A reader emailed me in January with a question I get every six weeks or so. She had cut her shelf from fourteen products to five, dropped sheet masks, dropped the second cleanser she did not need, and was about to drop her first-essence. Her question was whether the essence was doing anything or whether it was the step she could finally retire after eleven years of using one.
I told her not to drop it, and I will tell you why.
First-essence (the watery, slightly viscous step that goes on right after cleansing and toning, before serums) is the K-beauty step that has survived every trend cycle I have watched since I started writing about skincare. Glass skin came and went. Seven-skin came and went. Slugging came in from K-beauty, got pulled into TikTok, and came back out the other side as a debated rather than a foundational step. Cushion compacts came, stayed, mutated. Sheet masks are now half a habit and half a ritual. But first-essence has stayed in the routine of every Korean dermatologist, every long-time K-beauty user, and almost every skin-minimalist I trust, including mine.
The reason is not what most product copy tells you. It is not “hydration”. The hydration argument is partial and a bit lazy. The real reason is closer to what SK-II has been quietly saying since 1980, which is that fermented filtrates do something to the stratum corneum that water-plus-humectant alone does not. Whether that “something” is large or small is a separate question I will get to.
What the studies actually show
The original Pitera story (which is the marketing name SK-II uses for its galactomyces ferment filtrate) is rooted in a 1970s observation that sake brewery workers had unusually well-conditioned hands despite chronic exposure to ethanol and water. SK-II screened around 350 yeast strains and isolated what they called Pitera, a fermented filtrate of Galactomyces. The brand-funded literature on this is, predictably, brand-funded. I want to flag that upfront.
The independent literature is more interesting. Kim et al. published a 2014 paper in the Journal of Microbiology and Biotechnology on fermented Galactomyces filtrate (broadly searchable, the methodology was clean) showing measurable effects on filaggrin and aquaporin-3 expression in cultured keratinocytes. Filaggrin is the protein that breaks down into natural moisturising factor (NMF) in the corneocytes. Aquaporin-3 is the water-and-glycerol channel that moves hydration through the epidermis. Both being upregulated by a topical ferment is a more mechanistic claim than “it hydrates”.
Park et al. in 2017 (Journal of Cosmetic Dermatology) looked at fermented yeast extracts more broadly, including saccharomyces and galactomyces ferments, and documented antioxidant activity and stratum corneum hydration improvements that were measurably larger than the equivalent unfermented substrate. The effect size was modest. I want to be precise about that. We are not talking about retinoid-level changes. We are talking about a small-to-moderate improvement in corneocyte hydration and a small improvement in barrier markers over four to eight weeks.
The mechanism the literature points toward is that fermentation produces a soup of small molecules (organic acids, free amino acids, polyols, B vitamins, peptide fragments) that are too small and too varied to credit to a single active. The ferment is the active. This is unusual in cosmetic chemistry, where we are usually trying to isolate one molecule.
The part most reviews skip
Most reviews of first-essences focus on texture and “glow” and miss two technical points that I think matter more.
The first is osmolarity. Watery essences applied to freshly cleansed skin sit on a stratum corneum that has been transiently disrupted by surfactant, has lost some of its NMF to the rinse water, and is in a brief window of higher permeability. What you put on the skin in that window matters more than what you put on it twenty minutes later when the barrier has resealed. Sasaki and colleagues have published on this transient permeability window for years. A first-essence with humectants, small peptides, and fermented filtrate components is, in theory, exploiting that window. A serum that hits the skin five minutes later is hitting a partially resealed barrier.
The second is the cumulative-occlusion logic of the K-beauty layering order. Each step in a multi-step K-beauty routine is meant to deliver a thinner, less occlusive payload first, with the more occlusive payloads later. First-essence is the watery delivery vehicle for ingredients that would either feel bad or fail to penetrate if you tried to deliver them in a heavier vehicle. If you skip it, you have either skipped those ingredients entirely or pushed them into your serum step where they are competing with whatever else is in there.
This is partly why I never trust the “first-essence is just expensive water” argument. The water is doing real work as a vehicle. Whether you need the specific ferment-filtrate component on top of that is a separate question.
The contrarian view I hold
Here is where I will push back on the K-beauty community a little.
I do not think most people need a hundred-and-eighty-dollar bottle of SK-II Facial Treatment Essence to get the benefit of fermented filtrates on their skin. The Pitera literature is interesting but the formulation is not unique anymore. Missha’s Time Revolution First Treatment Essence, which sits at roughly a fifth of the price, contains a 90%+ saccharomyces ferment filtrate. COSRX’s Galactomyces 95 Tone Balancing Essence is closer to the original Galactomyces species and is priced for ordinary people. Beauty of Joseon’s Ginseng Essence Water uses a ginseng ferment that has its own (much smaller but real) supporting literature.
I cannot prove that any of these is bioequivalent to SK-II’s Pitera. The brand-controlled literature is the only direct comparison data and I do not particularly trust it. What I can say is that the published effect sizes for galactomyces and saccharomyces ferments are in the same modest range across studies, regardless of brand. If you are spending two hundred dollars on a single essence and feeling guilty about it, I would tell you that the marginal benefit over a thirty-dollar ferment essence is probably not as large as the marketing implies. If you are spending thirty dollars and wondering whether the upgrade is worth it, I would tell you the same thing in reverse.
The trend overhauls (glass skin, slugging, skin cycling, “no-routine” routines, barrier-first routines) come and go because they are mostly delivery formats, not new chemistry. First-essence is the step that does not depend on any of those formats. It works in a slugging routine. It works in a barrier-repair routine. It works in skin cycling. It works in a five-step routine and a fifteen-step routine.
That is what I mean by “survives every overhaul”.
What I would tell my past self
If I could go back to the version of me who started using first-essence because a Korean beauty editor told me to, and who did not know why, I would say three things.
The ferment matters more than the brand. Pick a galactomyces, saccharomyces, or bifida ferment with a high concentration (most label this in the name or the first three ingredients). Skip the ones that hide a 0.1% ferment behind ten lines of glycerin and propanediol.
Apply it within sixty seconds of patting your face dry, while the stratum corneum is still in the transient permeability window. This is unglamorous and not what the bottle says, but it is what the literature points toward.
Do not expect retinoid-level results. Expect a small-to-moderate improvement in skin hydration, a slight improvement in how serums layer on top, and (in my own n-of-1 experience, which I cannot generalise) a softening of fine texture over months rather than weeks.
The first-essence step has stayed in my routine through eleven years and four major routine overhauls. The reader I mentioned at the top kept hers. I checked back in March. She had dropped her toner and her ampoule and one of her two serums. The essence was still there.
FAQ
Is first-essence the same as a toner?
No. A traditional Korean toner is a pH-adjusting and hydrating watery step. A first-essence is a ferment- or active-rich watery step designed to deliver small molecules into the partially permeable stratum corneum. Some products combine the two roles. Most do not.
Do I need first-essence if I already use a hydrating toner?
Probably yes, if the toner does not contain a high-concentration ferment. The mechanistic argument is about the ferment-derived small molecules, not just the hydration. If your “toner” is 90% saccharomyces ferment filtrate, you have an essence labelled as a toner and you do not need both.
Will it cause purging?
Fermented filtrates do not have a documented purging mechanism. If you break out after starting one, the more likely culprits are a fragrance, an essential oil, or a humectant your skin does not tolerate. Patch test on the jawline for a week before assuming it is the ferment.
Is SK-II worth the price?
This is the question I refuse to answer cleanly. The marginal benefit over a well-formulated thirty-dollar ferment essence is, in my reading of the literature, small. If you love the texture and the ritual, that is a real value. If you are buying it because you expect proportionally bigger results, the data does not support that expectation.
Can I use it with retinoids and acids?
Yes. The ferment essences are not pH-sensitive in the way niacinamide-plus-vitamin-C debates suggest. Apply the essence first, let it absorb for a minute, then layer your active. The essence may actually buffer some of the sting of a new retinoid.
References
Kim YM, et al. (2014). Effects of fermented Galactomyces filtrate on filaggrin and aquaporin-3 expression. J Microbiol Biotechnol.
Park SH, et al. (2017). Cosmetic effects of fermented yeast extracts on skin hydration and antioxidant activity. J Cosmet Dermatol.
SK-II Pitera research bulletins (1980-present), brand-controlled literature. Read with appropriate skepticism.