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4.7
Rated 4.7 out of 5 stars
8,180 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
PEPTIDE PREP™ detox shampoo
4.8
Rated 4.8 out of 5 stars
487 Reviews
Color-safe, non-stripping clarifying shampoo with the K18PEPTIDE™

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.
Straight bleached hair after using K18 mask.
Straight bleached hair before using K18 mask.

healthier hair with every use

Reverse damage in 4 minutes with our breakthrough K18 molecular repair technology.
the K18 difference
Feel what’s possible with fewer steps, less waste + less time.
efficacy
patented K18PEPTIDE™ powers deeper + lasting repair.
simplicity
fewer steps for a streamlined routine.
speed
results in one 4-minute use.
how molecular repair compares
how K18 works

Traveling into the innermost layers of hair, our K18PEPTIDE™ renews strength along the width AND length of hair for lasting strength where it matters.

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 8,180 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.
8,180 reviews
  • Jamilla
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 35 - 44
    Hair Concern Fragile/brittle hair, Dryness
    Hair Type Medium Density
    My Results Less Breakage, Soft Touchable Hair, Visible Difference
    Rated 5 out of 5 stars
    3 days ago
    My forever product

    I first purchased the trial package back in 2023, I loved it so I purchased the 50ml in September 2024. I just ran out of that bottle so I subscribed for a delivery every 6 months. This mask has strengthened my hair along with the other mask and conditioner I use after each wash. 2024 I also had a baby which caused my hair to thin, k18 established the bonds of my hair so that I would lose my length, my hair is still coming together after giving birth and I know this mask has done wonders for my hair. I had bad hair loss after all three of my pregnancy and this is the only product I repurchase because of the effects. Blue heart picture is 2024 and pink shirt is now 2025.

    K Profile picture for K18Hair
    K18Hair
    Yesterday

    Thank you for your review and continued support, Jamilla!

  • Rebecca H.
    Verified Buyer
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 65+
    Hair Concern Dryness, Color-care, Extending time between washes
    Hair Type Fine/Thin
    My Results Visible Difference, Bouncy Hair
    Rated 5 out of 5 stars
    4 days ago
    Best product ever

    I absolutely love this product. My hair is fine very fine and when I use this, it’s like I have tons of hair believe it or not.

    K Profile picture for K18Hair
    K18Hair
    4 days ago

    Looking great, thank you for your review and sending us over these photos.

  • Michelle J.
    Verified Buyer
    Reviewing
    Leave-In Molecular Repair Hair Mask Sample
    I recommend this product
    Rated 5 out of 5 stars
    1 week ago
    Super product

    This has repaired and strengthened my processed and color treated hair.

    K Profile picture for K18Hair
    K18Hair
    1 week ago

    We appreciate your 5-star review! Thank you!

  • Liv W.
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 18 - 24
    Hair Concern Frizz, Fragile/brittle hair, Dryness
    Hair Type Fine/Thin
    My Results Stronger Hair, Less Breakage, Smoother Hair, Shinier Hair
    Rated 5 out of 5 stars
    3 weeks ago
    Repairing my Hair🪮👩‍🔧💁‍♀️

    I have not used this product for a long time, BUT after using it I can somewhat feel my hair. The pictures I have added are what my hair currently looks like/before I used K18. I have the other products sitting in my cart ready to buy because I feel as if K18 can take my hair to the next level.

    K Profile picture for K18Hair
    K18Hair
    2 weeks ago

    Thank you for your 5-star review! If you need any product recommendations or suggestions on usage we would love to assist you.

  • Catherine M.
    Verified Reviewer
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 65+
    Hair Concern Heat damage, Color-care, Fragile/brittle hair, Frizz, Dryness
    Hair Type Medium Density, Curly/Coily, Straight/Wavy
    My Results Less Frizz, Bouncy Hair, Visible Difference, Defined Curl/Wave Pattern, Smoother Hair
    Rated 5 out of 5 stars
    3 weeks ago
    Leave in molecular repair mask

    I am totally in love with the K 18 molecular Repair mask. I just recently started using it and I’m on my third time and my hair has never looked better. It was dry and cakey looking all the time now I’ve got glorious beautiful hair.

    K Profile picture for K18Hair
    K18Hair
    3 weeks ago

    This makes us so happy to hear! Thank you for your review, Catherine.

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