Kérastase Genesis Sérum Fortifiant — 90ml
Kérastase Genesis Sérum Fortifiant — 90ml
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Kérastase Genesis Sérum Fortifiant — 90ml
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"The brush is the whole story. It used to be a nest."
I have long, fine, colored hair, which is a combination that basically manufactures breakage. My hair wasn't thinning at the scalp — the strands were snapping somewhere around my collarbone, so I had this halo of short broken pieces and ends that looked chewed. I've used the shampoo and the mask before and this is the piece I was missing, because it stays in. Damp hair after a shower, mid-lengths and ends, two pumps, comb through. About six weeks in the amount coming out in the brush is visibly less, and the broken halo is growing past my shoulders instead of snapping at the same spot.
"It didn't stop the shedding. It stopped the breakage on top of it."
I want to be honest because I looked for an honest review and couldn't find one. Postpartum shedding is hormonal and no serum is going to stop it — mine ran its course on its own schedule. What this did was keep the hair I still had from snapping while it was happening, so the regrowth coming in at my hairline actually got long enough to blend instead of breaking off at two inches. That was the difference between looking like I was losing hair and looking like I was growing it back.
"Bleach damage. This was the cheapest fix that wasn't scissors."
Went platinum, hated the texture, and my ends turned into something that ripped if I looked at it wrong. A stylist told me I could either cut six inches or commit to a leave-in and be patient. This is weightless enough that I use it daily without my hair going greasy, and the mid-lengths stopped shredding when I brush. I still lost two inches eventually, not six.
"Heat plus fine hair is a breakage machine."
I flat iron most days for work and I know that's the problem, and I'm also not going to stop. This goes on damp before I blow dry and the ends are noticeably less crunchy by the end of the week. It's not magic and it doesn't undo heat, it just seems to buy the fiber enough strength that daily styling isn't costing me an inch a month.
"Same serum my stylist sells. I just wasn't buying it at $64 every time."
I've been using Genesis since my colorist put me on it, and the serum is the one I run out of fastest because it's the one you use every wash. Buying two at a time here instead of one at a time at the salon is the entire reason I ordered. Read the packaging note before you buy so you know what's arriving — I did, and it was exactly what they said.
"She noticed it was the European one."
My wife has used Kérastase for years and immediately clocked that the formula listed Aminexil, which she said the American bottles don't. She was happy about it — apparently that's the version she used to buy in Spain. Worth knowing that's what you're getting, because if you were expecting the identical US bottle, it isn't that.
"Enough slip to detangle without a fight."
My breakage happens at takedown, not in the shower. This gives the lengths enough slip that a wide-tooth comb goes through without me hearing that snapping sound, which is the sound of my hair getting shorter. The comb that came with the bundle is genuinely fine, I use it. Ninety millilitres lasts me about ten weeks with thick hair.
"Three weeks did nothing. Eight weeks did something."
I was ready to write this off. Nothing at three weeks, nothing I'd swear to at five. Somewhere around eight the amount of short broken hairs on my shirt after brushing dropped off and I stopped noticing them. If you need a result in a month, buy something else or buy nothing — this is a fiber thing and fiber takes a growth cycle.
"Two pumps. Any more and it's too much."
First week I used way too much and my roots looked wet by lunch. It's a mid-lengths-and-ends product, not a scalp product, and two pumps on damp hair is genuinely the dose. Once I got that right it disappeared into my hair completely. Mentioning it because I almost returned it over my own mistake.
Most 'hair loss' in the shower
is hair that broke, not hair that fell.
Pick a strand out of your brush and look at the end of it. A shed hair has a small white bulb — that's the root, and it means the hair completed its cycle and let go. A broken hair has no bulb; it's a blunt or frayed end, because it snapped somewhere along its length. Most of what people panic about is the second kind — fiber that has been bleached, heated, brushed wet, tied up and weakened until it gives out mid-length. That's a fiber-strength problem, and it's the one a leave-in serum can actually work on. Genesis Sérum Fortifiant uses Aminexil, Ginger Root and Edelweiss on the lengths and ends, where the breaking happens.
Heat And Friction
Along Its Length
No Root On The End
And Call It Hair Loss
Masks work, but they leave with the water. For hair that's breaking between washes — brushing, tying, heat styling, sleeping on it — the protection isn't there when the damage happens. A mask is the treatment; a leave-in is the armour.
Scalp serums target the follicle, which is the right answer for genuine thinning and the wrong answer for snapping. If your strands have blunt ends and no root bulb, follicle stimulation isn't the problem you have — and those are drugs with their own rules.
A weightless leave-in that stays on the mid-lengths and ends all day, where breakage actually occurs. Aminexil, Ginger Root and Edelweiss on damp hair, no rinse, no residue, no flattened roots — used at every wash, which is the only way fiber work adds up.
Two pumps, every wash, no rinse
Damp is the whole trick: wet hair dilutes it and dry hair won't take it evenly. Two pumps is the dose for most people and it is genuinely easy to overdo — start there, and only go to three if you have thick or very long hair. This is not a scalp product.
Start around the level of your ears and work down. The roots don't need it and putting it there is how people end up with hair that looks wet by lunch. Comb it through with a wide-tooth comb so it's distributed evenly rather than concentrated where your hands were.
No rinse. Blow dry, air dry, heat style — it goes underneath all of it. The results people report show up on a hair-growth timescale, not a skincare one: not much at three weeks, something real around eight. Consistency at every wash matters far more than using more per application.
The broken halo vs. this
This serum is for you if…
That's the tell. No bulb means it broke rather than shed, and breakage is a fiber-strength problem you can actually act on. If every strand has a root bulb and your part is widening, you want a scalp or medical route instead — and we'd rather say so than sell you the wrong bottle.
Neither would we. The realistic move isn't quitting heat, it's making the fiber strong enough to survive it. A leave-in is protection that's still there hours later when you're brushing, tying it up, and sleeping on it — which is when most of the damage actually happens.
Long, fine, curly, coarse or in protective styles — if you can hear it breaking as you comb, you need slip and strength at the mid-lengths and ends. That's exactly the zone this product is designed for, and exactly why it's a leave-in rather than a rinse-out.
It's the one you use at every wash, so it's the one that runs out. If your salon has you on the line already, buying two at a time is the only thing that changes here — the formula is the European version with Aminexil, which is detailed in the FAQ below.
Where this fits
| Genesis Sérum Fortifiant | Rinse-Out Mask | Scalp Serum | Drugstore Leave-In | |
|---|---|---|---|---|
| Stays on the hair between washes | ✓ | ✗ | ~ | ✓ |
| Targets breakage along the fiber | ✓ | ✓ | ✗ | ~ |
| Aminexil in the formulation | ✓ | ✗ | ~ | ✗ |
| Weightless — no flattened roots | ✓ | ✗ | ✓ | ~ |
| Enough slip to detangle without snapping | ✓ | ✓ | ✗ | ~ |
| Salon-line concentration | ✓ | ✓ | ~ | ✗ |
| Cost | $54.99 | $40–68 | $25–90 | $8–20 |
Everything you need to know — including the awkward parts
Which version of Genesis is this, exactly?
This is the 90ml Genesis Sérum Fortifiant in the European formulation, which lists Aminexil among its actives. The version sold at US retail does not contain Aminexil — the two products share a name and a bottle design but are not identical formulas. We're telling you this up front because it's the single most common surprise with this product, and because some people specifically want the European one. If you were expecting the exact bottle sold at a US salon, this is not that, and you should not buy it.
How does it arrive? Will it come in a retail box?
It ships in what suppliers call random packing — meaning it may arrive without the printed retail carton, in a plain protective mailer or a generic box. The bottle itself is sealed and unopened. If receiving a giftable retail box matters to you, buy it from a salon or a department store instead, because we can't promise one and we're not going to pretend otherwise. Most returns in this category happen because nobody said this out loud.
How long does delivery take?
Typically 10 to 14 days, because it ships from overseas rather than a US warehouse. That's the honest number, not a best case. If you need it this week, this isn't the right way to buy it. Every order is tracked and covered by the 30-day guarantee below.
Will this regrow hair I've already lost?
No. It's a cosmetic leave-in that works on the strength of the hair fiber, not a medical treatment for hair loss, and it does nothing for follicles that have stopped producing. What it targets is breakage — hair snapping partway along its length, which is what a large share of what people call 'shedding' actually is. If your hairs come out with a small white root bulb attached, or your part is visibly widening, see a dermatologist rather than buying a serum.
How long until I see something?
Longer than you want. Reviewers consistently report nothing meaningful in the first three to four weeks, and a noticeable drop in broken hairs somewhere around eight. That's a hair-growth timescale, not a skincare one, and one 90ml bottle at every wash is roughly eight to twelve weeks of use depending on your length and thickness. If you want a result inside a month, buy something else.
How much do I use, and where?
Two pumps on towel-dried hair, worked through the mid-lengths and ends, then combed through. Not the scalp, not the roots. The most common complaint from people who dislike it is greasy-looking roots, and it's almost always because they used four pumps and started at the top. Start with two and only increase if your hair is very thick or very long.
Can I use it with the rest of the Genesis line?
Yes, and that's how it's designed to be used — bain, then masque or conditioner, then this as the leave-in step on damp hair before styling. It's also perfectly fine on its own over whatever shampoo you already use. Nothing about it requires the rest of the range.
Why is it cheaper here than at a salon or Sephora?
US list is $64.00 and it's held at that price across authorized US sellers. This is $54.99 because it comes through an overseas channel rather than the US distribution chain — which is also why it's the European formula, why it takes 10 to 14 days, and why it may not have a retail box. Those three things are the trade. If any of them bother you, pay the $64 at a salon; that's a completely reasonable choice and you'll get the US bottle in a box tomorrow.
GUARANTEE
30 days, risk-free — including if it's just not what you expected.
Use it for a month. If the texture isn't right, if you don't see a change in what's coming out of your brush, or if the European formula and the plain packaging aren't what you pictured — send it back for a full refund, bottle opened and all. We put the formula difference, the shipping time and the packaging in the FAQ instead of the fine print precisely so that nobody has to find out after the fact.