How much vitamin C (LAA) do you need? 5%+

What vitamin C (LAA) percentage is effective?

The floor is 5%: a 5% L-ascorbic acid cream beat its excipient on a dermatologist global score, silicone-replica microrelief and elastic-fibre ultrastructure over 6 months on the neck and forearms of photoaged women (Humbert 2003, double-blind; the abstract gives no headcount).

Is 23% vitamin C (LAA) too much?

Nobody has measured it: no published dose comparison sets a ceiling for vitamin C (LAA), so 23% is above the 5% floor the trials used, not above a measured maximum, and the trials say nothing about whether more does more. The highest dose tested in leave-on use was 25% in an open-label melasma study, with a penetration enhancer (Hwang 2009), and the paper does not say how skin tolerated it.

No published dose comparison sets a ceiling for vitamin c (laa). A declared percentage above 5% is above the trials' floor, not above a measured maximum: the trials say from 5% it works, and say nothing about whether more does more.

What does the vitamin C (LAA) percentage on a label tell you?

A name that states a percentage ("Vitamin C (LAA) 5%") is the only amount a cosmetic label ever declares, so it is the one number that can be read against the trials: at or above the 5% floor, or below it.

A name without a percentage leaves the position. The rules make a brand list ingredients in descending order of amount down to 1%, and in any order below it, so vitamin c (laa) above the 1% line is at least 1% and vitamin c (laa) below it can be any trace the brand likes. The floor the trials worked from is 5%, and a position alone cannot tell you whether a label reaches it.

The vitamin C (LAA) percentages in our catalogue

One label declares a percentage on the name, read against the trials:

• The Ordinary Vitamin C Suspension 23% + HA Spheres 2%Vitamin C (LAA) is declared at 23%: above the 5% the trials used.

4 labels carry it without a number, so the position is all there is:

• Round Lab Birch Juice Moisturizing Sun CreamVitamin C (LAA) sits 29th of 40, below the 1% line; the label does not say how much, and the trials worked from 5%.
• ISDIN Fotoprotector Fusion Water SPF 50Vitamin C (LAA) sits 28th of 29, below the 1% line; the label does not say how much, and the trials worked from 5%.
• LANEIGE Lip Sleeping Mask (Berry)Vitamin C (LAA) sits 27th of 34, below the 1% line; the label does not say how much, and the trials worked from 5%.
• Celimax The Vita A Retinal Shot Tightening BoosterVitamin C (LAA) sits 29th of 32, below the 1% line; the label does not say how much, and the trials worked from 5%.

Read on

• Vitamin C (LAA): the glossary page what it does, who it suits, where it fits
• Vitamin C (LAA) vs Niacinamide
• Vitamin C (LAA) vs Retinol
• Vitamin C (LAA) vs Retinal
• Vitamin C (LAA) vs Hydroxypinacolone Retinoate
• Vitamin C (LAA) vs Retinyl Palmitate
• Vitamin C (LAA) vs Retinyl Acetate

Other actives with a dose the trials pinned:

• Niacinamide 2%+
• Retinol 0.075 to 0.3%
• Salicylic acid (BHA) 0.5%+
• Lactic acid 8%+
• Glycolic acid 5%+
• Retinal 0.05 to 0.1%
• Retinyl Retinoate 0.06%+
• Tretinoin 0.025%+
• Adapalene 0.1%+
• Tazarotene 0.045%+
• Azelaic Acid 15%+
• THD Ascorbate 1%+
• Sodium Ascorbyl Phosphate 5%+
• Palmitoyl Pentapeptide-4 0.0003%+
• Caffeine 2%+
• Benzoyl Peroxide 2.5 to 5%
• Tea Tree Oil 5%+
• Hydroquinone 4%+
• Bifida Ferment Lysate 10%+
• Thiamidol 0.2%+
• Cysteamine 5%+
• Menthol 0.1 to 5%
• Peppermint Oil 0.5%+
• N-Acetyl Glucosamine 2%+
• Alpha Lipoic Acid 5%+
• Ammonium lactate 12%+
• Acetylated Hyaluronic Acid 0.1%+
• 4-n-Butylresorcinol 0.1%+
• 4-t-Butylcyclohexanol 0.4%+
• Sphingomonas Ferment Extract 2%+