What is K18 Leave-In Molecular Repair Hair Mask?

A leave-in molecular repair hair mask from K18, designed to help repair damaged hair bonds and strengthen strands after bleaching, coloring or heat styling.

Is K18 Leave-In Molecular Repair Hair Mask worth it?

Mostly yes. 13 of the 16 gurus who reviewed it give it their stamp of approval, for a Guru Score of 81%.

What is K18 Leave-In Molecular Repair Hair Mask's Guru Score?

K18 Leave-In Molecular Repair Hair Mask holds a Guru Score of 81%. That is our read on how warmly the experts talk about it, based on the verdicts of 16 expert reviewers we have collected. At least one expert has named it a Top Pick in its category.

K18 Leave-In Molecular Repair Hair Mask: a Guru Score of 81%

What the gurus are saying.

Every take we've logged from this product's reviews across YouTube. Click any row to watch the moment they said it.

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Skin Obsessed Mary

33k subs

✓Yay

"I am one hundred percent dedicated to the bond repair mask. It's always in my shower, I use it generally three times a month, and I've been doing so for years and years and years and years."

All 6 takes from Skin Obsessed Mary

⭐️ Products I Can’t Stop Rebuying

"Another bond repair treatment I use regularly is K18. I actually discovered this before a prey and it really started my journey back to soft hair. Now, this is a bit trickier to use. It likes towel dried hair, which then has to be rinsed off. So, for me, it's only once or twice a month, but I keep buying it and I was super excited when they launched this big guy so I don't have to repurchase the smaller ones as frequently."

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"K18 if you haven't used it in the shower it's just an amazing Bond repair product"

⭐️ Spring Beauty Empties

"I love this and I specifically use this right after I get my hair colored. I will use this for three or four showers and it's a bond repair program. I prefer this to [Olaplex]. I stopped using [Olaplex] and I use this instead. I think it's fabulous. [...] What I tend to do is I shampoo my hair, you do not condition it first, you shampoo and then you put this mask in and you leave it in for four minutes."

❤️ Beauty Empties | Will I Repurchase or Not?

"Another fantastic Bond repair product is the K18 Leave-In Molecular Repair Hair Mask. I've been using this even longer than the appre and I actually find that using them together it's the perfect pairing they repair Bonds in different ways. One is pre-shower and then the K18 I use during the shower and I love them both."

🛍️ Summer Beauty Empties | Will I Repurchase?

"The K18 Leave-In Molecular Repair Hair Mask is another little miracle worker that repairs hair bonds. It's another one I've never without, automatic repurchase. I use it in the shower, and when it comes to pairing these items, I use the other product before I get in the shower and then I use the K18 in the shower. It may be high maintenance but my hair thanks me and I don't care."

I Didn't Expect This Much New Beauty

"I am one hundred percent dedicated to the bond repair mask. It's always in my shower, I use it generally three times a month, and I've been doing so for years and years and years and years."

Dr. Jenny Liu

324k subs

✓Yay

"I will add in probably you know in that routine like once a week a bond repair treatment like K18 or something like that."

Top Pick: peptide bond repair treatment

All 8 takes from Dr. Jenny Liu

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"I will add in probably you know in that routine like once a week a bond repair treatment like K18 or something like that."

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"But this is literally the peptide bond repair treatment that has turned my hair around. I really love the science. It's got this unique peptide that penetrates your hair, and you can use it different ways. Before, I would use it as a leave-in mask after shampooing -- I don't condition -- then come out of the shower, apply this, wait 4 minutes, and follow it with my styling products."

Sephora Savings Event 2023 Dermatologist Top Picks | Dr Jenny Liu

"Compared to other hair repair treatments, I personally have had the most noticeable improvement in my hair when I use this consistently. You can use it like once a week or a couple of times a week. It's certainly pricey, but it's a great one to buy during savings events. It's a really rich, dense hair mask that is not overloaded with protein, which I appreciate because some individuals are protein sensitive and a lot of protein can build up and weigh down your hair."

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"This set contains their popular K18 Leave-In Molecular Repair Hair Mask along with the miniature hair oil, and basically both products contain their signature K18 peptide that's been shown to really get into the hair to help temporarily strengthen and repair hair, and over time actually has been shown to really make that more permanent change to helping reduce hair breakage."

Hair Cycling Routine according to a dermatologist | Dr. Jenny Liu

"This K18 treatment is really one of the best things I've done for my hair when it comes to bond repair treatment. It really has turned my hair around from all the coloring and chemical processing and heat styling. [...] You can use it once a week, but in the beginning you can definitely use it more consecutively, like up to four times, to really get that good result."

Dermatologist’s tips on How to minimize hair breakage | Dr. Jenny Liu

"K18 Leave-In Molecular Repair Hair Mask is one of the key products that have transformed my hair. [...] I use this quite a bit in 2023 and throughout 2024 and I do feel like ever since I started using it I have noticed a significant difference in the overall quality and health of my hair. [...] The reason why I love this is because it's worked really well and really it's the convenience of use that's probably really why I've used it so much."

Holiday Gift Set Ideas | Dr Jenny Liu

"K18 is one of my favorite hair repair brands and this leave-in mask really hands down has transformed my hair it is one of my favorite bond repair products. This would be great for anyone that has like dry damaged hair, anyone that like me colors their hair frequently or styles their hair frequently and is looking to do some really effective repair. This comes in a 15 mil hair mask that really has their proprietary K18 peptides."

Dermatologist updated Haircare routine | Dr. Jenny Liu

"K18 Leave-In Molecular Repair Hair Mask I've been using for the past two years now and it has made the biggest difference for my hair and the structural component of my hair. This is a leave-in conditioner so what you do is you wash your hair shampoo your hair and then you apply this mask from root to the end and then after 4 minutes you can apply or style your hair as usual. You can use this on a daily basis like four times a week until your hair gets to a good point and then use it as needed."

Sincerely Miss Ash

195k subs

✓Yay

"This is a must in my hair care routine. It really helps to strengthen and repair the bonds of your hair. Because I'm blonde, I feel like this is a must for me personally. [...] If my hair appointment is coming up, I will use this about two times before my hair appointment just to strengthen my hair. And then post hair appointment, I will use this six hair washes post hair treatment to really strengthen and repair my hair from getting my hair highlighted."

All 7 takes from Sincerely Miss Ash

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"I've been using this now for pretty much two years, and this is the one product that has honestly transformed my hair. [...] It has brought the health back, it makes the ends of my hair a lot stronger, and it does a really good job to repair damaged hair as well. I usually use this as maintenance throughout the month. I don't use it every time I wash my hair, but if I have a hair appointment coming up, I will be consistent with it for the first two to three washes before my appointment."

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"This will truly transform your hair. I have been very consistent with this over the last year, year and a half, and I have truly seen a big difference with my hair. I have been through the ringer with my hair. I've dealt with a lot of breakage and dryness several years ago, and my hair is starting to look and feel so much better. And I really do feel like the K18 brand has really made my hair become the way it looks now. Especially this product right here."

BEAUTY PRODUCT'S I'VE USED UP || SKINCARE, MAKEUP AND HAIRCARE - BEAUTY EMPTIES 2024

"This is the K18 Leave-In Molecular Repair Hair Mask. This really does work to repair damaged hair and to repair the bonds of your hair. I like to use this sometimes several hair washes in a row and then I might take a break for a few weeks and then start back up again. This is a great product to use even after your hair appointment just to strengthen your ends, especially if you've noticed that you have a little bit of damage or maybe your hair's feeling a little dry."

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"Since being really consistent with K18, honestly, this has really improved my hair. And then after the six hair washes, I'll take a break for a while. And then just before I go back to the hair salon again, I will use this one or two times just to strengthen my hair up again. [...] This really is gamechanging whether you have blonde hair or not. This can really improve the bonds and I love it. Every time there's a sale, I always stock up."

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"This is a must-have. This is a product that actually works. That is worth the money. This is a product that will help to repair damaged hair. It helps to strengthen the bonds of your hair and it also helps to add shine and keeping your hair looking as healthy as possible."

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"I will use this once or twice before I go and get my hair done. And by doing that, I have noticed a really big difference with my hair. I have pretty fine hair, so I need to be careful when coloring it, when heat styling my hair, and this has made a huge difference. So, this is a non-negotiable. This always needs to be in my collection."

Dr. Aleksandra Brown

151k subs

✓Yay

"For bond repair, I love the K18 Leave-In Molecular Repair Hair Mask. This is not your typical deep conditioner. It's a biomimetic hair treatment that repairs broken hair chains at a molecular level and restores the strength and elasticity. It works in just 4 minutes to help reverse the damage from bleaching, coloring, heat, or any chemical treatments. Unlike traditional bonding treatments, K18 permanently reconnects keratin chains for lasting damage repair."

Top Pick: bond repair

All 2 takes from Dr. Aleksandra Brown

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"The K18 Leave-In Molecular Repair Hair Mask is my first recommendation in the hair care category. [...] It can be pricey and comes in a tiny package, but it lasts a very long time. [...] This is not your typical deep conditioner. It's a biomimetic hair treatment that repairs broken keratin chains at a molecular level, therefore restoring strength and elasticity. It works in just 4 minutes to reverse that damage for any bleaching, coloring, heat, or any chemical treatments you may have done."

No BS Beauty

89k subs

✓Yay

"The K18 molecular hair mask, [...] you just use a little bit. [...] In the shower, wash your hair, don't apply conditioner, and then when you get out of the shower, I'll just apply a dime-size amount, rub my hands together, and then just apply it to the very ends of my hair, and it does a nice job. This is more for color-treated hair, permed hair, damaged hair."

All 4 takes from No BS Beauty

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"It's the K18 hair mask, it's really nice. It's expensive, but literally I've been working on this bottle for probably a year now. So it would be repurchased if I used a ton of it at a time, which I don't. It's very nice and I like to use a good clarifying shampoo before this because I feel like it soaks in more and works better. So it's just a leave-in product, so you rinse with shampoo, don't apply conditioner, and then apply this."

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"This stuff is expensive. It's 75 bucks, but I will say it lasted the last bottle last me about two years, and I just use it once a week. I'll shampoo my hair, don't put conditioner in it. When I get out of the bathtub, I'll put like a half a pump on my hand and just smooth it into my hair. [...] It's just a leave-in treatment for bleached, colored, permed, or treated hair. Don't want to use it too much."

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"I mean it does last a long time because you use such a small amount, but 101 dollars for a hair mask, I mean it's a good thing it's a good product, but there's no way I could ever justify a hundred one dollars for a hair mask. I mean the ingredients in here aren't like anything. I mean sure they had to do research and development things like that, but something just in there in my gut thing makes me think there's something else going on there."

Doctor Anne

56k subs

✓Yay

"The K18 Leave-In Molecular Repair Hair Mask is one I picked up about two years ago and I feel it helped my hair get even better. I've since sized up to the full size and use it during the week, since you don't condition beforehand, you just apply it and let it sink in. After 10 minutes I go in with some hair oil to detangle and nourish, which saves me time in the wash process over the week. I like it and have already repurchased."

All 4 takes from Doctor Anne

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"I use the K18 Leave-In Molecular Repair Hair Mask that one only on the lengths after washing. Other than that, before bed and before I brush my hair."

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"Despite the high price, I will repurchase it. I think it's a worthwhile investment for anyone with damaged, bleached, or chemically treated hair, particularly if you're dealing with thinning or breakage, and for those with very fine hair it's lightweight enough that it won't weigh your hair down. However, if your hair is already in great condition, you might not see dramatic results that justify the cost."

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"The k18 Leave-In Molecular Repair Hair Mask is a new discovery from 2024. I [...] use it in addition to [...] the Olaplex No 3 Hair Perfector, [...] on alternating washes. Olaplex has more of an immediate effect while K18 seems to have really improved the health of my lengths."

Alexandra Anele

1.45M subs

✓Yay

"K18 Leave-In Molecular Repair Hair Mask, so good. I honestly I just recently started using it, like actually using it, and it is really really good."

Gothamista

683k subs

✓Yay

"A very obvious favorite is K18 Leave-In Molecular Repair Hair Mask. Even though this is creamy, it has a really lightweight texture, at least for my hair. Right after washing my hair, I apply it to my wet strands, and my hair just dries a lot nicer, a lot less frizzy or frazzled. This is advanced hair repair technology that I think works really well in combination with bond technology; it also works from inside out but goes even deeper into the hair to help with repair."

Dr. Shereene Idriss

1.73M subs

✓Yay

"I use this after I shower and it is formulated with SH oligopeptide 78 to help stimulate hair follicle activity and promote healthier scalps. I put it on my hair literally from here down after the shower a tiny drop goes a very long way and it's been working pretty well for me."

Hyram

4.33M subs

✓Yay

"That is a really good price for kerville I mean that's like what 70% markdown crazy I'm kind of Blown Away that they can have prices this low"

Beyond50Skin

32k subs

✓Nay

"I've also started using a bond repair. I didn't have great luck last year with the K18 bond repair."

Dr. Vanita Rattan

1.23M subs

✓Nay

"They have got conditioning agents, it has got hydrolyzed wheat which does help to repair protein, but you have to look at preventing first. You don't want to make the situation worse and then try and cover it up with other good ingredients. This formula just doesn't make any sense to me. I think what they were trying to do is almost give that quick dry feeling to the hair to make you feel like the ingredients have penetrated into the shaft, but it's a mistake."

Kelly Driscoll

91k subs

✓Yay

"I've had good results putting the K18 Leave-In Molecular Repair Hair Mask on my damp hair out of the shower. This is technically against how K18 says to use it, but this is just what works for me in my routine."

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All 4 takes from Kelly Driscoll

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"It's a similar concept to [Olaplex]. I think it really helps to strengthen my hair and helps to keep it in really good shape. I think it helps to resist some split ends and damage on my hair as well in between trims. It's really expensive, it's retailing $75. That is not what it retailed back in 2022, it was still pretty pricey, I think it was pushing maybe $60, which is still I think too much. They raised the price recently. I don't really understand why this is so freaking expensive."

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"I've been using this for a few years and just over the last year, year and a half, I've been using this almost exclusively. [...] After washing my hair and conditioning my hair, I will use this as a leave-on treatment. I use one pump for all of this hair, [...] work it on my ends and then through the mids. [...] You just leave it in. It is a reparative strengthening bonding hair product and it does work very very nicely."

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"I used the K18 Leave-In Molecular Repair Hair Mask right after washing my hair and before blow drying it. [...] I slept on this hair, washed it last night dried it and slept on it, and there's still some nice volume at the roots. I like how this lasts."

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Dr Dray

2.69M subs

✓Yay

"You could also try using a bond repair product. I have personally had good success with that popular K18 hair mask. These just help to re-approximate temporarily the bonds in the hair, especially if you have color treated hair with a lot of damage that ends up getting frizzy in humidity, [...] or excessive heat damage on the hair. [...] The K18 hair mask is not heat activated, unlike the other options."

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"So, I decided to try their molecular repair hair mask. And it really just made a huge difference for me at that time. In particular, it contains a peptide that helps to reapproximate damaged bonds from heat styling, color treatments. It works not only across the hair strand, but down the length as well. So, it helps improve smoothness, shine, manageability. The way you use this kind of trips people up. You use it after you shampoo the hair, but you do not want to condition."

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"The K18 Leave-In Molecular Repair Hair Mask is one of my favorite bond repair products. It works by having an actual mechanism within the ingredients that helps to temporarily reapproximate damaged bonds in the hair. [...] I put this one through the test, and [...] this product works. It does what it says it's going to do. Not only does it work, it works well."

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"I love the K18 Leave-In Molecular Repair Hair Mask. It works to reapproximate the disulfide bonds to help cut down on frizz, brittleness, breakage. If you have damaged ends from doing a lot of heat styling, it's great. I mean, it really works."

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"This product really works. What it does is it helps to reapproximate bonds in the hair. It works along the length of the hair and along the width of the hair. And what that does is help to mend damaged hair from heat styling, dyes, chemical processing, and it really works. The [...] way to use it is you shampoo your hair like you normally would. Then you do not want to put on conditioner."

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Dr. Sam Ellis

898k subs

✓Yay

"Having a bond builder in my routine to help restore those bonds and re-strengthen my hair has been a game-changer. [...] I do K18 about once a month, [...] except after I get my hair bleached, when I [...] will do four rounds of it, using it with every hair wash for four rounds before going back to once-a-month use."

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All 8 takes from Dr. Sam Ellis

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"But then I tried K18 and I was like, 'Oh, my hair could have been doing so much better this entire time because when it repaired those keratin chains, the first thing I noticed is that my hair texture came back.' My natural hair texture is sort of like wavy and it's a pretty nice wave. But after years of bleaching and styling, my hair texture was sort of this flat frizzy. It just was very unappealing. So when I use my K18, I see my hair texture return."

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"I think a lot of people are familiar with the K18 Leave-In Molecular Repair Hair Mask. And this uses a patented K18 peptide, also known as SH oligopeptide 78, to repair the hair. That peptide actually mimics the natural keratin structure of hair and can enter the hair cortex and repair those broken keratin connections. And the beauty of this is it's not just a temporary fix. This can offer a permanent solution in terms of repairing the hair strand."

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"One of my all-time favorites and nothing has really surpassed this yet is by K18, their leave-in molecular repair mask is so so good and when I use that consistently I truly see a difference in my hair. [...] My hair is long, it is bleached, I heat style it all the time, so if it is not looking good or if it is looking good it's pretty obvious."

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"K18 is really kind of my go-to. It is a peptide treatment that is meant to penetrate into the hair shaft to help repair damaged bonds. Within your hair shafts you have thousands, millions of keratin protein and those keratin proteins can get damaged and they can become unstructured in a way where it makes the hair look dry and frizzy and prone to breakage."

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"The K18 Bond repair treatment is kind of my holy grail for many many years. I'm a huge fan of that product."

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"The K18 Hair Repair Mask [...] uses a keratin protein to help restore the keratin protein in your own hair. I've had so many of you message me about this and been totally in love with it. These are types of investments that tend to be more expensive than shampoos or conditioners, but they have been proven to improve the hair structure, so it may be worthwhile if your hair is damaged or you feel like you could optimize your hair a little more."

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"This product uses their proprietary K18 peptide to help repair the hair. Hair repair systems and hair repair technology don't work for everyone but for people who they work for they love it and I've had plenty of people tell me that they've used the K18 product and noticed a drastic improvement in how their hair both looks and feels. If you're interested in optimizing your hair I have an entire YouTube video dedicated to teaching you how to achieve your fullest healthiest hair."

HotandFlashy

1.23M subs

✓Nay

"I did look at the ingredients before I used it and I wasn't thrilled with the ingredients but I liked how my hair came out at first when I first styled it but the way it frizzed up I was like absolutely not. Then I was like well no wonder with these ingredients like this has very high SD alcohol so that is going to dry out my hair and sure enough it did."

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