Kiehl's Ultra Pure High-Potency 1.5% Hyaluronic Acid Serum Versus Naked & Thriving Renew Resurfacing Night Serum

Kiehl's Ultra Pure High-Potency 1.5% Hyaluronic Acid Serum Versus Naked & Thriving Renew Resurfacing Night Serum

This hydrating serum is formulated around Sodium Hyaluronate to hydrate skin and strengthen the skin barrier.

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

What's inside

Key Ingredients

Benefits

Concerns

Ingredients Side-by-side

Water

Glycerin

Sodium Hyaluronate

Phenoxyethanol

Chlorphenesin

Tetrasodium Glutamate Diacetate

Citric Acid

Water, Glycerin, Sodium Hyaluronate, Phenoxyethanol, Chlorphenesin, Tetrasodium Glutamate Diacetate, Citric Acid

Aloe Barbadensis Leaf Juice

Propanediol

Vaccinium Myrtillus Fruit Extract

Saccharum Officinarum Extract

Terminalia Ferdinandiana Fruit Extract

Citrus Aurantium Dulcis Fruit Extract

Ferulic Acid

Citrus Limon Fruit Extract

Pentylene Glycol

Acer Saccharum Extract

Phenethyl Alcohol

Water, Aloe Barbadensis Leaf Juice, Glycerin, Sodium Hyaluronate, Propanediol, Vaccinium Myrtillus Fruit Extract, Saccharum Officinarum Extract, Terminalia Ferdinandiana Fruit Extract, Citrus Aurantium Dulcis Fruit Extract, Ferulic Acid, Citrus Limon Fruit Extract, Pentylene Glycol, Acer Saccharum Extract, Phenethyl Alcohol, Citric Acid

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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.

Citric Acid is an alpha hydroxy acid (AHA) naturally found in citrus fruits like oranges, lemons, and limes.

Like other AHAs, citric acid can exfoliate skin by breaking down the bonds that hold dead skin cells together. This helps reveal smoother and brighter skin underneath.

However, this exfoliating effect only happens at high concentrations (20%) which can be hard to find in cosmetic products.

Due to this, citric acid is usually included in small amounts as a pH adjuster. This helps keep products slightly more acidic and compatible with skin's natural pH.

In skincare formulas, citric acid can:

While it can provide some skin benefits, research shows lactic acid and glycolic acid are generally more effective and less irritating exfoliants.

Most citric acid used in skincare today is made by fermenting sugars (usually from molasses). This synthetic version is identical to the natural citrus form but easier to stabilize and use in formulations.

Rosacea skin has a lower threshold for acids generally, with 62.5% of rosacea subjects in one study reacting to lactic acid in a sting test. This is why we mark citric acid as a potential rosacea trigger.

However, this ingredient shows up as a pH adjuster or chelator at roughly 0.1-1% in many products. These low levels are unlikely to be an issue for rosacea skin and becomes a potential trigger at exfoliating concentrations (20%). Because everybody's skin is unique, we recommend a patch test if you are unsure.

Glycerin (or glycerol) is a compound naturally found in your skin. It's a powerhouse humectant that pulls water into the stratum corneum.

Topically, glycerin does several things at once:

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.

Sodium Hyaluronate is the salt form of hyaluronic acid. It is a long sugar chain that is naturally found in your skin, joints, and connective tissue that maintains hydration and elasticity.

In skincare, it works as a humectant. It pulls water from the environment and deeper layers of skin and binds it to the surface.

Interestingly, the size of the molecule affects its behavior:

Some clinical evidence links low molecular weight versions to improved wrinkle depth, elasticity, anti-inflammatory effects, and barrier repair.

Many serums use a blend of both weights so you can get surface hydration plus longer-lasting and deeper effects.

You'll typically see concentrations between 0.1-2% for this ingredient.

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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