Formula · 7.4

Brand · 7.3

COSRX · ascorbic acid 23% · South Korea

COSRX The Vitamin C 23 Serum

COSRX The Vitamin C 23 Serum
7.4

LabReadAI label score

How the score is calculated
  • Actives and evidence0.6Actives with strong evidence: 2 of 9
  • Active concentration1.0After the 1 % line: niacinamide (vitamin b3), caffeine, licorice extract, camellia oil — the concentration is likely token
  • Completeness for the purpose0.6For “dark spots and uneven tone” — 57 %; retinoid; glycolic acid; could be added without conflict: retinoid, glycolic acid; a broad formula across 7 purposes
  • Tolerance0.9Above the tolerance threshold: Vitamin C — irritation more likely
  • adults
  • pregnancyallowed per the leaflet
  • oily skin
  • acne-prone
  • dry skin
  • atopic skin
  • children
  • babies
  • sensitive skinstings at 15–20 %
  • rosaceaask a dermatologist
Free from:
  • alcohol (alcohol denat) · by the listthe list has no ingredient of the “denatured alcohol” group — evaporates fast and degreases; frequent contact can dry the skin — a tolerance question, not a regulatory one; does not clog pores
  • sulfates (SLS/SLES) · by the listthe list has no ingredient of the “ammonium laureth sulfate (ALES), ammonium lauryl sulfate (ALS), sodium coco-sulfate, sodium laureth sulfate (SLES), sodium lauryl sulfate (SLS), sodium myreth sulfate, TEA-lauryl sulfate” group — a cleansing surfactant from the sulfate family but with an ethoxylated chain: it cleanses more gently than lauryl sulfate. Still not for those looking for a sulfate-free product.
  • formaldehyde releasers · by the listthe list has no ingredient of the “formaldehyde releasers” group — preservatives that slowly release formaldehyde; allowed at low levels but a frequent cause of contact allergy
  • isothiazolinones (MIT/MCI) · by the listthe list has no ingredient of the “isothiazolinone preservatives (MIT/MCI)” group — preservatives; banned in EU leave-on products and limited in rinse-off (0.0015%) — a frequent cause of contact allergy
  • fragrance · by the listthe list has no ingredient of the “fragrance and its allergens” group — the fragrance and its aromatic components; the EU requires 26 of them to be listed separately — matters to people allergic to fragrance, does not affect how the product works
  • parabens · by the listthe list has no ingredient of the “parabens” group — preservatives; methyl- and ethylparaben are recognised as safe at permitted levels, propyl- and butyl- are limited by the EU to 0.14 %; a frequent buyer question rather than proven harm
  • mineral oils and petrolatum · by the listthe list has no ingredient of the “petrolatum and mineral oils” group — purified cosmetic-grade petroleum products: form a protective barrier film; safety is established, a preference question; 0–2 of 5 (depends on the raw-material source), cosmetic white oil per DiNardo (2005) is non-comedogenic
  • soap · by the listthe list has no ingredient of the “potassium soap (potassium cocoate), plant soap base (sodium palmate, sodium cocoate), tallow soap base (sodium tallowate)” group — liquid soap: fatty acids boiled with alkali. It cleanses well, but its acidity is around 9-10 against 5 for skin, which is why it often leaves tightness. The product is rinsed off, so the question is tolerance.
  • gelatin in the coating · by the listthe list has no ingredient of the “vegetarian coating” group — a plant-based tablet coating instead of gelatin; it keeps moisture out and makes swallowing easier
  • toning dyes · by the listthe list has no ingredient of the “violet toning dyes” group — direct dyes that settle on the hair surface and cancel the yellow cast of blonde; they wash out in 1–3 washes and leave a lilac tint if left too long; HC Blue 2 and Disperse Violet 1 are known contact allergens of hair dyes
  • tar · by the listthe list has no ingredient of the “wood (birch) tar” group — a traditional remedy for dandruff and itching with a sharp smell; it reduces flaking, but can irritate a sensitive scalp and dries the hair
What for: Against dark spots you need two fronts: actives that slow pigment production (azelaic and tranexamic acids, niacinamide, vitamin C, arbutin, thiamidol) and those that speed up skin renewal (a retinoid, acids). One active per front is enough; better both fronts and SPF in the daytime.
When:
  • leave-on
  • morning
in the morning under SPF
When to expect an effect: tone, glow — 4–8 weeks; tone, pores — 4–8 weeks; sebum — 2–4; softness — right away; dryness — 1–2 weeks; puffiness — within an hour, briefly; dark circles — no effect to expect; wrinkles — 8 weeks, a modest effect; soothing and less tightness — within days; soothing — days; barrier — 2–4 weeks; redness, itching — 1–2 weeks; spots — 8–12 weeks, if at all; shine and softness — immediately, while the oil is on the hair
What is normal: stinging at high concentration; mild flushing in the first days at high concentration; nothing special — well tolerated; weighs fine hair down when overused

Ingredients — 28 components · 9 work

What works: 9 of 28 ingredients: vitamin c, niacinamide, squalane and 6 more. Against dark spots you need two fronts: actives that slow pigment production (azelaic and tranexamic acids, niacinamide, vitamin C, arbutin, thiamidol) and those that speed up skin renewal (a retinoid, acids). One active per front is enough; better both fronts and SPF in the daytime.

Strengths: active concentration, tolerance

What lowers the score: actives and evidence: actives with strong evidence: 2 of 9; completeness for the purpose: for “dark spots and uneven tone” — 57 %

Questions: no debatable ingredients in the formula

  • Niacinamide (vitamin B3) + Vitamin C — reinforce each otherthe niacinamide–vitamin C “conflict” is a myth: conversion to nicotinic acid happens only with heat and long storage; in cosmetics they are compatible and both work against pigment
  • Aqua/Water base: coating, fillers · water — the solvent and base; listed first because there is more of it than anything else; in supplements — part of the capsule shell
  • Ascorbic Acid (23% works · the active ingredient — what the product is for; form: ascorbic acid
  • Butylene Glycol base: coating, fillers · a humectant and solvent: it makes the texture lighter and helps actives spread. Better tolerated than propylene glycol.
  • Dimethicone base: coating, fillers · form a smooth film and shine; inert and not absorbed — a preference question, not a safety one
  • Panthenol works · the active ingredient — what the product is for; form: panthenol
  • 3-O-Ethyl Ascorbic Acid works · the active ingredient — what the product is for; form: ascorbic acid
  • Squalane works · the active ingredient — what the product is for; form: squalane (saturated, from olive or sugarcane)
  • Sodium Hydroxide base: coating, fillers · tune the acidity and texture; salt is a common shampoo thickener
  • Caffeine works · the active ingredient — what the product is for; form: caffeine
  • Sodium Hyaluronate label wording · an allergen (sodium (salt)) — matters when limiting salt, for example with blood pressure; the label says it is absent
  • Sodium Metaphosphate label wording · an allergen (sodium (salt)) — matters when limiting salt, for example with blood pressure; the label says it is absent
  • Adenosine works · the active ingredient — what the product is for; form: adenosine
  • Acetyl Glucosamine base: coating, fillers · softens the skin and helps it hold water — the most common role in creams
  • Gardenia Florida Fruit Extract base: coating, fillers · softens the skin and helps it hold water — the most common role in creams
  • Allantoin works · the active ingredient — what the product is for; form: allantoin
  • Dextrin base: coating, fillers · a starch breakdown product: a filler, thickener and film former; does not act
  • Tocotrienols base: coating, fillers · vitamin E at hundredths of a percent: keeps the oils of the formula (a cream or a capsule fill) from going rancid; at that share it protects the product, it is not vitamin E as an active
  • Tocopherol base: coating, fillers · vitamin E at hundredths of a percent: keeps the oils of the formula (a cream or a capsule fill) from going rancid; at that share it protects the product, it is not vitamin E as an active
  • Elaeis Guineensis (Palm) Oil base: coating, fillers · the plant base: emollient oils, waxes and care extracts
  • Arginine base: coating, fillers · amino acids, lipids and sugars akin to the skin’s own components — support for its barrier
  • Niacinamide works · the active ingredient — what the product is for; form: niacinamide
  • Pentylene Glycol base: coating, fillers · humectants and solvents — hold water and help actives dissolve
  • Glutathione base: coating, fillers · breaks chemical bonds — how perm products work
  • Helianthus Annuus (Sunflower) Seed Oil base: coating, fillers · a light emollient oil rich in linoleic acid (in tablets — a coating component); does not clog pores
  • Methyl Trimethicone base: coating, fillers · makes hair softer and easier to comb
  • Carthamus Tinctorius (Safflower) Seed Oil base: coating, fillers · a light oil rich in linoleic acid; among the least comedogenic — does not clog pores
  • Camellia Japonica Seed Oil works · the active ingredient — what the product is for; form: seed oil
  • Daucus Carota Sativa (Carrot) Root Extract base: coating, fillers · softens the skin and helps it hold water — the most common role in creams
  • Glycyrrhiza Glabra (Licorice) Root Extract works · the active ingredient — what the product is for; form: licorice root extract
  • Beta-Carotene base: coating, fillers · softens the skin and helps it hold water — the most common role in creams

COSRX The Vitamin C 23 Serum is a product whose active ingredient is vitamin c + niacinamide (vitamin b3) + squalane + caffeine at a declared 23 %. The effect is supported by studies: vitamin c, niacinamide (vitamin b3). There is little evidence of effect: squalane, caffeine, adenosine, licorice extract, camellia oil. The effect is moderately supported: allantoin, panthenol (pro-vitamin b5). The formula has 28 ingredients, 9 of which do the work; the rest is the formula base. Well-matched pairs in the formula: niacinamide (vitamin b3) + vitamin c. Against dark spots you need two fronts: actives that slow pigment production (azelaic and tranexamic acids, niacinamide, vitamin C, arbutin, thiamidol) and those that speed up skin renewal (a retinoid, acids). One active per front is enough; better both fronts and SPF in the daytime. By the list, no alcohol (alcohol denat), sulfates (SLS/SLES), formaldehyde releasers, isothiazolinones (MIT/MCI), fragrance, parabens, mineral oils and petrolatum, soap, gelatin in the coating, toning dyes, tar. Suitable for: adults, pregnancy, oily skin, acne-prone, dry skin, atopic skin, children, babies. sensitive skin, rosacea — ask a doctor. Use: in the morning under SPF. When to expect an effect: tone, glow — 4–8 weeks. Label score — 7.4 out of 10 (actives with strong evidence: 2 of 9; after the 1 % line: niacinamide (vitamin b3), caffeine, licorice extract, camellia oil — the concentration is likely token; for “dark spots and uneven tone” — 57 %; retinoid; glycolic acid; could be added without conflict: retinoid, glycolic acid; a broad formula across 7 purposes; above the tolerance threshold: vitamin c — irritation more likely). The brand states: start with once-daily use; sun protection is required in the daytime afterwards. 23% is above the 10–20% range in which ascorbic acid has been studied: skin uptake does not grow above 20%, while stinging and redness become more common.

Who it does not suit

When to stop: persistent redness — stop; a darkened serum has oxidised; persistent burning — stop; new comedones — stop; itching, rash — stop

Per the maker's leaflet: The brand states: start with once-daily use; sun protection is required in the daytime afterwards. 23% is above the 10–20% range in which ascorbic acid has been studied: skin uptake does not grow above 20%, while stinging and redness become more common.

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