I was slightly sceptical about the idea of an overnight serum for hair.

Skincare before bed makes perfect sense to me, but putting a leave in treatment through my hair and then sleeping on it sounded like something that could easily end with greasy lengths and a pillowcase that needed washing the next morning.

Kérastase Nutritive 8H Magic Night Serum turned out to be much lighter than I expected.

It is designed for dry hair and works as an overnight conditioning treatment rather than a traditional hair oil. I apply it through the lengths and ends before bed, leave it in overnight and do not rinse it out the following morning.

The main reason I kept using it was simple. My hair felt softer and looked smoother when I woke up, without feeling as though I had slept with a heavy treatment coating it.

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What the serum actually feels like in my hair

The texture sits somewhere between a lightweight cream and a serum.

It has more body than a hair oil, but it disappears into the lengths surprisingly quickly. I warm it between my hands first and then work it mainly through the middle of my hair and the ends, where I tend to notice dryness most.

I avoid putting it directly onto my roots because that is not where I need the extra conditioning.

The amount you need really depends on your hair. Kérastase suggests roughly two to four pumps depending on thickness, and I think that is a much more useful guide than telling everyone to use exactly the same quantity.

Fine hair needs much less than thick, dry hair. Using far too much simply because it is an overnight treatment is more likely to make the hair feel coated than improve the result.

There is also a noticeable fragrance.

Kérastase haircare tends to smell quite luxurious, and this is no exception. I enjoy the scent, particularly in the evening, but it does linger in the hair for a while. If you strongly dislike fragranced hair products, that is worth knowing before buying it.

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How I use it before bed

I usually apply the serum to dry hair, although it can also be used on damp lengths.

I concentrate it through the mid lengths and ends, then brush or run my fingers through my hair to distribute everything evenly.

That is it.

There is no need for a shower cap, towel or complicated overnight routine, and you do not need to wash the product out in the morning.

That simplicity is probably why I have continued using it. If an overnight treatment required me to protect the bedding, rinse my hair first thing in the morning and then restyle everything, I know I would eventually stop bothering.

With this, I can apply it before bed and carry on as normal the following morning.

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What my hair feels like the next morning

Softness is the most obvious difference for me.

My lengths feel smoother and less rough when I wake up, particularly through the ends where my hair tends to feel driest.

There is also less of that fluffy, slightly frizzy texture that can appear overnight. My hair looks more controlled and feels easier to brush without needing to add a lot of oil immediately afterwards.

Kérastase reports up to 84% less frizz, up to 48% softer hair and up to 40% more shine in its own instrumental testing.

I would not expect everybody to see those exact percentages at home, and I certainly could not measure my own hair in that way.

What I can say is that the difference in softness is noticeable on me.

The result is not dramatic in the sense that damaged hair suddenly becomes completely healthy overnight. It is more that the hair feels better conditioned and easier to manage the next morning.

That is enough for me to see the point of using it.

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Does it make your hair or pillow greasy?

This was the thing I was most concerned about.

I did not want to put a treatment through my hair before bed and wake up feeling as though I had slept in hair oil.

Used in the right amount, I do not find it greasy.

The serum absorbs surprisingly well through the lengths, and I have not found that it leaves an obvious oily coating on my pillow.

The key is not using more than your hair needs.

If your hair is fine and you apply four or five generous pumps simply because the product is meant to work overnight, you may have a very different experience.

I would start with less, concentrate it on the driest areas and add another small amount only if necessary.

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What it can and cannot do for damaged hair

I think this is important because haircare language can make products sound as though they permanently reverse damage.

The 8H Magic Night Serum contains conditioning ingredients including niacinamide, glycerin, panthenol and hydrolysed proteins, along with silicones that help smooth the surface of the hair.

That combination can make dry or damaged lengths feel much softer and look smoother.

It does not glue split ends permanently back together or turn heavily processed hair into untouched hair.

When my ends look rough, the serum makes them feel smoother and less obvious. That is a cosmetic improvement, but it is still a useful one.

If my hair were badly damaged from bleach or excessive heat, I would not rely on this one product alone. I would also look at how I was washing, styling and protecting the hair in the first place.

For me, this works best as an ongoing conditioning step rather than a miracle repair treatment.

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Is it only for very dry hair?

I do not think your hair needs to be extremely dry to benefit from it, but dryness is definitely where it makes the most sense.

My lengths tend to need more help than my roots, so I like being able to target just those areas.

If your hair is naturally very fine or becomes greasy easily, you may find a full overnight serum unnecessary. A tiny amount through the ends may be enough.

Thicker, longer, coloured or heat styled hair probably has the clearest reason to use it regularly.

The biggest mistake would be treating every hair type the same.

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30ml or 90ml?

Kérastase sells the 8H Magic Night Serum in both a smaller 30ml size and the full 90ml bottle.

If you have never used an overnight hair serum before, I think the smaller size makes a lot of sense.

It gives you enough product to decide whether you like the fragrance, whether your hair responds well to it and how much you actually need per application.

If you already know you love it and use it regularly, the 90ml bottle is much better suited to ongoing use.

Because Kérastase is premium haircare, I would compare the live prices rather than automatically buying it at full RRP.

Lookfantastic stocks the serum, and I usually check where I can currently save on Kérastase at Lookfantastic before ordering.

My usual code to try is LFTFNICOLAL, which gives 20% off eligible products when accepted at checkout.

Kérastase can sometimes already be reduced or included in a different retailer promotion, so I always check the basket total before paying.

I also look at the Look Fantastic haircare offers I am currently using if I am buying several products from the range together.

Sephora UK also stocks the 8H Magic Night Serum, so it is worth comparing both. I check the Sephora haircare savings I use for premium brands alongside the live product price before deciding where to order.

For something this expensive, comparing the 30ml and 90ml bottles as well as the retailer offer can make a meaningful difference.

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Is Kérastase 8H Magic Night Serum worth £52?

I do think it is expensive for a leave in hair treatment.

There are plenty of cheaper conditioners, masks and oils that can make dry hair feel softer.

What I like about the Kérastase serum is the convenience.

I do not need to wash it out, it does not turn the hair into an oily mess and it takes seconds to apply before bed. By morning my lengths feel noticeably smoother without creating another job in my routine.

That convenience is what makes it more interesting to me than another deep conditioning mask.

A mask means washing, applying it, waiting and rinsing.

This goes on before bed and stays there.

If you already have soft, healthy hair and rarely struggle with dryness, I would probably spend the money elsewhere.

If your lengths constantly feel rough and you like premium haircare, I can see why this becomes one of those products you keep replacing.

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Can I use Kérastase 8H Magic Night Serum every night?

You can use it regularly, but I do not think everyone needs it every single night.

I use it according to how my hair feels rather than applying it automatically. If my lengths are already soft and smooth, I leave them alone.

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Do I need to wash my hair the next morning?

No. It is a leave in overnight serum and does not need to be rinsed out.

I style my hair normally the following morning.

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Can I use hair oil as well?

Yes, but I would not necessarily apply both heavily at the same time.

I use the Kérastase serum for overnight conditioning and then add a small amount of hair oil later if I want extra shine or smoothing through the ends.

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Kérastase 8H Magic Night Serum sounded slightly unnecessary to me before I tried it.

I already use conditioner, masks and hair oil, so adding something specifically for bedtime felt like another beauty step invented to sell me another bottle.

What changed my mind was how easy it is to use.

The serum sinks into my lengths without leaving them heavily coated, does not need rinsing and makes my hair feel noticeably softer the next morning.

It is particularly good when my ends are feeling dry or my hair has become fluffy and harder to manage.

I would not buy it expecting damaged hair to be permanently repaired overnight, and I do think £52 is a lot of money for 90ml.

But as an easy conditioning treatment that genuinely improves how my hair feels by morning, it has earned a place in my routine.

Final rating: 4.6/5

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Kisses, Nicola xxx

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