Fermented herbs in Korean haircare: ginseng, centella, green tea, rice water

Fermentation appears on Korean cosmetic labels the way cold-pressed appears on juice. It sounds like a virtue. It is worth knowing what it does, what it does not, and where the studies actually come from.

Two of the four ingredients below are routinely misrepresented, and both misrepresentations are easy to spot once you know what to look for.

What fermentation does to an extract

Fermenting a plant extract with a bacterial or fungal culture cleaves large molecules into smaller ones. Glycosides lose their sugar groups. Polysaccharides shorten. The practical result is a lower average molecular weight.

That matters because of the 500 Dalton rule, described by Bos and Meinardi: compounds heavier than roughly 500 daltons do not meaningfully cross intact skin. Their evidence was that virtually every common contact allergen and every widely used topical drug falls below the threshold.

Ginseng, and the word nobody reads

The active compounds in Panax ginseng are ginsenosides. Fermentation converts the bulky protopanaxadiol forms into compound K, which absorbs far better. The most-cited human study found that after a single 3 gram dose of fermented red ginseng, blood levels of compound K were roughly 115 times higher than after ordinary red ginseng.

That is a genuinely large number, and it is doing a lot of work in a lot of marketing copy.

Centella asiatica

The best-supported ingredient of the four, though the support is for skin rather than hair. Its triterpenes — asiaticoside, madecassoside, and their aglycones — have reasonable evidence for modulating inflammation, supporting collagen synthesis, and assisting barrier repair, across in vitro and in vivo work.

On a reactive scalp, that is a sensible thing to want. Reviews of the literature are also clear that better-controlled long-term clinical trials are still needed, and none of it speaks to hair density.

Green tea and the in vitro problem

Epigallocatechin-3-gallate, or EGCG, is a well-characterised antioxidant. Kwon and colleagues showed that EGCG promoted the proliferation of cultured human dermal papilla cells and elongated hair follicles in ex vivo culture.

Rice water

The traditional claim rests on inositol. Here I will do something the category does not: I am not going to cite a study, because the evidence is largely historical and anecdotal, and the frequently referenced work concerns hair strand elasticity rather than growth.

What is defensible is that fermented rice water is mildly acidic, which sits near the scalp's own surface pH. That is a real, small benefit. It is not the reason anyone in a photograph has hair to their waist.

The four ingredients, honestly summarised

How to read an ingredient list

• Order matters. Ingredients are listed by descending weight. A botanical listed below the preservative is present in trace amounts.
• “Ferment filtrate” and “ferment lysate” indicate an actually fermented input. “Extract” alone does not.
• A formula advertising 12 botanicals at 0.1 percent each is a marketing decision, not a formulation one.
• Rinse-off products have limited contact time. Judge them on how well they cleanse and on what they avoid irritating, not on their actives.
• If a brand cites a study, check whether the route of administration matches the product. Oral is not topical, and a dish is not a scalp.

So what are fermented botanicals actually good for

They are a reasonable choice for a scalp cleanser. They are gentler than sulfate detergents, they absorb better than their unfermented counterparts, and several of them have real anti-inflammatory data behind them. That is the accurate case, and it is enough to justify buying one.

It is not enough to justify expecting regrowth, and a company that needed to promise regrowth to sell you a cleanser would be telling you something about its cleanser.