COSRX The Vitamin C 13 Serum Versus Paula's Choice C15 Super Booster

COSRX The Vitamin C 13 Serum Versus Paula's Choice C15 Super Booster

This brightening serum is formulated around Ascorbic Acid and 3-O-Ethyl Ascorbic Acid to brighten dull-looking skin and fade the look of dark spots.

This brightening serum is formulated around Ascorbic Acid and Ferulic Acid to brighten dull-looking skin and soften the look of wrinkles.

What's inside

Key Ingredients

Benefits

Concerns

Ingredients Side-by-side

Water

Ascorbic Acid 13%

Butylene Glycol

Dipropylene Glycol

Tromethamine

3-O-Ethyl Ascorbic Acid

Panthenol

Acetyl Glucosamine

Caffeine

Sodium Hyaluronate

Sodium Sulfite

Disodium EDTA

Glutathione

Adenosine

Gardenia Florida Fruit Extract

Allantoin

Dextrin

Squalane

Tocotrienols

Tocopherol

Elaeis Guineensis Oil

Arginine

Niacinamide

Pentylene Glycol

Glycyrrhiza Glabra Root Extract

Water, Ascorbic Acid 13%, Butylene Glycol, Dipropylene Glycol, Tromethamine, 3-O-Ethyl Ascorbic Acid, Panthenol, Acetyl Glucosamine, Caffeine, Sodium Hyaluronate, Sodium Sulfite, Disodium EDTA, Glutathione, Adenosine, Gardenia Florida Fruit Extract, Allantoin, Dextrin, Squalane, Tocotrienols, Tocopherol, Elaeis Guineensis Oil, Arginine, Niacinamide, Pentylene Glycol, Glycyrrhiza Glabra Root Extract

Ascorbic Acid

Propanediol

Glycerin

Ethoxydiglycol

Sodium Hydroxide

PPG-26-Buteth-26

PEG-40 Hydrogenated Castor Oil

Bisabolol

Ferulic Acid

Sodium Phytate

Decylene Glycol

1,2-Hexanediol

Sphingomonas Ferment Extract

Phenoxyethanol

Water, Ascorbic Acid, Dipropylene Glycol, Propanediol, Glycerin, Ethoxydiglycol, Sodium Hydroxide, PPG-26-Buteth-26, PEG-40 Hydrogenated Castor Oil, Bisabolol, Ferulic Acid, Sodium Phytate, Decylene Glycol, Tocopherol, 1,2-Hexanediol, Sphingomonas Ferment Extract, Phenoxyethanol

Reviews

Alternatives

Ingredients Explained

These ingredients are found in both products.

Ingredients higher up in an ingredient list are typically present in a larger amount.

Ascorbic Acid is is pure Vitamin C and is the biologically active form used directly by skin.

Not only is vitamin C great for your overall health and immune system, but it also has plenty of benefits for your skin. It is best supported by academic literature for:

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.

Dipropylene Glycol is a synthetically created humectant, stabilizer, and solvent.

This ingredient helps:

Dipropylene glycol is technically an alcohol, but it belongs to the glycol family (often considered part of the ‘good’ alcohols). This means it is hydrating and gentle on skin unlike drying solvent alcohols like denatured alcohol.

As a masking agent, Dipropylene Glycol can be used to cover the smell of other ingredients. However, it does not have a scent.

Studies show Dipropylene Glycol is considered safe to use in skincare.

Tocopherol is a fat-soluble antioxidant known as Vitamin E.

You'll find this ingredient in the vast majority of skincare (for good reason). It works to neutralize free radicals, or unstable molecules generated by UV exposure, pollution, and other environmental stressors, before they can cause oxidative damage to your skin cells.

Topically applied tocopherol has been shown to protect against UV damage by ramping up the skin's own natural defense enzymes.

It also acts as a skin conditioning agent; some studies show that regular topical use can improve the skin's water-binding capacity over 2-4 weeks.

This ingredient is especially loved for being a team player. When combined with Vitamin C, the photoprotective effect of both ingredients roughly doubles and the combo also helps reduce UV-induced DNA damage.

This ingredient has some brightening potential but it's more of a prevention ingredient than spot-fader. Cell studies show it can slow down melanin production but it's worth noting that it's not the most powerful brightener out there.

In formulations, it also serves as a stabilizer that helps protect other oxidation-prone ingredients from degrading.

Concentrations usually range from 0.1-1% in most leave-on products.

Water. It's the most common cosmetic ingredient of all. You'll usually see it at the top of ingredient lists, meaning that it makes up the largest part of the product.

So why is it so popular? Water most often acts as a solvent - this means that it helps dissolve other ingredients into the formulation.

You'll also recognize water as that liquid we all need to stay alive. If you see this, drink a glass of water. Remember to stay hydrated!

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