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Leave-in molecular repair hair mask 50mL
Full-Size Leave-In Molecular Repair Hair Mask 50mL
Red curly hair before and after results using k18.
Grey curly hair before and after results using k18.
Bleach blonde hair before and after results using k18.
Red curly hair before and after results using k18.
get stronger, more resilient hair. left - 8x bleach without K18, right 8x bleach with K18
Full-Size Leave-In Molecular Repair Hair Mask 50mL
the K18 routine
Full-Size Leave-In Molecular Repair Hair Mask 50mL
less is more
works for all hair types
where does K18 fit into your routine?
Full-Size Leave-In Molecular Repair Hair Mask 50mL
Full-Size Leave-In Molecular Repair Hair Mask 50mL
K18 routine guide
tilebestseller | color:black
4.7
Rated 4.7 out of 5 stars
8,739 Reviews

full-size leave-in molecular repair hair mask

4-minute leave-in treatment to reverse hair damage
OR

Description

A leave-in treatment mask that works on the molecular level to reverse hair damage in just 4 minutes. The K18PEPTIDE™ is clinically proven to repair damage from bleach + color, chemical services and heat* – with immediate and lasting results to restore strength, softness, smoothness and bounce to hair.

20+ billion TikTok views 🔥 

*Disclaimers

Repairs Damage Caused By

  • Bleach + Color
  • Heat
  • Chemical Services
  1. Shampoo, do not condition. Towel-dry thoroughly.
  2. Apply 1-3 pumps of K18 leave-in molecular repair hair mask based on your length and density, starting at the ends and working up towards the roots.
  3. Let sit for 4 minutes. Do not rinse out.
  4. Comb, add product + style as usual. Use for 4-6 washes post-salon service, then as needed.
  • K18PEPTIDE™ is a biotech-developed peptide that mimics hair's structure to reverse damage by reconnecting polypeptide chains and disulfide bonds broken during bleaching, color and chemical services + heat*.

  • pH-optimized (5.0-6.0) to help minimize cuticle swelling + put hair proteins in their most resilient state.

  • Cream format enables easy, lightweight application across all hair types, with detangling and softening benefits.

  • Vegan, color-safe, cruelty-free.

Takes damage repair further – reconnects both polypeptide chains (and as a result, also reconnects disulfide bonds) for strength along the length + width of the hair - offering comprehensive, lasting damage repair.

Restores hair from even extreme damage - by working at the innermost layer of the hair, core strength and elasticity are renewed for strong, smooth, bouncy hair.

Delivers immediate and lasting results – hair is repaired from the first use and lasts past your next wash, for ongoing reparative benefits.

Simplified repair - convenient, leave-in formula works in just 4 minutes, with no extra rinse required.

Works on all hair types – because K18PEPTIDE™ works on a molecular level (where all hair is the same), this product is effective on all hair types.

  • DO clarify before K18 if you’re a heavy product user (demineralize for mineral + metal buildup).
  • DO apply on clean, damp hair.
  • DO wait the full 4 minutes before combing or styling.
  • DO add whatever styling products you love after the 4 minutes.
  • DO use for 4-6 shampoos consecutively for progressive results.
  • DON'T use conditioner before applying K18 Mask (you can apply after the 4 min but most find they don’t need it).
  • DON'T overdo it—less is more.
  • DON'T rinse it out.

Water (Aqua) (Eau), Alcohol Denat., Propylene Glycol, Cetearyl Alcohol, Dicaprylyl Ether, Cetyl Esters, Behentrimonium Chloride, Polysorbate 20,sh-Oligopeptide-78 (K18PEPTIDE™), Hydrolyzed Wheat Protein, Hydrolyzed Wheat Starch, Isopropyl Alcohol, Tocopherol, Phenoxyethanol, Potassium Sorbate, Citric Acid, Fragrance (Parfum), Geraniol, Linalool, Hexyl Cinnamal, Benzyl Alcohol.

pairs well with
limited edition
K18 x Future Society leave-in molecular hair mask
4.9
Rated 4.9 out of 5 stars
58 Reviews
Bestselling mask scented with Floating Forest biotech fragrance
K18 molecular repair hair oil
4.8
Rated 4.8 out of 5 stars
961 Reviews
Weightless oil that strengthens, repairs damage + reduces frizz

Description

A leave-in treatment mask that works on the molecular level to reverse hair damage in just 4 minutes. The K18PEPTIDE™ is clinically proven to repair damage from bleach + color, chemical services and heat* – with immediate and lasting results to restore strength, softness, smoothness and bounce to hair.

20+ billion TikTok views 🔥 

*Disclaimers

got questions?
Get started here.
The K18 mask works as a treatment to reverse damage in 4 minutes. It’s powered by our biomimetic K18PEPTIDE™ to seamlessly fit in and reconnect broken polypeptide chains at the molecular level. As a result, disulfide bonds are also reconnected for reinforced strength along the length + width of hair—offering comprehensive, lasting, and progressive repair.
K18PEPTIDE™ is a biotech-developed peptide that mimics hair’s structure to reverse damage by reconnecting polypeptide chains and disulfide bonds broken during damage from bleach + color, chemical services, and heat*
*Disclaimers
Conditioner leaves a film that blocks our peptide from penetrating effectively. Once the 4-minute wait time is up, feel free to use a conditioner, a leave-in, or any type of product.
We like to keep our formulas minimal, only using the exact amount of ingredients needed to get the peptide where it needs to go. Here the alcohol serves as an agent to optimize the hair environment for the K18 mask to work on a deeper level. Our unique blend of 3 alcohols functions to open the hair cuticle so the K18PEPTIDE™ can penetrate the innermost layer of hair, reaching the broken polypeptide chains (keratin chains).
Most see results after 2-3 uses. The more damaged the hair, the more dramatic the results so it may vary depending on your hair type and level of damage.

powered by K18PEPTIDE™

Biomimetic peptide clicks into hair’s keratin structure—the source of core strength—for soft, shiny, bouncy results that won’t wash away.

how to use molecular repair mask
1. Shampoo, do not condition. Towel-dry thoroughly.

2. Apply 1-3 pumps based on your length and density, starting at the ends and working up towards the roots.

3. Let sit for 4 minutes. Do not rinse out.

4. Comb, add styling product + style as usual. Use for 4-6 washes, then as needed.


*k18hair.com/disclaimers
learn more on our blog
feel what's possible with K18
See how K18 unlocks our community's expression
4.7
Rated 4.7 out of 5 stars
Based on 8,739 reviews
Reviews Summary
Customers say this leave-in hair mask transforms their hair texture and manageability after just one use. Many reviews mention noticeable improvements in softness and reduced frizz. Users with curly, fine, and color-treated hair report positive results. The mask works well for various hair types, with many noting improved texture and easier styling. While some mention the product's high price point, most find a little goes a long way. A few users recommend using conditioner alongside the mask for best results. Reviews consistently highlight the mask's effectiveness for addressing dry, brittle hair concerns.
8,739 reviews
  • Tara W.
    Verified Buyer
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 45 - 54
    Hair Concern Chemical damage, Heat damage, Frizz, Fragile/brittle hair, Dryness
    Hair Type Medium Density
    My Results Less Frizz, Bouncy Hair, Visible Difference, Defined Curl/Wave Pattern, Shinier Hair
    Rated 5 out of 5 stars
    Yesterday
    Four washes in and I am a believer

    I saw a difference from the first wash and now that I am four washes in my hair has a lot of its bounce. Back in the curls are holding much much better. Excited to continue using K28!

  • Ariana S.
    Verified Buyer
    Reviewing
    Mini Leave-In Molecular Repair Hair Mask 15 mL
    I recommend this product
    Age 25 - 34
    Hair Concern Split-Ends
    Hair Type Fine/Thin
    My Results Cleaner, fresher hair, Stronger Hair, Less Breakage
    Rated 5 out of 5 stars
    3 days ago
    Best my hair has felt

    Iv been dying my hair for 15+ years and have always had issues with damage. Was recommend by my hairstylist after use in an appointment and followed up with the mask for the next 4 washes. My hair has never felt better and Iv had significantly less split ends

  • Sofia K.
    Verified Buyer
    Reviewing
    Leave-In Molecular Repair Hair Mask Deluxe Sample
    I recommend this product
    Rated 5 out of 5 stars
    3 days ago
    No more frizzy hair

    I started using K18 about 3 weeks ago and I am super pleased with the results. With highlights, monthly root color and naturally curly hair it has become nearly impossible to control my frizzy hair. But I am astonished at the results. My hair doesn’t look like dry straw anymore. I am willing to pay the right price for a product that will make my hair look healthier and beautiful. I definitely recommend K18.

  • Danielle K.
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 55 - 64
    Hair Concern Dryness, Fragile/brittle hair, Color-care
    Hair Type Medium Density, Straight/Wavy, Grey Hair
    My Results Less Frizz, Visible Difference, Smoother Hair, Soft Touchable Hair
    Rated 4 out of 5 stars
    5 days ago
    Super soft and great humidity control

    Just started using the K18 mask. I'm pleased at how soft my processed, menopausal hair is. It's become so dry, but K18 makes it feel and look more like hair again. I was really impressed with how well it controlled humidity induced frizz too - nothing I've tried before has worked so well against humidity.

  • KanietSE K.
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 25 - 34
    Hair Concern Chemical damage
    Hair Type Fine/Thin
    My Results Less Breakage
    Rated 4 out of 5 stars
    1 week ago
    After perm

    After an unsuccessful perm, I took this mask. As it is written in the instructions, I applied only it 6 times in a row. I'm glad that the smell of burning from my hair is almost gone. Visually, the changes are not as clear as I would like, but I will continue to use. I’m sure it would be better if I give more time

    K Profile picture for K18Hair
    K18Hair
    1 week ago

    Thank you so much for taking the time to share your experience with the Leave-In Molecular Repair Hair Mask after your perm situation, KanietSE! We're really glad to hear that you're already noticing the burning smell is almost gone — that's definitely a positive sign that the mask is working to repair the damage at a molecular level.

    We completely understand that visual changes can take time to become more apparent, especially after chemical damage from an unsuccessful perm. You're absolutely right that giving it more time will likely bring better results. The molecular repair process works progressively with each use, so continuing with the treatment as you're doing is exactly the right approach.

    We really appreciate your patience and persistence with the treatment, and we'd love to hear how your hair continues to improve as you keep using the mask. Your hair has been through a lot, so the fact that you're already seeing some positive changes is really encouraging!

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