Principia Sérum Facial αA-2 Versus The INKEY List Alpha Arbutin Serum

Principia Sérum Facial αA-2 Versus The INKEY List Alpha Arbutin Serum

This brightening serum is formulated around Gluconolactone and Alpha-Arbutin to fade the look of dark spots and brighten dull-looking skin.

This brightening serum is formulated around Alpha-Arbutin to fade the look of dark spots and brighten dull-looking skin.

What's inside

Key Ingredients

Benefits

Concerns

No concerns

Ingredients Side-by-side

Water

Xanthan Gum

Propanediol

Disodium EDTA

Sodium Hyaluronate

Gluconolactone

Alpha-Arbutin

Phenoxyethanol

Caprylyl Glycol

Water, Xanthan Gum, Propanediol, Disodium EDTA, Sodium Hyaluronate, Gluconolactone, Alpha-Arbutin, Phenoxyethanol, Caprylyl Glycol

Butylene Glycol

Glycerin

Dicaprylyl Carbonate

Caprylic/Capric Triglyceride

Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer

Squalane

Phospholipids

Glycine Soja Oil

Carbomer

Polysorbate 60

Sodium Phytate

Glycolipids

Sorbitan Isostearate

Leuconostoc/Radish Root Ferment Filtrate

Sodium Hydroxide

Glycine Soja Sterols

Hyaluronic Acid

Tocopherol

Water, Butylene Glycol, Propanediol, Glycerin, Alpha-Arbutin, Dicaprylyl Carbonate, Caprylic/Capric Triglyceride, Phenoxyethanol, Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer, Caprylyl Glycol, Squalane, Phospholipids, Glycine Soja Oil, Carbomer, Polysorbate 60, Sodium Phytate, Glycolipids, Sorbitan Isostearate, Leuconostoc/Radish Root Ferment Filtrate, Sodium Hydroxide, Glycine Soja Sterols, Hyaluronic Acid, Tocopherol

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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.

Alpha-Arbutin is a brightening active used to fade dark spots, melasma, and post-acne marks. Structurally, it is a hydroquinone with a sugar molecule attached (but is much gentler than raw hydroquinone).

It has a pretty elegant way of working; it slots into tyrosinase, or the key enzyme that your skin uses to make melanin), and competitively blocks it so your skin produces less pigment over time.

There are two forms of arbutin and alpha is the better one to reach for: it works at lower amounts, absorbs into skin more easily, and has a strong safety record.

The science backs this up too: lab and animal studies confirm it lowers melanin by blocking tyosinase and the more you use (up to a point), the more it works.

Human studies look good too.

A 2024 trial found a cream with 5% alpha-arbutin and 2% kojic acid worked about as well as a prescription melasma cream but with fewer side effects. Another study showed 2% alpha-arbutin paired with 10% Trihydroxybenzoic Acid Glucoside and sunscreen faded dark spots and melasma without causing irritation.

Concentration-wise, most serums land in the 1-2% range.

The EU's Scientific Committee on Consumer Safety concluded that alpha-arbutin is safe in face creams up to 2% and body lotions up to 0.5%.

Overall, this is a well-studied and low-irritation brightener that's a great pick for anyone dealing with uneven skin tone. It also pairs well with vitamin C, niacinamide, and sunscreen.

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.

Propanediol is an all-star ingredient. It softens, hydrates, and smooths the skin.

It’s often used to:

Propanediol is not likely to cause sensitivity and considered safe to use. It is derived from corn or petroleum with a clear color and no scent.

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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