Skin science article
Allies of Skin 35% Vitamin C+ Perfecting Serum Versus Sunday Riley C.E.O. 15% Vitamin C Brightening Serum
Allies of Skin 35% Vitamin C+ Perfecting Serum Versus Sunday Riley C.E.O. 15% Vitamin C Brightening Serum This brightening serum is formulated around 3-O-Ethyl Ascorbic Acid and Tetrahexyldecyl Ascorbate to brighten dull-looking skin and fade the look of dark
Allies of Skin 35% Vitamin C+ Perfecting Serum Versus Sunday Riley C.E.O. 15% Vitamin C Brightening Serum
This brightening serum is formulated around 3-O-Ethyl Ascorbic Acid and Tetrahexyldecyl Ascorbate to brighten dull-looking skin and fade the look of dark spots.
This brightening serum is formulated around Tetrahexyldecyl Ascorbate and Glycolic Acid to brighten dull-looking skin and refine skin texture.
What's inside
Key Ingredients
Benefits
Concerns
No concerns
Ingredients Side-by-side
Ethoxydiglycol
3-O-Ethyl Ascorbic Acid
Tetrahexyldecyl Ascorbate
Dimethyl Isosorbide
Isodecyl Neopentanoate
Glutathione
Superoxide Dismutase
Ethylhexylglycerin
Caprylyl Glycol
Phenoxyethanol
Ethoxydiglycol, 3-O-Ethyl Ascorbic Acid, Tetrahexyldecyl Ascorbate, Dimethyl Isosorbide, Isodecyl Neopentanoate, Glutathione, Superoxide Dismutase, Ethylhexylglycerin, Caprylyl Glycol, Phenoxyethanol
Water
Squalane
Polyglyceryl-6 Distearate
PEG-8 Beeswax
PPG-12/Smdi Copolymer
Glycine Soja Sterols
Sodium Phytate
Tocopherol
Acetamidoethoxyethanol
Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer
Sodium Acrylate/Sodium Acryloyldimethyl Taurate Copolymer
Jojoba Esters
Glycolic Acid
Cetyl Alcohol
Polyglyceryl-3 Beeswax
Chlorphenesin
Glycerin
Polysorbate 60
Sorbitan Isostearate
Saccharide Isomerate
Citrus Aurantium Dulcis Peel Oil
Citrus Tangerina Peel Oil
Linalool
Limonene
Water, Tetrahexyldecyl Ascorbate, Squalane, Polyglyceryl-6 Distearate, PEG-8 Beeswax, PPG-12/Smdi Copolymer, Glycine Soja Sterols, Sodium Phytate, Tocopherol, Acetamidoethoxyethanol, Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer, Sodium Acrylate/Sodium Acryloyldimethyl Taurate Copolymer, Jojoba Esters, Glycolic Acid, Caprylyl Glycol, Cetyl Alcohol, Polyglyceryl-3 Beeswax, Chlorphenesin, Glycerin, Polysorbate 60, Sorbitan Isostearate, Saccharide Isomerate, Citrus Aurantium Dulcis Peel Oil, Citrus Tangerina Peel Oil, Linalool, Limonene, Phenoxyethanol
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Alternatives
Ingredients Explained
These ingredients are found in both products.
Ingredients higher up in an ingredient list are typically present in a larger amount.
Caprylyl Glycol is a humectant, skin conditioner, emollient, and preservative booster derived from either caprylic acid or synthetically created.
Typical use levels vary from 0.3-1% as a preservative booster and go up to 2% to condition skin.
Because it is not a free-fatty acid, this ingredient is fungal acne safe (there's nothing for Malassezia to feed on).
Phenoxyethanol is one of the most widely used preservatives in skincare (and for good reason!).
It has a large spectrum of antimicrobial activity and especially effective bacteria, yeast, and mold while only having a weak effect on your skin's natural microbiome.
On a cellular level, it disrupts the cell membranes of microbes by poking holes that make the cell leak. This shuts down the chemical reactions the microbe needs to make energy so it can no longer survive.
Another perk of this ingredient is that it stays functional across a wide pH range (3-10).
You'll often see it paired with boosters like Ethylhexylglycerin; one study showed that a 1:9 ratio of Ethylhexylglycerin to Phenoxyethanol damages bacterial membranes as effectively as doubling the Phenoxyethanol concentration on its own.
Typical use concentrations range from 0.3-1% depending on the formula, and this ingredient is capped at 1% int the EU.
Safety-wise, the fear mongering does not hold up to the evidence. The EU's Scientific Committee on Consumer Safety and FDA consider it safe as a preservative at up to 1%, including for children of all ages.
Adverse systemic effects only showed up in animal studies at exposures roughly 200x higher than what people get from cosmetics. And despite its very widespread use, this ingredient is a rare sensitizer and allergic reactions are uncommon.
Tetrahexyldecyl Ascorbate (THD) is a stable and oil-soluble form of Vitamin C.
THD is special in that it has the ability to travel deeper into skin than traditional ascorbic acid while maintaining the same skin benefits (double win!).
Because it’s oil-soluble, THD dives deep into your skin’s fatty layers (think ceramides and cholesterol) to fight off the kind of free radicals that mess with your skin barrier. This makes it a great pair with water-based vitamin C (ascorbic acid) that mainly works on the surface.
Even at just 0.1%, THD is already showing great antioxidant activity. When used up to 2%, it helps keep your skin happy and calm, especially when it’s stressed from pollution or sun.
Want to fade dark spots or tackle hyperpigmentation? You’ll want 5% or more. Pairing it with brightening buddies like niacinamide or licorice root gives even better results. One study even used 30% THD with other brighteners and saw real results on stubborn discoloration, even in melasma-prone skin.
A note on THD: It’s has a slightly silky, oily texture and usually shows up colorless or pale yellow (though the exact shade can vary by supplier).
While you can sneak it into water-based formulas, it really shines when paired with silicones or oils, which help your skin soak it up better.
THD is pretty stable, but it’s still vulnerable to degradation like ascorbic acid. Too much light or heat (above 113°F / 45°C) can break it down over time. Go for dark and opaque packaging that keeps it safe and shady!
Read more about other types of Vitamin C: