Why I Think K18’s Leave-in Molecular Repair Mask Isn’t for Everyone
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Healthier hair in four minutes? That’s what K18’s Leave-in Molecular Repair Mask (£70 from Cult Beauty UK /$75 from K18 US for 50 ml) promises, supposedly “reversing hair damage” with every wash. And thousands on socials seem to agree.
As someone who’s been paying a lot more attention to my hair recently, I was intrigued.
My own very long (it literally touches my bum) hair has been bleached in the past (hairdressers have told me it must be made of steel with the sheer volume of different colours I’ve dyed it) and I’d generally neglected it for far too long.
That was until after years of dyeing and heat styling, I started looking after my hair more around three years ago – ditching the heat and colouring in the process. Since then, my hair has become a lot wavier into the curly/wavy girl method.
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The only issue is that the ends of my hair, despite regular trims, can still be fluffy and look dry and damaged. Especially on day two or three after washing, when my waves start to drop and it just looks sort of kinky.
That’s why, after seeing hundreds of glittering reviews of K18’s leave-in mask online- with some people claiming this conditioner even changed or transformed their dry and damaged hair– I found myself fully influenced in trying it.
Scroll on to see whether it managed to live up to its hype – or just ended up abandoned on my bathroom shelf.
AT A GLANCE
- Best for: Bleached, heat-damaged or heavily processed hair.
- Not ideal for: Relatively healthy hair or anyone wanting to preserve natural waves.
- Key technology: K18PEPTIDE™, which the brand says reconnects damaged polypeptide chains.
- K18 vs Olaplex: K18 is quicker and more nourishing to use, but Olaplex No. 3 is considerably cheaper.
- Our verdict: Noticeably smoother, shinier hair, but the high price and loss of wave definition made K18 difficult to justify for our reviewer’s relatively healthy hair.
- Our rating: 3.5/5
K18 Leave-In Molecular Repair Hair Mask ingredients and claims
This brand has a full range, including their damage shield pH protective shampoo, damage shield protective conditioner, molecular repair hair oil, as well as the leave-in mask itself.
I bought the smaller travel size of this mask (£30 from Cult Beauty UK /$29 from K18 US for 15ml) because I’d like to see how it works on my hair and how it fits into my curly girl method before I invest in the very expensive full size.
K18 is a reparative leave-in treatment that targets the inner polypeptide chains instead of the cortex, where the disulphide bond repair products work.
According to the brand, “This patented bioactive peptide treatment strengthens and improves elasticity while reversing damage from chemical services, thermal styling, and mechanical styling.”
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It’s suitable for all hair types and will help to repair hair that’s been damaged through “bleach and colour, heat, chemical services, and mechanical styling”.
It’s “clinically proven to reverse damage in just 4 minutes” and claims to restore damaged hair, replacing it with hair that’s softer, smoother, and has more bounce. It also promises to reduce breakage and split ends (you can’t actually repair split ends, but you can prevent them), restore the original strength of the hair, and improve elasticity. And you’ll apparently start seeing results within two to three uses of the mask.
How I Tested K18’s hair mask
Since I don’t have particularly dry or damaged hair, I didn’t use my K18 mask the six to eight consecutive washes the brand recommends as an initial treatment course. Instead, I used this twice on freshly washed hair to see whether I did notice any positive effects on my largely healthy hair.
As instructed by the brand, each time I shampooed my hair before towel drying it until it was damp. I then sectioned my hair and applied a few pumps of the product with my hands. I then waited four minutes before brushing and applying further product to bring out my natural waves.
Common misconceptions with this mask are that you need to wash it out or that you can brush it through hair before the four minutes are up so I resisted doing both of these, which felt strange to me since I don’t normally use leave-in conditioners or masks.
My first impressions
So 15ml isn’t very big for someone who has a lot of hair that’s very long. But, the brand says you only need a few pumps to cover the strands – more on this later.
The product looks fine – a small, white circular bottle with black text. Nothing exciting, but it’s what’s inside the bottle that counts! I added a few pumps to the back of my hand to check out the texture and smell, which is a very light floral scent with notes of peony and jasmine. It’s a nice fragrance that isn’t too overpowering.
The texture is quite thin and creamy, I’ve got a feeling I’m going to have to use a lot more than a few pumps for my hair. Because the brand says this is good for all hair types – including wavy, curly, and coily – I was hopeful that this could be a great addition to my curly girl routine.
I checked out a few reviews from curly-haired guys and gals, which reassured me that this wouldn’t mess up my usual haircare routine.
I carried on as usual then, first using my wavy hair shampoo and conditioner, before brushing the conditioner through, rinsing, then applying curl-activating products. Afterwards, I ‘plop’ my waves with a microfibre towel for around 15 minutes – 30 minutes.
Applying it to my hair
Wavy hair needs plenty of nourishment and moisture to help the waves form and keep them in shape, so skipping conditioner feels slightly strange. K18 says not to use a conditioner after shampooing because it deposits “a film that blocks our peptide from penetrating effectively.”
As I suspected, I needed around 10 pumps of the mask to cover my hair. However, this is the smaller travel size so keep in mind that it doesn’t dispense as much product as the larger size.
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I washed my hair and thoroughly towel-dried it until it was slightly damp (this is important). I started with five pumps (which are very small) but this only covered half of my hair so I added another five and smoothed it all over the strands, making sure it covered the tips. This amount of pumps gave me the same amount of product as a few pumps of the full-size bottle.
The brand says to make sure to not use too much of the product, so I kept this in mind, too.
I waited four minutes as instructed, then brushed the product through my hair. My hair can be quite hard to brush once it’s damp, and I sadly didn’t notice that this was any easier with the mask on.
My K18 hair mask results
I then applied a curl-activating gel, a leave-in curl-holding spray, and a tiny bit of argon oil hair serum that I warmed in my hands first. I use the ‘squish’ and pulse method for wavy hair, using a microfibre towel which I then use to ‘plop’ my hair for the next 15 – 30 minutes to promote the waves and help them to hold.
I can’t help but think I might have had better results if I had used a leave-in conditioner after the K18 mask, however, I don’t normally use one and I didn’t want to put too many products in my hair that could make is greasy or crunchy.
My hair wasn’t easier to brush, but as it dried it did look slightly shinier and the ends weren’t fluffy at all. After my hair had fully dried, my waves looked slightly smoother than normal and it seemed to help my waves find their ‘partner strands’ to create a better shape.
Before using the mask, while my hair was drying, and the next day. Image – Live That Glow
The downside is that my hair was significantly less wavy using this mask. It didn’t encourage my natural texture at all, and I’m pretty happy with the products I currently use. My hair isn’t particularly damaged, so this could be a more suitable mask for those who have extremely heat or chemical-damaged strands.
I also felt that my hair looked a bit greasy and stringy the day after using K18’s mask, but again – I suspect I’m not K18’s target customer. As I mentioned, I’m not prone to dryness or split ends, and my main concern is enhancing my natural texture.
A quick poll of the LTG office though tells me that my colleagues with genuinely dry, damaged hair are major fans. My editor, Sally, is now on her second bottle (full size) since it’s done so much to rescue her highlighted and heat-styled wavy hair. In fact, she tells me she significantly prefers this to the results she ever had with Olaplex No 3. Speaking of which…
How K18 compares to Olaplex No 3
A similar product is Olaplex’s No 3 Hair Perfector (£32 from Cult Beauty UK /$34 from Sephora US). Both No 3 and K18’s Repair Mask are bond builders that aim to repair the internal structure of hair.
Olaplex No 3 does this by using an ingredient called Bis-aminopropyl Diglycol Dimaleate to repair hair’s broken disulfide bonds (the bonds which keep the keratin in hair together), while K18 uses an ingredient called sh-Oligopeptide-78 K18PEPTIDE (a type of peptide that they claim mimics hair’s structure) to reach the innermost part of our hair, the polypeptide chains.
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K18 claim that their product therefore goes further to repair damage than other bond builders like Olaplex.
I’ve also used both and I find that while Olaplex does have a very slight effect on reducing signs of damage on my hair, it’s not at all moisturising so you really do need a separate conditioner when using this product. In comparison, K18 kind of does it all- repair and nourish- in one product.
What other users are saying
There are plenty of positive reviews for this mask, with lots of people saying it’s transformed and repaired their damaged hair. There’s also lots of discussion on how to use the product because there does seem to be some confusion – I’ve even seen people say that you should apply the product onto your hands and rub them together to emulsify it to get the best results. This isn’t something that’s stated on the K18 website so I’d avoid.
So many people are comparing this product to others like Olaplex No 3 too, with one user on Reddit claiming that K18 is much better for their hair than Olaplex, “I think it’s amazing. The result is much more dramatic than olaplex for me. I have bleached hair and the k18 makes it feel like normal healthy hair, especially over time with consistent use.”
However, some people still swear by the Olaplex No 3, with one user saying, “I use both Olaplex 3 and K18 at home (not at the same time), but I feel my hair looks and feels better after the Olaplex. After using the K18 my hair feels heavy and flat, and looks greasy after in less than 24 hr.”
Overall value for money
I haven’t used this consecutively over five to six washes like the brand advises, however, I was interested to see whether this mask really could make a difference in just one or two uses.
I can’t say I will ever spend £70 on a hair product. Possibly if I want to treat myself or if I come into some spare cash, but I can think of much better ways to spend that amount of money (sorry!)
I would possibly purchase the travel size again for a shot of hair repair, and I’d imagine I’ll get around four to five washes out of the smaller size (which is still pretty expensive).
As I mentioned earlier, a lot of people compare this to Olaplex’s No 3 Perfect Hair, which is much cheaper.
@anna.ev.pothier Did Coco & Eve just dupe K18?! They’re using their bond repair peptide!! #k18 #dupe #dupes #haircare #bondrepair #thisisthis
Interestingly, during my scrolling on TikTok looking at dupes (this is quite a regular thing for me since I love affordable brands), one influencer says the Coco & Eve Hair Repairing Leave-in Treatment (£28 from Coco & Eve UK /$34 from Ulta US) contains bond repairing peptides and does a very similar job. And it’s cheaper.
The takeaway
Overall, my hair is slightly shinier and smoother, but I prefer my current conditioner and haircare routine.
Since my hair isn’t very damaged and I’ve been looking after it well over the past few years, omitting heat and mechanical styling and steering clear of chemicals and dyes, I think this product is too heavy for my hair.
Again though, I just don’t think I’m the target audience here and so I reckon this could be a great product for very dry and damaged hair – which could make the price a little easier to swallow, too.
