TikTok's Favorite Haircare Brand Dropped a New Hair Oil—So, I Tried It

Spoiler: It saved my bleach-fried hair.

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K18 Biomimetic Hair Oil on a ski background


I just can’t resist the allure of a bowl of bleach. I’ve been highlighting and bleach-and-toning my naturally mousy blonde hair since my early teens, which means I know a thing or two about stressed-out hair—and how to help repair it. I’ve revisited my darker roots a few times in the past, but I feel my best as a bright blonde and thus aftercare is an essential step in my routine.

Because of my bleach habits, I’ve used and loved the viral favorite K18 Molecular Repair Leave-In Mask for about two years. The treatment helps repair and reconnect polypeptide chains and bonds to repair and strengthen damaged hair from the inside out. I use the treatment several times a month, forgoing conditioner and applying it to damp hair after my shower, then letting it soak in for the required four minutes before proceeding with my styling routine. My colorist credits K18 for helping my hair handle frequent bleaching and heat styling; I was previously visiting for a bleach and tone service about every six weeks.

Woman with platinum blonde hair

Kara Nesvig

When I heard K18 was launching a companion, the The K18 Molecular Repair Hair Oil ($65), I was amped. Hair oils have been a mainstay in my repertoire for years, but my old faithfuls weren’t doing it for me anymore. I’m in the process of transitioning from a bleach and tone to highlights to save on maintenance, plus dealing with some pastel pink color that simply will not fade, so my hair has been feeling a bit like a chemistry experiment. It was time to oil up.

The Product

The K18 Molecular Repair Hair Oil works in much the same way as the leave-in, helping to repair damaged hair from the inside out, which in turn helps reduce frizz and flyaways. The brand's patented K18Peptide effectively fills in the broken polypeptide chains which make up our hair, reconnecting and bonding it. Hair accepts this artificial repair as natural, and hair is improved in more than just a cosmetic sense. 

Squalane and avocado and sunflower oils go to work instantly on the surface; nourishing, smoothing flyaways, and enhancing shine. The oil also provides heat protection up to 450°F, and has some pretty impressive claims, like 24 hour frizz control and a 78% reduction in split ends. So basically, it does it all. But does it live up to the hype of its older sibling? Those are some pretty big shoes (or bottles) to fill.

K18 Molecular Repair Hair Oil
K18 Molecular Repair Hair Oil $65.00

My Review

You can use the hair oil either with the leave-in on damp hair (after you wait the magic four minutes, of course) or on dry hair to smooth frizz and add shine. For my initial test, I did both. I washed my hair as usual (skipping conditioner), then applied the treatment and three drops of the oil, following it up with a tiny bit of curl cream for definition so you could better see my natural wave pattern.

K18 Molecular Hair Oil before and after photos

Kara Nesvig

When my hair was fully dry, I squeezed two healthy droplets into my palm and scrunched them into my hair, focusing on the mid-lengths and ends where my waves feel particularly thirsty, then used the excess to gently pat down flyaways near my face. Just like the treatment, a little goes a long way, so start small at first and add more if needed. 

While some hair oils feel like they’re sitting on your hair and not fully absorbing into the strands, the K18 Molecular Repair Hair Oil actually soaks in with a lightweight finish and a clean, subtle scent that doesn’t stick around and wear out its welcome. (I have perfume for that.) For a full day after my initial application, my hair felt super soft and silky. If you have thin or fine hair, I would definitely advise practicing some restraint when applying the oil. 

The Molecular Repair Hair Oil isn’t a replacement for styling creams and lotions, but if you’re dealing with damage and dryness and can’t live without the OG leave-in cream, it’s well worth adding to your routine. If my hair could talk, she’d be saying “Thank you!”

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