Is the K18 Leave-In Hair Mask Really a Frizz-Eliminating Godsend?

The K18 Leave-In Molecular Repair Hair Mask is an award-winning haircare product—it’s been compared to (and is purportedly more effective than) the industry standard, Olaplex’s No. 8 hair mask. K18’s hair mask has even been hailed as a replacement for conditioner. Does it actually work? Four W editors put it to the test, and gave their honest opinions.

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Allia Alliata di Montereale, Special Projects Editor

What is your day-to-day haircare routine?

I love my thick, curly, long hair, but I do very little to maintain it. My hair has a life of its own and I have accepted this. Generally, I wash my hair every other day then use a leave-in conditioner and hair oil. I rarely use hydrating treatments and have not used the K18 Peptide treatment before.

Discuss in detail your experience using this product.

My hair has been dehydrated with the sun and heat damage of summer, so this was perfect timing to try K18. It was not time-consuming. I used it every time I washed my hair for two weeks, and used about 3-4 pumps each time because of my long hair. I thought using it every time I washed my hair might be overkill, but for how coarse my hair is, it works perfectly.

How did your hair feel after? Would you use the K18 peptide hair treatment again?

I was hesitant about not using conditioner and using K18 as a leave-in conditioner instead, but it made my hair feel significantly softer. I like how it is not heavy or does not change the weight of my hair. I still used my hair oil to control frizz, but my hair is naturally on the frizzier side. I saw real results in a short amount of time. I loved it and will continue using it! This size of the bottle is also perfect for traveling this summer.

Jenna Wojciechowski, Fashion Market Editor

What is your day-to-day haircare routine?

I don’t have much of a hair routine. I usually wash it every other day and let it air dry. In my younger days, I wouldn’t leave the house without using a straightening iron—I have definitely noticed thinning in the past few years, and wonder if it stems from those heating tools. Generally speaking, my goal is to have healthy, thick hair for the rest of my life. If I had long, all-gray hair by 70, that would be fine with me.

Discuss your experience using the K18 Leave-In Molecular Repair Hair Mask.

I have never done a treatment like this one before, but it’s the type of hair regimen I can handle: low-maintenance and easy to use. I am a Capricorn, and I therefore like to adhere to rules—so naturally, I followed the directions step by step. The smell is mild and something I can definitely use daily without getting sick of.

How did your hair feel afterward? Did you see results?

My hair felt immediately softer and silkier after even one use; as it dried, my hair felt thicker, too. I was worried it was going to make my hair greasy, but it didn’t at all. It almost feels like vitamins for my hair—I can see it strengthening and repairing, too.

Would you use the K18 Leave-In Molecular Repair Hair Mask again?

Yes, I definitely would use it again—in fact, I am still using it now.

Michael Beckert, Visuals Editor

What is your haircare routine on a day-to-day basis?

My daily haircare routine consists of a cold shower and letting my hair air dry. That’s it! I’m a big believer in air drying so that your hair curls naturally. I’ll use Moroccan oil shampoo and conditioner three times a week, but I can’t shampoo any more than that, otherwise my hair will become super dry. I’m really a less-is-more kind of hair guy, so it’s safe to say I’ve never done anything like the K18 treatment before.

How did your hair feel after you used this product?

My hair felt thicker, my curls were smoother and less fried (which my hair tends to look like, especially at the end of the day), and my scalp felt really calm and clean.

Would you use the K18 Peptide Hair Treatment again?

I have used it multiple times since trying it the first time, so yes! I now use it at least once every two weeks.

Hannah Westbrook, Assistant Visuals Editor

What’s your general approach to haircare?

I’m pretty relaxed with my hair regimen, as I am blessed with thick, straight hair. I generally wash it every other day and use Moroccan Hair Oil products—I love their shampoo and conditioner. I recently got my hair colored and realized it was getting dry very easily and I use their All-in-One Leave-in Conditioner after every shower. But overall, my hair is pretty low-maintenance; I don’t use heat on it often and I only get split ends after coloring it. But I was excited to try the K18, since color treatment has definitely damaged my hair.

When using the K18 Leave-In Molecular Repair Hair Mask, did you follow the directions step-by-step or modify them at all?

I followed the instructions the first few times, but I found it difficult to remember that if I wanted to use this, I had to just use shampoo and skip the conditioner. The product has a “salon”-type smell (I’m not sure anyone will understand this, but I always feel like salon products smell better and more expensive than non-salon products. Ha!). It feels just like any other leave-in product—it was easy to brush my hair wet (which isn’t always the case) and it was a quick and easy treatment, as you don’t need to rinse it out!

How did your hair feel after? Did you see results?

I always worry that my hair will feel greasy after using moisturizing products/treatments, but this dries naturally and doesn’t leave any residue. I would say that maybe my hair is too damaged for this to repair, as I did notice it felt softer, but there definitely are still a lot of split ends in there.

Would you use the K18 Peptide Hair Treatment again?

I personally did not find this to be any kind of miracle treatment—it was nice and easy to use, but my routine that I have now is essentially the same. I don’t think there’s anything that could reverse my split ends other than getting them chopped off.