Count the hyaluronic acids on this label and the number lands at seven: sodium hyaluronate, hyaluronic acid, hydrolysed hyaluronic acid, hydroxypropyltrimonium hyaluronate, potassium hyaluronate, a crosspolymer and sodium acetylated hyaluronate. Bioheal BOH rounds the figure up to ten on its packaging by folding in its own trademarked 'Hyalcell' complex, and the serum is built around the idea that a spread of molecular sizes and charges gives a more even, longer-lasting hydration than one grade of HA alone. It is a real formulation principle, not a gimmick, although it is worth knowing where those seven actually sit before paying for the idea.
They sit in the middle of the list, after the pH adjuster, the preservative booster and a small cooling agent. That is not unusual. Hyaluronic acid is a high-performing molecule at low concentration, and most serums built on it use well under one percent because more turns sticky. The heavy lifting in terms of volume comes from above: dipropylene glycol, butylene glycol, glycerin, propanediol, xylitol, betaine, erythritol and trehalose. This is a stacked humectant base, the kind Korean formulators do very well, and it is the reason the serum feels hydrating the instant it hits skin. The HA grades then decide how that hydration behaves over the next few hours: large chains film the surface and reduce evaporation, smaller hydrolysed fragments sit more comfortably in the upper layers, and the cationic hydroxypropyltrimonium form clings to skin rather than rinsing off with the next step.
Bioheal BOH is Olive Young's own skincare label, and the Hyalcell range, a serum and cream launched together in mid-2024, was its answer to the hydration category that the retailer's shelves already crowd with competitors. The serum is the lighter half, labelled for dry and combination skin. It is housed in a translucent blue dropper bottle that looks, fittingly, like a glass of water, and the texture follows: a clear, slightly bouncy gel-water that spreads thin and turns tacky for about a minute before settling to a soft, invisible finish.
That minute of tack is where the cooling agent shows up. Menthoxypropanediol, a menthol derivative that stimulates cold receptors more gently than menthol itself, gives a faint chill on application. Paired with eucommia bark extract, the brand markets this as 'cooling down heated skin'. The sensation is pleasant in summer and after sun, and most skin will not notice it beyond a whisper. The occasional very reactive face may feel a tingle, which is worth flagging for anyone who struggles with even mild menthol derivatives.
Below the HA cluster the formula gets more interesting than a pure hydrator. Ectoin, an extremolyte produced by bacteria that survive salt lakes and deserts, has a small but steady body of evidence for reducing water loss and protecting skin cells against stress. Ceramide NP and beta-sitosterol add a touch of barrier lipid, carried by phosphatidylcholine. Panthenol and allantoin round out a gentle, soothing group. Glyceryl glucoside, the sugar-derived humectant that some research links to better water movement in skin, gets named on the carton as the third pillar of the Hyalcell idea. All of this is sensible supporting cast; none of it is at a dose where it transforms the product into a barrier repair serum. The ceramide, in particular, sits too far down to be the reason to buy.
What is missing matters too. There is no fragrance, no essential oil, no drying alcohol and no exfoliating acid. There are no silicones and no plant oils. For a hydrating serum meant to slide under anything, that is exactly right, and it makes the serum easy to layer beneath retinoids, vitamin C or acne treatments that tend to leave skin dry and tight.
In use, the serum is best on damp skin, where the humectant base can hold onto water that is already there. Two or three drops cover the face. On dry skin in low humidity, humectant-heavy serums can feel slightly tight once they have dried down if nothing is layered over them, and this one is no exception; a moisturiser on top makes a noticeable difference. Oily skin can use it alone in summer. Plumpness, the slightly pillowy look of well-hydrated skin, is visible within minutes and fades over the day, which is the honest ceiling for any hydrating serum. Nothing here will change wrinkles or pores, and the brand does not really claim that.
The larger problem is getting hold of it. The serum has vanished from Olive Young's global store and is out of stock at YesStyle, leaving US buyers dependent on independent K-beauty resellers that list it at around thirty-two to thirty-eight dollars for fifty millilitres. That is well above its Korean shelf price and far above what the ingredient deck justifies. There is nothing wrong with the formula for the money, but there is nothing in it that a reader could not find in a well-built hydrating serum for less.
The fair summary is that this is a competent, fragrance-free multi-weight hyaluronic serum with a welcome dose of ectoin and a cooling twist, from a brand with strong domestic sales but only a few years of history. It does its job cleanly and gently. Its reputation outside Korea is thin, with only a handful of reviews visible in English, and its availability is patchy enough that anyone who finds it at a fair price should think of it as a pleasant option rather than a destination.
