Why Everyone Is So Obsessed With K18

TikTok has been buzzing over the #K18HairFlip, a hashtag created by hair-care brand K18, which has accumulated 10.6 billion views on the platform as of this publication. Influencers like Mikayla Nogueira (11.3 million followers) and Brad Mondo (8.7 million followers) have partnered up with the brand, and there is a treasure trove of videos reviewing its insanely popular Leave-In Molecular Repair Hair Mask. It’s been compared to Olaplex, featured in stunning before and afters, and been given the 60-second review treatment. Yeah, people love it — but at $75, it’s significantly more expensive than its competition.

So, what separates K18 from traditional bond-building products? Is it a mask or a leave-in conditioner? Which hair types can use it, and how do you use it? With the help of some cosmetic chemists and several hairstylists, here’s everything you need to know about K18 before you reach for it.

Meet the experts:

  • Suveen Sahib, cofounder of K18 and Aquis. He is based in San Francisco.
  • Krupa Koestline, a cosmetic biochemist who has worked with brands that strive to create naturally derived products. She is based in Orlando, Florida.
  • Javon Ford, a cosmetic chemist who makes his own skin-care products. On Tiktok, he shares his thoughts on popular beauty products to his 152,000-strong following. He is based in Los Angeles.
  • Natalie Ruzgis, a hairstylist at the Thrive Hair Collective in Chicago.
  • Daniel Kim, a hairstylist who works in Los Angeles, as well as Austin and Dallas, Texas.
  • Jon Reyman, a bicoastal hairstylist and cofounder of Spoke & Weal Salon, which has locations in Boston, Chicago, New York City, Nashville, Palo Alto, Los Angeles, and San Francisco.

What Is K18?

Think of your hair as a ladder that is made up of bonds. Disulfide bonds are the horizontal rungs of the ladder. There are also polypeptide chains that are the sides of the ladder, connecting the rungs vertically. When our hair undergoes any type of damage, those horizontal disulfide bonds can be broken — hence why bond builders have become more popular before, during, and after chemical treatments, explains K18 cofounder and CEO Suveen Sahib of the research he and his team did to create the product. Most bond builders make the outer structure of the hair — the hair cuticle — look smooth, glossy, and less damaged. As for the vertical polypeptide chains, though, they cannot be patched or “glued” together, which is where K18 comes in.

K18 works at a deeper level to molecularly change and repair the polypeptide chains that have been broken, as well as reconnecting the disulfide bonds. “K18 replicates the entire structure of these polypeptide chains,” says Sahib. “When they break, [K18] goes in there and reconnects them as if they weren’t damaged, bringing the chains back to the state that they were before they got chemically damaged. It mimics the structure.”

This is why the brand refers to itself as “biomimetic hair care” – biomimetic meaning “mimicking biochemical processes,” as it works to restore the hair’s original structure. We sent Orlando-based cosmetic chemist Krupa Koestline a list of K18’s ingredients, and she notes the “usual suspects” when it comes to ingredients found in hair care, such as quaternary ammonium salts, fatty acid alcohols, amino acids, and polymers. “I also see alcohol listed as a second ingredient on all of these, which can be drying to hair if it is not formulated properly,” she points out.