How to Use Kérastase Genesis Anti-Hair-Fall Serum (Step by Step)

If you've noticed more hair than usual on your brush, in the shower drain or wrapped around your hairbrush handle, the Kérastase Genesis serum is one of the first things we reach for in the salon. It's a leave-in scalp and lengths serum built around weakened, fall-prone hair, and once people understand how to use Kérastase Genesis serum properly, they tend to keep it in the routine for good. The trouble is most people use it like a regular hair oil, on the ends, occasionally, and then wonder why nothing changed.

So here's exactly how we use it on clients, how much to apply, where it actually goes, and what to honestly expect. These are the products our colourists reach for day to day, not a script off the back of a box.

What the Genesis serum actually does

Genesis is Kérastase's range for hair that feels weakened and prone to falling from brushing and daily handling. The hero serum (you'll see it called Défense Thermique or the Anti Hair-Fall Duo Serum depending on the batch) is designed to sit on the scalp and through the mid-lengths to strengthen the fibre and reduce breakage from styling. The headline benefit is fewer hairs lost to brushing over time, which is a breakage and fragility story rather than a regrowth one. Worth being clear about that up front, because it changes how you judge whether it's working.

If your shedding is sudden, patchy, or tied to a health change, a serum is a supportive step, not a fix. See your GP. For the everyday "my hair feels thinner and weaker than it used to and I'm losing more in the brush" situation, this is squarely what Genesis was made for.

How to use Kérastase Genesis serum, step by step

The serum is a leave-in, so it goes on after washing and stays in. Here's the routine we give clients.

1. Wash and prep the right way

Start clean. The serum works best on a scalp that isn't coated in buildup, so we pair it with the matching Genesis shampoo and conditioner two or three washes a week. Rinse well. The serum needs to reach the scalp, and a heavy product residue gets in the way.

2. Towel-dry to damp, not dripping

Squeeze excess water out with a towel until the hair is damp rather than soaked. Too much water and the serum just slides off and dilutes; bone dry and it won't spread evenly through the lengths.

3. Apply to the scalp first

This is the step people skip. Genesis is a scalp serum as much as a lengths serum. Part the hair into a few sections and apply the serum directly onto the scalp along each part, working across the whole head, not just the front. A pipette-style applicator makes this easy; if yours has a nozzle, go section by section.

4. Massage it in for a minute

Use your fingertips (not nails) to massage the scalp for about a minute. This helps the product absorb and gives the follicles a bit of circulation, which never hurts. It's also the nicest part of the routine, so don't rush it.

5. Pull the rest through the mid-lengths and ends

Whatever's left on your hands, smooth through the mid-lengths down to the ends. This is where the fibre-strengthening, anti-breakage side does its work, protecting the lengths from snapping during brushing and heat styling.

6. Don't rinse, style as normal

Leave it in. Blow-dry or air-dry as you usually would. It layers happily under a heat protectant and your styling products, so it slots into an existing routine rather than replacing it.

How much and how often

Most people use too little. For shoulder-length hair, a few pumps or one full pipette is about right; longer or thicker hair will want a touch more. You want the scalp lightly covered, not soaked. As for frequency, daily gives the best result, especially through the first six to eight weeks, then you can settle into every wash day if daily feels like a lot. Consistency matters far more than the amount. A serum used twice a month does almost nothing.

How long until you see a difference

Be patient and honest with yourself here. Because the benefit is about reducing breakage and fall over time, the realistic window is six to twelve weeks of steady use before you'd reasonably expect to notice less hair in the brush and lengths that feel stronger. A quick tip we give clients: take a photo of your hairbrush or the shower drain now, then again in two months. It's a far more reliable gauge than how you feel day to day, which is easily swayed by lighting and mood.

What to pair it with

The serum does more when the whole routine supports it. A few combinations we actually reach for:

• The full Genesis range — the matching shampoo, conditioner and bain make a genuine difference because they're built for the same weakened-fibre concern. Browse the lot in Kérastase Genesis.
• A scalp routine — if your scalp runs oily or congested, a clarifying step once a week keeps the follicle area clear so the serum can absorb. See our scalp care picks.
• Densifique — if your main concern is hair that simply feels finer and flatter rather than actively falling, the Kérastase Densifique range and our wider fine and flat hair edit may suit you better, or alongside Genesis.
• Heat protection — most breakage is mechanical, so anything that shields the lengths from heat helps. Our leave-in treatments sit nicely over the top.

If you're not sure whether your issue is fall, fineness or breakage from over-processing, the wider Kérastase range covers all three, and you're welcome to message us for a steer.

Honest pros and cons

We'd rather you buy the right thing once. So, the straight version:

What we like: it's genuinely lightweight, doesn't leave hair greasy or limp (a real worry with fine hair), the scalp application is a habit that's easy to keep, and over a couple of months most clients do report less in the brush. It layers under everything without fuss.

Where it falls short: it's a breakage and fall product, not a regrowth treatment, so don't expect new density where hair has genuinely been lost. It needs daily-ish use to earn its keep, which not everyone sticks to. And it's a premium price, so it's worth being sure your concern matches the range before committing.

A quick word on buying genuine Kérastase

Kérastase is a professional brand, and there's a fair bit of grey-market and expired stock floating around online marketplaces. Tired or fake product is a waste of money and won't perform. Crew Stylists is an authorised stockist, so everything we ship is genuine and in date. We're a real working salon, and Genesis is one of the ranges our colourists keep on the shelf because clients come back for it.

Shop Kérastase Genesis at Crew

Ready to give it a proper run? You can order the Genesis serum and the matching shampoo, conditioner and treatments from our online store, with genuine, in-date stock and free shipping anywhere in New Zealand on orders over $99. Browse the full Kérastase Genesis range or our wider edit of leave-in serums, and reach out any time if you'd like help matching a routine to your hair.

Frequently asked questions

Do you leave Kérastase Genesis serum in or rinse it out?

Leave it in. The Genesis serum is a leave-in scalp and lengths treatment. Apply it to damp hair after washing, massage it into the scalp, smooth the rest through the mid-lengths and ends, then style as normal without rinsing.

How often should I use the Genesis serum?

Daily gives the best result, especially through the first six to eight weeks. After that you can drop back to every wash day if daily feels like too much. Consistency matters far more than how much you use, so a little every day beats a lot occasionally.

How long until I see results from Kérastase Genesis?

Because it works by reducing breakage and fall rather than regrowing hair, give it six to twelve weeks of steady use before judging it. Photographing your hairbrush or shower drain now and again in two months is a more reliable gauge than day-to-day feel.

Is the Kérastase Genesis serum good for fine or oily hair?

Yes, it's lightweight and won't leave fine hair greasy or limp, which is the usual worry. If your scalp runs oily, add a clarifying scalp step once a week so the serum can absorb properly. If your main concern is fineness rather than active fall, the Densifique range may suit you better, on its own or alongside Genesis.