Rihanna, Sophie Turner and Selena Gomez Love The K18 Leave-In Hair Mask, So I Tested It on My Curls

Is it worth the hype?

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k18 leave in hair mask

As a curly gal, my haircare routine is crucial—so much that I set aside dedicated time for it every week. I often spend at least an hour in the shower just washing, detangling and conditioning my hair before I even get to any styling and drying. And since I have low porosity hair (aka moisture doesn’t like to stick around), it’s essential for me to keep conditioner on my locks longer (sometimes up to 30 minutes) before I rinse it out. So when I heard about the K18 Leave-In Hair Mask, I thought it was a joke. Could a hair mask really work its magic in four minutes without a rinse, especially on dry, color-treated curls? I decided to find out myself. Here’s my honest review after using it for a month.

What Is the K18 Leave-In Hair Mask?

This leave-in treatment promises to reverse damage in four minutes. The formula features behentrimonium chloride, which is an ingredient that our friends at Brydie report “reduces frizz and provides shine,” as well as, wheat protein to help strengthen strands, reduce breakage and improve the overall appearance of your hair. But the star ingredient in the mask is its peptide technology, which aims to repair hair damage caused by bleaching, coloring, chemical treatments, heat and daily wear-and-tear. According to the brand, the peptides can “reach the innermost layers of hair and reconnect broken keratin chains responsible for hair’s strength and elasticity.” With continued use, the hair mask is purported to strengthen strands, smooth down frizz and add softness to your hair.

What Makes the K18 Leave-In Hair Mask So Popular?

It’s become a favorite among celebrities (like Sophie Turner, Selena Gomez and Rihanna), editors and hair stylists over the last three years. It’s also racked up more than 2,000 5-star reviews on Sephora, with one reviewer saying, “This is a great hair mask. As someone with thin, dry, damaged hair, I noticed my hair looking and feeling healthier after just one use. [It’s] easy to use and repair my hair without weighing it down or making it oily.” And of course, it got in the hands of TikTokers, who can’t stop talking about the hair mask. 

The K18 Leave-In Hair Mask is also a favorite of another editor on the PureWow team. When I asked Commerce Editor Olivia Dubyak why she recommends this hair mask, she shared: “I'm not someone who usually splurges when it comes to my hair products, but I have fine, blonde hair that I get highlighted a few times a year so the bleach can cause some breakage. Last year, I went rogue and dyed my hair dark brown, and then, I started the process to go blonde again, which really did a number on my texture and ends.”

She continues, “I started incorporating the K18 hair mask at the word of a TikToker (to my defense, she is a trichologist) and my hair feels thicker and way stronger than it has in the past. I also really like that it only takes three pumps of product to coat all my hair, which helps the product last longer. For me, I started off using it for six washes in a row, and then went to using it once every few washes.”

My First Impression of the K-18 Leave-In Hair Mask

My first thought was that there was no way this small bottle would last a month. I have long, thick curls and I rely heavily on conditioner. I even laughed out loud while reading the instructions because they said to start with one to three pumps. Ma’am, have you seen my hair? Luckily, it said I could apply more if needed, which I did. I ended up using about three to four pumps per each of the eight sections of my hair. 

The scent was very subtle, which I appreciated. It has floral notes of jasmine and peony that weren’t too overpowering, but still leave a lasting fragrance on your hair. I recently hugged someone a few hours after I washed my hair, and they were quick to compliment me on how good my hair smelled (which was definitely a nice confidence booster.)

How to Use the K18 Leave-In Hair Mask

Once I finished shampooing, I worked the mask into equal sections of my hair. It’s pretty lightweight for a conditioner, especially compared to the thicker, creamier formulas I’m used to. At this point, I already felt like it wasn’t going to work for me. I was also skeptical because the instructions said to apply it on towel-dried hair. Again, I have low porosity hair, which means my locks need water to thrive. Much to my surprise, when I applied the mask to my towel-dried hair, it slipped on with ease, coating every last strand, which restored some hope. 

k18 leave in hair mask a breakdown photo of product

What Does a Beauty Editor Think About the K18 Leave-In Hair Mask?


It took some adjustment during the first week because I had never left a hair mask in before. But after week four, I realized how nice it was to cut down on my shower time. I usually spend forever completely my haircare routine, but using a leave-in hair mask made the whole process quicker and more seamless.

Whether I applied any additional styling products afterwards or not, I found that my hair was softer, bouncier and more voluminous. This leave-in mask doesn’t play around. I wouldn’t say it completely minimized frizz, but I can also blame the humid NYC summers for some of that. And I hate to be the bearer of bad news, but I dealt with some serious buildup while using this mask. Don’t get me wrong, the first two days after washing my hair were great. My curls were thriving until I hit the third day mark, at which point, my scalp was irritated and my hair felt bone dry.

Typically, I would wash my hair weekly, but because of the buildup from this mask, I had to start washing it twice a week, which was too much for me. My curls were becoming more straw-like by the day. I was starting to wonder if I was using the product correctly, but after looking at other reviews, I saw that others were having the same issue. 

Is the K18 Leave-In Hair Mask Worth the Hype? 

The K18 Leave-In Mask is marketed to all hair types, but I don’t think those with low porosity or fine hair will benefit much from using it. I also think my hair doesn’t do so well with a leave-in mask without rinsing. Yes, it leaves my hair softer and more manageable, but only temporarily. 

So, is it a scam? Not at all. There are plenty of other reviewers (including my colleague, Olivia) who stand by it. I wouldn’t say it’s the worst thing I’ve ever tried on my curls. I just think other products suit my hair better. I’m also open to trying it again in the near future—maybe I’ll use a different shampoo beforehand or another styling product afterwards to see if that helps. After all, getting your haircare routine down is a science, amiright? 

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about face matte fluid eye paint review chelsea candelario

Associate Editor, Ultimate Fangirl, Aspiring Beauty Guru

Chelsea Candelario is an Associate Editor at PureWow. She has been covering beauty, culture, fashion and entertainment for over a decade. You'll find her searching the internet...

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