"Does the K18 molecular repair range actually fix damage? Here's my honest review" (2024)

Bond-building hair treatments are everywhere you look nowadays. While we all used to strive to get the perfect balayage or nail the messy bun, all our hair goals have pivoted towards healthy, glass-like strands (well, as close as we can get to that, anyway). Enter: K18.

The molecular repair range – in particular, the K18 Leave-in Molecular Repair Hair Mask (from £30) – has gone viral on social media for its damage-repairing powers (so much so that Hailey Bieber is reportedly a fan, as well as Sofia Richie Grainge), so I thought it was worth putting it through the biggest test of them all: trying to give my frazzled, damaged, coloured locks a new lease of life.

If you've been wondering if the K18 haircare range is really worth the hype (and money), keep scrolling.

Does K18 actually work?

Even some of the best 'damage repair' hair ranges out there has only been a temporary fix for my strands, so I was intrigued by K18's long-lasting repair claims.

"K18PEPTIDE™ is in all our products and is an incredible peptide that can reverse damage at a molecular level in the polypeptide chain, renewing strength and elasticity on all hair types," explains Jordan Alexander, Senior Director of Global Education at K18.

Yep, that's right, you can use K18 products on all hair types, textures and colours (even if you're a bottle redhead like Moi).

Is K18 better than Olaplex?

I've tried a lot of hair-bonding treatments out there (read my review of my go-to serum here) and I never found Olaplex did quite enough for me, so would K18 be different?

"Our K18PEPTIDE™ – a unique amino acid sequence – works on a molecular level to restore hair back to like-new strength," says Alexander. "By reaching the innermost layers of hair and reconnecting broken keratin chains (the result of bleaching, chemical services, and heat damage) the peptide provides lasting renewal instead of temporarily patching damage like other bond-building products on the market," he adds.

Spoiler: I did find it worked better than you-know-who, and the results weren't just flushed down the drain in the next wash (whether I was using K18 products or not).

How to use K18

The first mistake I think you can make with this range is using it like your normal haircare range. In fact, I had to have my phone at the side of the shower just to make sure I got this exactly right (risky but necessary).

Here's a guide on how to use the K18 range for the first time:

How to use the K18 Peptide Prep Detox Shampoo...

For your first time using K18, wash twice with the K18 Detox Shampoo. Do not use conditioner. Get out of the shower and gently towel dry your hair, removing most of the moisture. Do not brush, instead separate hair gently with hands/fingers.

How to use the K18 Leave-in Molecular Repair Hair Mask...

K18 Leave-In Molecular Repair Hair Mask

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (3)

Depending on length and thickness, use one or two pumps of the K18 Leave-In Molecular Repair Mask into your hands, remember less is more. If using the 15ml bottle, three to four. Spend time working the product into a thick white paste. Do not apply to hair until it is at this consistency. Start at the ends and pat the white paste onto the hair and then work up to the mids and roots. Do not brush and leave for 4 mins. Once time is up, brush hair through.

How to use the K18 Molecular Repair Hair Oil...

Now to the oil. Less is more (K18 really emphasises this, to the point where it scared me). Use 2-3 drops of the K18 Molecular Repair Hair Oil on wet hair. Once hair is brushed through, work 2-3 drops of oil into your hands and then pat onto ends and work up to mid-length and roots.

And yes, K18 says you can use this regime every day if you're a daily hair-washer (although, it might be pricey).

"For optimal results, we recommend using the full K18 at-home damage repair routine (detox shampoo > mask > oil) for 4-6 consecutive washes and then you can reduce use to once every 3-4 washes (as needed) to maintain hair strength," says Alexander.

Is K18 worth the hype?

I'm glad you asked, this is what I'm here for. I put the hair-bonding treatment range to the test with my coloured, wavy and fairly damaged hair to see if it actually improved its condition and texture.

Here's my honest review...

My K18 review

Due to the (what I think of as) very specific instructions of this range, I was nervous I was going to f*ck it up – not a great start. Once my hair was damp, I went to apply my shampoo. Now, warning: it's as black as my soul and like no shampoo I've ever encountered. Weird, to say the least, but you've been warned.

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (7)

Shampoo: Halloween edition

I'd never usually wash my dry hair twice, but I'm a teacher's pet and followed their instructions (even though my hair was so knotty afterwards I cringed).

Next up, the famous K18 mask. I know it said only 2-3 pumps, but this wasn't enough to cover my long-ish lengths, so I added another pump for good measure. I was intrigued at how this was going to repair my strands in just four mins; usually, I leave my hair mask on for All Too Well (10-minute version) but this was aiming to repair in the same amount of time as the OG song length (both Taylor's Version, obvs).

To finish off, I applied three drops of the oil. Again, my hair needs a 20p-sized amount of oil, so I did add a bit more than advised. It's not got a greasy texture like most hair oils I've tried, which was surprising.

The final result

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (9)

My hair before washing vs. after one use of K18

If this was the result after just one wash, sign me up. This was my hair after applying just the three K18 products, which is way more streamlined than my usual routine. It's clear to see just how much shinier my hair was, as well as a reduction in frizz. Plus, my hair colour looked way more vibrant. It's a yes from me.

However, due to the lack of styling products used, my hair did get fluffier than normal once I went out into the wild (read: around central London). Overall, my hair was softer and shinier for days after, with no bedhead-induced matting at the back of the head to be seen.

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (11)

My hair on day four after wash day still looking shiny and soft

My only comment is that, while they warn you that less is more, I don't think this can be said for all hair types and textures (like they claim to serve). How much product your hair needs depends on its porosity, so I think the brand should acknowledge this a bit more. If you have thin pin-straight hair, sure, be careful, but if you have curlier hair than me, be prepared to use a bit more.

As with most haircare ranges, if you're the latter, you will get through these products quickly, which means it's going to be quite spenny. However, I definitely think it's worth starting a healthy hair journey with this range – there's no debating the glossy results.

K18 Repair Starter Set

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (13)

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (14)

Charlotte Bitmead

Senior Beauty Writer

Charlotte Bitmead (she/her) is the Senior Beauty Writer at Cosmopolitan UK. She has over six years experience writing about beauty and has previously written for ELLE and The Sunday Times Style, covering everything from politics to sustainability to inclusivity within the beauty industry. When she’s not writing in-depth features, testing out the newest skincare fad or trying to decide what nail art to get, you can find her overspending in bookshops or shouting at Arsenal matches. Find her on LinkedIn

"Does the K18 molecular repair range actually fix damage? Here's my honest review" (2024)
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