The guides · by ingredient
The actives, read one at a time.
eU· AI curatorAsk me which piece on the shelf carries any of these, and at what strength.
Mechanism, pH, what it pairs with, what it fights. Everything eU carries about the actives that move skin: 40 ingredients, sourced from the cosmetic-chemistry literature.
Every active
Retinol
Vitamin A alcohol that converts in-skin to retinaldehyde then retinoic acid. Accelerates cell turnover, supports the …
Read the guide →Retinal
Retinaldehyde — one enzymatic step from retinoic acid, faster-acting than retinol with a shorter irritation window. S…
Read the guide →Tretinoin
Retinoic acid — the active form vitamin A receptors bind directly. Prescription-only in most markets. Fastest-acting …
Read the guide →Retinyl Palmitate
Retinoid ester — the most stable, most gentle form in the vitamin A family. Converts via two enzymatic steps (palmita…
Read the guide →Niacinamide
Vitamin B3 — multifunctional water-soluble active that supports barrier function, visibly addresses the look of uneve…
Read the guide →Vitamin C
L-ascorbic acid — antioxidant that supports the look of brighter, more even tone. Neutralizes free radicals before UV…
Read the guide →Glycolic Acid
Alpha-hydroxy acid with the smallest molecular weight of the AHA family, allowing relatively deeper skin penetration.…
Read the guide →Lactic Acid
Alpha-hydroxy acid derived from fermentation. Larger molecule than glycolic acid — gentler exfoliation profile. Also …
Read the guide →Mandelic Acid
Alpha-hydroxy acid with the largest molecular weight of common AHAs — produces the most gradual exfoliation. Particul…
Read the guide →Gluconolactone
Polyhydroxy acid (PHA) — chemical exfoliant with a larger molecular weight than AHAs. Delivers the smoothing effect o…
Read the guide →Salicylic Acid
Beta-hydroxy acid (BHA) — oil-soluble, allowing penetration into sebum-filled pores where it dissolves the bonds betw…
Read the guide →Hyaluronic Acid
Naturally occurring humectant polysaccharide — draws and holds water in the upper layers of skin. Molecular weight de…
Read the guide →Polyglutamic Acid
High-molecular-weight polypeptide humectant — surface-level water retention. Often cited as having substantially high…
Read the guide →Sodium PCA
Sodium salt of pyrrolidone carboxylic acid — a key component of skin's natural moisturizing factor (NMF). Highly hygr…
Read the guide →Ceramides
Lipids (ceramide NP, AP, EOP, NS, and others) that form roughly 50% of the stratum corneum lipid matrix. Work synergi…
Read the guide →Squalane
Saturated hydrocarbon lipid — biomimetic (mirrors skin sebum composition). Functions as an emollient and carrier, enh…
Read the guide →Rosehip Oil
Cold-pressed oil from Rosa canina seeds — rich in linoleic acid (omega-6) and alpha-linolenic acid (omega-3). Skin pr…
Read the guide →Sea Buckthorn Oil
Oil from Hippophae rhamnoides berries — exceptionally rich in omega-7 (palmitoleic acid), carotenoids (beta-carotene,…
Read the guide →Panthenol
Provitamin B5 — converts in skin to pantothenic acid. Humectant and soothing agent. Supports skin comfort during the …
Read the guide →Centella
Botanical extract (Centella asiatica) containing asiaticoside, madecassoside, and asiatic acid. Soothing — associated…
Read the guide →Allantoin
Derived from comfrey root (or synthetic). Soothing and mildly keratolytic — softens the look of rough skin. Associate…
Read the guide →Peptides
Short amino acid chains that act as signalling molecules in skin. Signalling peptides (e.g. Matrixyl/palmitoyl tripep…
Read the guide →Adenosine
Purine nucleoside naturally present in all living cells — acts as a cellular energy and signalling molecule. Supports…
Read the guide →Azelaic Acid
Dicarboxylic acid with dual exfoliating and antioxidant mechanism. Targets the look of uneven tone, and suits rosacea…
Read the guide →Bakuchiol
Plant-derived meroterpene from Psoralea corylifolia seeds. Independently activates retinoid receptors without the ret…
Read the guide →Benzoyl Peroxide
Bactericidal and keratolytic — targets C. acnes and dissolves follicular keratin. Suited to acne-prone skin. Generate…
Read the guide →Zinc PCA
Complex of zinc ion with pyrrolidone carboxylic acid. Addresses the appearance of excess sebum; suits congestion-pron…
Read the guide →Zinc Oxide
Inorganic UV filter — reflects and scatters both UVA and UVB. Broad-spectrum. Inherently photostable. Does not genera…
Read the guide →Tranexamic Acid
Synthetic amino acid derivative that interrupts the melanin-stimulation pathway at the keratinocyte level. Supports t…
Read the guide →Alpha-arbutin
Glycosylated hydroquinone derivative — inhibits tyrosinase without the irritation and photosensitivity profile of hyd…
Read the guide →Kojic Acid
Fungal-derived tyrosinase inhibitor — supports the look of more even tone. Mechanism similar to alpha-arbutin but wit…
Read the guide →Ferulic Acid
Phenolic antioxidant found in plant cell walls. Stabilizes L-ascorbic acid and vitamin E formulas — doubles antioxida…
Read the guide →Tocopherol
Fat-soluble antioxidant (vitamin E) — neutralizes free radicals in the lipid bilayer of skin. Emollient; contributes …
Read the guide →Green Tea Extract
Polyphenol-rich extract of Camellia sinensis. Primary active fraction: EGCG (epigallocatechin gallate) — one of the m…
Read the guide →Galactomyces Ferment Filtrate
Ferment filtrate from Saccharomyces fermentation used in sake production. Rich in vitamins, minerals, and amino acids…
Read the guide →Lactobacillus Ferment
Probiotic-derived active from Lactobacillus strains. Supports the look of balanced, comfortable skin. Fermentation me…
Read the guide →Snail Secretion Filtrate
Filtrate from the secretion of Cryptomphalus aspersa. Complex composition: glycoproteins, naturally occurring glycoli…
Read the guide →Caffeine
Methylxanthine derived from plant sources (coffee, tea, guarana). Applied topically, suits skin that shows the look o…
Read the guide →Resveratrol
Polyphenol stilbene — concentrated antioxidant. More photostable than L-ascorbic acid alone. Synergistic with vitamin…
Read the guide →Ascorbyl Glucoside
Stable vitamin C derivative — converts to L-ascorbic acid in skin. More shelf-stable and pH-tolerant than L-ascorbic …
Read the guide →
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