K18 is the industry's latest healthy hair hero - as a beauty editor I've tried every single product and these are my genuine thoughts

Despite only launching in 2020, the best K18 products have quickly become a hot commodity. The hashtag #k18results has more than a million views on TikTok and, according to the brand, when the mask first launched onto Cult Beauty it was selling at a rate of once every two minutes. 

What sets K18 apart from many other bond hair repair products is that they target the hair at a molecular level; a patented molecule (the K18PEPTIDE™) reconnects polypeptide chains in the hair as well as repairing disulfide bonds, which the brand says benefits the brand long-term. 

But with great technology often comes a greater price tag. The elephant in the room here is that K18’s products are very expensive—we are talking £30 for just 15ml of the cult leave-in mask. As a beauty editor, I test products for a living and I’ve tried every single one of K18’s, sharing my honest thoughts on each one below to help you decide if they’re worth the investment.

Here’s what you need to know about this buzzy haircare brand. 

The best K18 hair products reviewed by a beauty editor

1. K18 Peptide Prep pH Maintenance Shampoo

I love this shampoo. It’s thick and lathers nicely for a thorough clean without making your hair feel horribly dry before applying any kind of conditioner. Containing a smaller dose of the patented peptide, it’s about to be renamed Damage Shield Protective Shampoo (more on why later) and is formulated to cause minimal swelling of the hair cuticle, which helps it retain a smoother finish. Not only that, it’s colour safe and designed to be gentle on the scalp, too. I'd happily use it regularly in my routine—though, as with all K18 products, the price tag is very much an investment.

2. K18 Leave-In Molecular Repair Hair Mask

Arguably the hero product of the brand’s line-up, this K18 hair treatment is widely regarded by hair experts and beauty editors alike as one of the best hair masks. Using that aforementioned patented peptide, it offers lightweight moisture while repairing the hair for softer and healthier-feeling strands. A big plus is that it’s a leave-in treatment, getting to work in just four minutes and saving you valuable time for the rest of your styling regime.

I do genuinely notice a difference when I use it in my hair. Even the largest size is pretty dinky—£70 for 50ml—so if you’re hesitant about the price, a 5ml tube will set you back £12, allowing you to see the results in your hair before you invest in a larger size.

3. K18 Molecular Repair Hair Oil

One of the newer K18 products in the range is the techy Molecular Repair Hair Oil, featuring that patented peptide and heat protection up to 232°C as well as boosting smoothness and shine. To use, it’s very fluid and lightweight and sinks in nicely—I like to apply a little to damp hair before blow drying for extra shine. It can feel ever so slightly sticky on your hands after you’ve applied it, but not when it’s actually on your hair, which is the most important thing. As is the theme here, it’s expensive, but the good news you only need a few drops at a time because it’s so concentrated and fluid, so if you do buy a bottle it will last you a long time.

4. K18 Peptide Prep Detox Shampoo

The best clarifying shampoos are like a “reset” for your hair, only to be used every now and then to give your hair a very deep clean to remove product build-up as well as dirt and oil. This is K18’s iteration, which contains salicylic acid, activated charcoal and a smaller dose of the K18PEPTIDE™. It’s proven to whisk away 99% of product build-up, 95% of sebum and reduce copper in the hair by 76%. But despite its super deep cleaning prowess, it’s still colour safe and doesn’t feel at all harsh. 

5. K18 Damage Shield Protective Conditioner

The newest addition to the K18 line-up and soon to hit the virtual shelves is the Damage Shield Protective Conditioner, which I got my hands on ahead of its on-sale date of February 6th—and trust me, it’s a good one. Like the very best hair conditioners, it moisturises well without weighing the hair down, with a blend of ceramides as well as the patented peptide. But there’s more, as it also provides a protective shield against environmental and mechanical damage for up to three days. As for the results? While I’d still want to use a more nourishing mask from time to time, I found it left my hair feeling nice and soft and not at all weighed down.