidenced on its own, and shows up more often as a supporting line on an INCI list than as a serum headline active. Because the effective dose that reaches skin is small, it is best treated as a mild conditioning ingredient rather than a substitute for retinol or a prescription retinoid.

A filtered secretion from snails, a K-beauty essence staple, used at high percentages for the appearance of plumper, more hydrated skin. It is a mixture of glycoproteins, hyaluronic acid, glycolic acid and other conditioners rather than a single active, and it is not vegan. Popularized by Korean skincare brands, it is now sold worldwide in essences, ampoules and creams, usually disclosed at a high percentage as a hydrating base rather than as a treatment active.

A water or ferment drawn from rice bran, the base of many K-beauty glow essences, used for the appearance of a brighter, more even-looking complexion. It carries starches, amino acids, vitamins and antioxidants rather than one headline molecule, so its effect reads as a gentle overall conditioning one rather than a single dosed active. Rice water has centuries of traditional use as a skin and hair rinse across East Asia, which is part of why it anchors so many minimalist toner and essence lines. Formulas vary widely in how the rice is processed, from a simple soaked water to a fermented filtrate, and that processing changes how much of the amino-acid and antioxidant content survives into the bottle.

The centella asiatica plant and its purified triterpenes, the cica in K-beauty soothing serums, used for the appearance of a calmer, less-reddened-looking complexion. It is one of the better-studied soothing botanicals, with research spanning whole-leaf extracts and isolated actives such as madecassoside and asiaticoside. Cica products range from light daily essences to thick, occlusive-feeling creams marketed at compromised- or reactive-looking skin, and the plant shows up across skincare, wound-care gels and traditional herbal preparations alike.

A resin bees collect from tree buds and sap, used at high percentages in glow serums for the appearance of a nourished, dewy-looking complexion. It carries flavonoid antioxidants such as galangin and pinocembrin along with waxes and resins, varies significantly by hive and region, and is not vegan. Propolis has a long history in traditional remedies, which is part of why it carries an artisanal, natural-ingredient halo in glow-serum marketing.

A yeast-ferment filtrate, the Pitera in SK-II style essences, used at very high percentages for the appearance of a brighter, smoother-looking complexion. It is a ferment blend rich in amino acids, minerals, organic acids and vitamins rather than a single active, produced by fermenting a strain of Galactomyces (a yeast related to sake brewing) and filtering out the solids. The format popularized the modern essence step in Japanese and Korean routines, applied as a watery liquid before serums.

A lab-made or plant-expressed version of epidermal growth factor, a signalling protein naturally involved in wound healing, used in prestige serums for the appearance of firmer, smoother-looking skin. It is a large, fragile molecule, so stability and delivery are open questions, and most cosmetic versions are recombinant or plant-expressed rather than derived from human or animal tissue. It tends to appear in expensive, ampoule-style products layered under the promise of cell communication and renewal-looking skin.

An East Asian plant used at high percentages in K-beauty soothing serums and toners for the appearance of a calmer, less-reddened-looking complexion. It sits alongside centella as a popular cica-style botanical, and its heart-shaped leaf is where the common name comes from. Houttuynia has a long history of use in traditional East Asian herbal preparations, and the extract is now marketed heavily toward oily, blemish-prone and reactive-looking skin types.

A postbiotic made by fermenting Bifidobacterium and breaking the culture down into a filtrate of amino acids, peptides, sugars and nucleotides. It is the hero of several prestige "repair" serums and now shows up at high percentages in K-beauty ampoules, used for the appearance of a stronger, more resilient-looking barrier and a smoother surface.

A traditional East Asian herb used at high percentages in minimalist Korean essences and toners for the appearance of calmer, less-reddened skin. It sits in the same soothing, cica-style family as centella and heartleaf, and is a favourite for reactive-looking skin.

An anthocyanin-rich extract of black (purple) rice, a darker, more pigmented fraction than the pale rice water used in glass-skin toners. It is used in K-beauty serums for the appearance of firmer, more radiant-looking skin, on the strength of its natural antioxidant content.

An extract of unripe green tangerine, a Jeju-grown citrus naturally high in vitamin C and flavonoids, used in K-beauty vita C dark-spot serums. It is a whole-fruit botanical source of vitamin C, not a purified or stabilised ascorbic acid, so it behaves gently and its evidence is thinner than a true vitamin C serum.