By now we're all well aware of the fact that TikTok is the best spot to discover unique and effective beauty must-haves. But when it comes to the products that trend on the app, not all are created equal. Some only get five minutes of fame, with an initial video that racks up a couple of million views and inspires a few #TikTokmademebuyit follow-ups before fading from memory. But the true winners go mega-viral. When this happens, it seems like every other video you see features the product, and all your friends have suddenly started talking about it.
The K18 Leave-In Molecular Repair Hair Mask fits in the latter category. Videos about the mask have racked up a collective 12 billion views on TikTok, with everyone from beauty gurus and hairstylists to celebrities professing their love for the product. And at one point, a representative from the brand shared with us that the mask was the No. 1 trending hair care product on the app, according to the TikTok team.
TikTok users have called it a "miracle worker," adding softness and shine to hair, repairing damage and more. And some users have even added that it's better than other popular treatments on the market. But with a price tag of $75 for a full-size bottle (trial sizes start at $15), it's not something that you want to just add to your cart blindly. So we consulted with two dermatologists to get their thoughts on the product and understand how it works (and if it really does).
What is the K18 hair mask?
Founded in 2020, K18 currently only has one product available on its site for shoppers: The Leave-In Molecular Repair Hair Mask. (There is a handful more available for professionals). The mask is a leave-in treatment that is designed to help repair damage caused by bleach, color or heat and add strength, softness shine and bounce. It features the proprietary K18Peptide, which the brand says travels deeper into the inner layers of hair than other products to help reverse damage at a molecular level.
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How does the K18 hair mask work?
To understand how exactly the mask works, we first have to delve into the science of peptides. "Peptides are basically small proteins that penetrate the hair follicle and support hair growth," says Dr. Snehal Amin, co-founder of MDCS Dermatology.
Peptides stimulate collagen production, which can improve the overall health of the hair, as collagen helps to support both the hair follicle and the natural proteins in the hair, says Dr. Marisa Garshick, a board-certified dermatologist in New York City. "Additionally, when applied topically, peptides may also help to hydrate the scalp and hairs making them appear healthier," she adds.
K18 Leave-In Molecular Repair Hair Mask
Does the K18 hair mask really work?
There's a pretty good reason why the product has gotten so much hype — the experts that we spoke to agreed that the mask can be beneficial for hair. "This is a great leave-in conditioner mask," Amin says, adding that it's like a "spa for your hair."
The K18Peptide (the product's star ingredient), mimics the structure of the hair’s natural keratin to boost moisture and promote thicker hair, Amin says. The patented peptide is also designed to repair broken keratin chains, which improve hair strength, according to the brand.
"It is important to periodically do this type of hair maintenance to restore hair health especially if you are experiencing brittle, dry hair from heat, color treatment or life," he says.
And while some people might be concerned that the formula contains alcohols (they can sometimes be drying to hair), in this case, they work to your benefit. "The alcohols that are incorporated are designed to help the peptides properly penetrate the hair, so, in this case, the minimal amount of alcohol is used to help improve the delivery of the K18Peptide," Garshick says. Plus, not all alcohols are actually drying, and some types, like cetearyl alcohol (which is included in the mask), help create a physical barrier to actually keep the moisture in, she adds.
Who should use the mask?
While Amin says that anyone who is looking for softer, thicker hair can benefit from using the mask, those with dry, damaged or fine hair will see the most benefit. On a similar note, Garshick says that it's especially helpful for those with damage from bleaching, coloring and other types of processing.
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Because salt water and chlorine can stress your hair and leave it feeling dry and brittle, Amin notes that it's a great option to keep in your travel bag, too. (So you'll be happy to hear that there's a travel-sized option, too!)
How to use the K18 hair mask
The treatment is made to be applied to towel-dried hair post-shampoo. If you're planning on applying the product, you should skip the conditioner in the shower. The brand says the silicones and conditioning agents in conditioner can prevent the peptide from reaching the broken chains deep within the hair’s inner layers.
The company suggests applying one pump of the product to your hair, working from the roots to the ends (you may need more depending on your hair's thickness or length). Then, let it sit for four minutes before styling — no need to rinse! It's recommended that you use it every four to six shampoos to see lasting results.
If you're intrigued to see what all the hype is about for yourself, you can go all-in and get the full-size version above, or, if you'd rather test it out before committing, you can check out one of the trial sizes below.
K18 Leave-In Molecular Repair Hair Mask, 5mL Try-It Size
K18 Leave-In Molecular Repair Hair Mask, 15 mL Travel Size
More hair masks to try
Moroccanoil Weightless Hydrating Hair Mask
This formula was named the best overall hair mask during the 2023 Shop TODAY Beauty Awards. It's said to hydrate and condition hair to improve texture and manageability.
"My hair felt so dry before I started using this and after each time masking, it felt healthy, hydrated and smooth," Phoebe Curran, 3rd hour of TODAY producer, says. "I also noticed a nice shine to my hair once it dried."
Eva NYC Therapy Session Hair Mask
Shop TODAY associate SEO editor Kamari Stewart says that she saw a big difference in her curls after using this affordable hair mask. The brand says that it's designed to deliver 48 hours of smoothness and three times more hydration after just one use.
Virtue Restorative Treatment Mask
This mask is the one that I reach for every time I feel like my hair needs a little extra TLC. Like the K18 mask, this one is said to work on a molecular level. It's made with the brand's proprietary Alpha Keratin 60ku(R) complex, which is said to bind to areas of damage and fill them in so your hair looks and feels stronger, healthier and shinier.
Meet our experts
- Dr. Snehal Amin, MD, is a board-certified dermatologic surgeon. He is the co-founder of MDCS Dermatology and a clinical assistant professor of dermatology at Weill-Cornell Medical College.
- Dr. Marisa Garshick, MD, is a board-certified dermatologist in New York City and an assistant clinical professor of dermatology at Weill Cornell Medical College.
