Vichy renamed this serum when it crossed the Atlantic, dropping the word 'probiotic' from the label, and the reason for that rename is the most interesting thing about what's in the bottle. In Europe it launched in 2021 as Normaderm Probio-BHA, sold on the pairing of salicylic acid with 'probiotic fractions'. In the US since 2023 it is the Normaderm BHA Exfoliating Serum, salicylic acid registered as an over-the-counter acne drug, and the fifth-highest ingredient by concentration, a 5% lysate of a bacterium called Vitreoscilla filiformis, is mentioned almost in passing. The American label is the more honest one. Nothing in this serum is alive. But the story of that dead bacterium is why this is a more thoughtful acid serum than most.
Start with the acids, because they are what you will feel. Salicylic acid at 1% sits at the low end of the FDA monograph range for an acne active, and glycolic acid at 4% is a gentle daily-use level for an alpha hydroxy acid. Neither number is impressive alone, and that is the point. Vichy has built a two-acid serum meant to be used most nights, and to make that tolerable the individual doses have to be modest. The salicylic acid is oil-soluble, so it goes where the trouble is, into the pore, and loosens the mix of sebum and dead cells that becomes a blackhead. The glycolic acid is water-soluble and works on the surface, thinning the dull, rough top layer and speeding the turnover that fades the flat red and brown marks acne leaves behind. Between them sits HEPES, a biological buffer that is the third ingredient. It holds the pH steady so the acids behave the same on day one and day sixty, and it has a quiet exfoliating action of its own by activating the enzymes that release dead cells. That is the detail that explains why this serum resurfaces more than its percentages would predict.
Now the bacterium. Vitreoscilla filiformis is a harmless, non-pathogenic organism that L'Oréal's researchers have been growing, lysing and putting into creams for two decades, mostly for eczema-prone skin. There is a 2008 randomized, double-blind, placebo-controlled trial in the British Journal of Dermatology in which a 5% lysate cream improved atopic dermatitis scores, itch and barrier function versus vehicle over a month, and a 2022 review in JEADV describing how the extract grown in Vichy's volcanic water increases the skin's own antimicrobial peptides and tight-junction proteins in the lab. The ferment here is at that same 5%. It is not treating acne. It is there because two acids used nightly put stress on the barrier and tilt the skin toward inflammation, and this ingredient has actual clinical evidence, albeit funded by the company that makes it, for pushing back in the other direction. In a category where 'soothing' usually means a trace of allantoin, that is a real distinction.
The experience is less refined than the formulation. The second ingredient is denatured alcohol, and the last is menthol, and together they make the serum feel like a medicinal toner: a sharp mint-and-spirits smell, a distinct cooling sting for the first half minute, a flush on freshly cleansed skin. Alcohol here is doing honest work, thinning the fluid so it spreads and dries invisibly, and helping the salicylic acid dissolve, but it is still alcohol on skin you are also exfoliating. Menthol is doing nothing except telling you the product is working. Oily, resilient, acne-prone skin, the skin this is designed for, tends to shrug all of that off and even like it. Dry, sensitive or rosacea-prone skin will not, and the reviews that call it too strong are almost all from people who should not have been sold it. Fragrance-free, which this is, has been mistaken for gentle, which this is not.
Where it lands well, it lands fast. Blackheads on the nose and chin loosen within a week or two. Skin texture smooths noticeably without visible flaking, which is the HEPES-buffered acids doing their steady work. Active breakouts thin out over about a month, and the flat marks they leave fade over six to eight weeks, helped a little by the ascorbyl glucoside near the end of the list, provided you wear sunscreen, which with 4% glycolic acid in the routine is not optional. A short purge of small whiteheads in the first fortnight is common and is the pores emptying, not the serum failing.
The bottle deserves a mention because it shapes how the serum gets used. Deep green glass, a dropper built into the cap that you fill by turning the bottle over and squeezing the bulb, three or four drops per application. It meters neatly and keeps the acids away from light, and it also makes the last few millilitres annoying to extract. Thirty millilitres at three to four drops a night is a two-to-three-month supply, which brings us to the price.
Forty-five dollars for 30 ml is prestige-adjacent money for a pharmacy brand, and it is the weakest part of the proposition. You are paying for a well-buffered two-acid system, a ferment with real trial data, French manufacturing and the Vichy name, and there is no larger size to soften the per-millilitre cost. Dermstore's subscription price knocks it down somewhat, and the serum does go on sale, but at full retail this asks more than most daily exfoliants. Whether that is fair depends on how much you value the barrier-support science; the acids themselves can be had for far less.
Vichy has been making skincare around its thermal spring since 1931 and has had L'Oréal's research division behind it for seventy years, so this is not a brand that needs the benefit of the doubt on formulation competence or safety testing. What this serum shows is that competence used well: sensible acid doses, a clever buffer, and a soothing ingredient chosen because someone ran a trial on it rather than because it sounded nice. It is undermined by a sensory base that limits who can use it and a price that limits who will. For oily, congested, mark-prone skin that can handle a bit of alcohol and likes to feel a product working, it is one of the better nightly exfoliants at the pharmacy counter. For everyone else, the tingle is the warning.
