PrescriptSkin Enhanced Brightening Toner Versus Numbuzin No.5 Glutathione Vitamin Concentrated Toner

In a formula, it does the 3 classic vitamin C jobs: it acts as an antioxidant, helps brighten skin tone by inhibiting tyrosinase, and supports collagen.

The evidence is reasonably solid for a cosmetic ingredient; Liao and colleagues (2018) showed it's significantly more stable than ascorbic acid while still being effective.

A 2021 study by Zerbinati and colleagues tested a serum with 30% 3-O-ethyl-l-ascorbic acid and 1% lactic acid significantly increased collagen production, reduced UVB-induced DNA damage, and decreased melanin on a reconstructed pigmented skin model.

Typical real world usage sits around 0.5-5% (and 1-2% is common for daily serums).

Amounts up to 30% have been shown to be non-irritating on human skin samples, but two isolated cases reported allergic contact dermatitis so a patch test is sensible if you have reactive skin.

Topical vitamin C has been shown to help neutralize oxidative stress from UV and pollution, helping to improve photoaging and hyperpigmentation when used consistently.

One clinical study found that using 5% topical vitamin C for six months improved signs of photodamaged skin, both on the surface and in the deeper structural layers of the skin.

While vitamin C doesn’t replace sunscreen, studies show it can boost photoprotection when combined with Vitamin E and ferulic acid. These two ingredients help improve stability and protective effects.

The big downside of this ingredient is formulation difficulty. Vitamin C is prone to oxidation and doesn't penetrate the skin unless formulated correctly. Research found that vitamin C absorbs into the skin best at a low pH (< 3.5) with about 20% being the upper limit for effective absorption.

Skin levels can saturate after repeated application; this means your skin won’t keep absorbing more once it’s full of vitamin C. This is why more isn’t always better with vitamin C and why very high concentrations don’t necessarily give extra benefits.

Ascorbic acid generally works well with many skincare ingredients but can be irritating when combined with other active ingredients. Strong oxidizing acne treatments like benzoyl peroxide can reduce the effectiveness of vitamin C if they are used at the same time; they are often recommended for use at different times of day.

Read more about other types of Vitamin C:

Foods rich with vitamin C include oranges, strawberries, broccoli, bell peppers, and more. When consuming Vitamin C, your skin receives a portion of the nutrients.

Your skin makes glycerin on its own (mostly from sebaceous oil breakdown) and shuttles it to your outermost layer of skin, or your epidermis, via aquaporin-3.

Aquaporin-3 is a transporter that is essential for normal skin hydration, elasticity, and repair. Interestingly, mice lacking in AQP3 have dry and less elastic skin that can be fully corrected with glycerin.

This ingredient is non-irritating, plays well with almost every ingredient, and works across all skin types. Typical use is anywhere between 3-10% but can go up to 79% in some leave-on products.

Just know very high concentrations (>40%) can feel tacky in low humidity.

Glycerin is the name for this ingredient in American English. British English uses Glycerol/Glycerine.