Accessibility statement Skip to content
free returns. buy with confidence
free shipping on orders $50+*
Full-Size Leave-In Molecular Repair Hair Mask 50mL
Regular price $75
Regular price $0 Sale price $75
Meta
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
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
4.7
Rated 4.7 out of 5 stars
9,394 Reviews
bestseller

full-size leave-in molecular repair hair mask

4-minute leave-in treatment to reverse hair damage

Size:
50mL
Regular price $75
Regular price $0 Sale price $75
Save Infinity
Color:
50mL

Notify me when back in stock

Leave-in molecular repair hair mask 50mL

The Full-Size Leave-In Molecular Repair Hair Mask 50mL (Size: 50mL) isn't available now, but enter your email below and we'll notify you as soon as it's back.
OR
View Full Details
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

    • ingredients

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

    • dos and don'ts
      • 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.
    • key benefits

      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.

    • more to know

      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.

    • how to use

      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.

pairs well with
FutureIQ™ biomimetic hair longevity serum
PEPTIDE PREP™ detox shampoo
Press + and − keys to zoom, arrow keys to pan.
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
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
got questions?

still have questions? visit our help center

how does the k18 mask work?

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.

what is the k18peptide™?

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

why skip conditioner?

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.

i noticed there’s alcohol in the formula, isn’t that bad for you?

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).

when should i expect to see results?

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.

soft, strong, bouncy hair for everyone

Repair damage for hair like new* in 4 minutes.

Translation missing: en.before Translation missing: en.after
before
after
"I absolutely love this product!! You have to see it to believe it!"
- Christina Marie P.
Translation missing: en.before Translation missing: en.after
before
after
“…I had my hair chopped (it was begging for it) along with some highlights and coloring of the roots. My hair stylist used this on my hair and I absolutely loved how it made my hair feel ... I love this mask so much!”
- Ashley P.
Translation missing: en.before Translation missing: en.after
before
after
"Amazing the way it feels and the shine provides to the hair instantly."
- Sandra M.
Translation missing: en.before Translation missing: en.after
before
after
"I’ve been using this mask for about four washes so far. I feel that my hair is getting healthier."
- Olga S.
Translation missing: en.before Translation missing: en.after
before
after
"It makes my hair so soft and weightless, I absolutely love it... Makes my hair feel so luxurious, it’s like I just left the salon. Can’t recommend this product more!"
- Anastasiia T.
Translation missing: en.before afer
before
after
"My hair has been a mess for years... My new hair stylist recommended K18! ... My hair looks and feels amazing with lasting results!!"
- Arnell M
before afer
before
after
"I have heat damaged color treated curly hair and this has improved my hair health immensely...This is one of those products that has incorporated itself into my routine for the rest of my life..."
- Siria A.
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.

Explore the Science EXPLORE THE SCIENCE
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
How much leave-in mask do you *really* need?
/ products
How much leave-in mask do you *really* need?
Find your optimal dose with this easy guide.
about How much leave-in mask do you *really* need?
The Science Behind K18 Molecular Repair
/ hair science
The Science Behind K18 Molecular Repair
See how our K18PEPTIDE™-powered mask reverses damage in 4 minutes for lasting...
about The Science Behind K18 Molecular Repair
The Top K18 Mask FAQs
/ products
The Top K18 Mask FAQs
answering your most-asked questions.
about The Top K18 Mask FAQs
molecular repair for curly + coily hair
/ products
molecular repair for curly + coily hair
looking to restore your natural curl pattern? you need K18.
about molecular repair for curly + coily hair
molecular repair for aging hair
/ products
molecular repair for aging hair
Hair evolves with age. This is how to support your strands throughout the years.
about molecular repair for aging hair
View All Shop all new arrivals
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 9,394 reviews
93%would recommend these products
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.
Customers Talked About
Write a Review (Opens in a new window)
9,394 reviews
  • Jenny J.
    Verified Buyer
    Reviewing
    Mini Leave-In Molecular Repair Hair Mask 15 mL
    I recommend this product
    Age 35 - 44
    Hair Concern Chemical damage, Heat damage, Color-care, Dryness
    Hair Type Fine/Thin, Straight/Wavy
    My Results Less Frizz, Smoother Hair, Soft Touchable Hair, Shinier Hair
    Rated 5 out of 5 stars
    1 hour ago
    Miracle Worker

    I've only used this a couple times but it's worked so well. I love how easy it is to use and my hair feels amazing after. Would highly recommend the product!

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    8 minutes ago

    Thank you so much for the love, Jenny! 💙 We're thrilled to hear the Mini Leave-In Molecular Repair Hair Mask is working so well for you! ✨

  • Valene A.
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 35 - 44
    Hair Concern Split-Ends, Fragile/brittle hair, Dryness, Frizz
    Hair Type Thick/Coarse
    My Results Smoother Hair, Shinier Hair, Soft Touchable Hair, Visible Difference
    Rated 5 out of 5 stars
    23 hours ago
    4c hair approved

    This mask left my hair soft, manageable and shiny. I also love the smell of it

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    21 hours ago

    Thank you so much for the 5-star review! We're thrilled to hear you're loving the Full-Size Leave-In Molecular Repair Hair Mask! 💙 So happy it's working beautifully for your 4c hair. ✨

  • Christina G.
    Verified Reviewer
    Reviewing
    Jumbo Leave-In Molecular Repair Hair Mask 100mL
    I recommend this product
    Age 45 - 54
    Hair Concern Chemical damage, Heat damage, Fragile/brittle hair, Frizz, Color-care
    Hair Type Fine/Thin, Curly/Coily
    My Results Less Frizz, Stronger Hair, Less Breakage, Smoother Hair, Soft Touchable Hair
    Rated 5 out of 5 stars
    23 hours ago
    3 years and counting

    I stopped paying for keratin and Brazilian blowouts when I found this product. I was comvimced bc Simone Biles modeled her hair before and after. Mine is natural curly but very fine, so heavy products do not work. This one does everything keratin treatments did without the cost and without the dimming effect on my blonde highlights. I use their shampoo and conditioner as well and have also used the purple toning product as well as the bounce spray. I want to try more products from K18!

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    22 hours ago

    Thank you so much for the love, Christina! 💙 We're thrilled you've been a loyal fan for 3 years and that our Jumbo Leave-In is delivering the results you love. ✨

  • Cathie S.
    Verified Buyer
    Reviewing
    Leave-In Molecular Repair Hair Mask Deluxe Sample
    I recommend this product
    Rated 5 out of 5 stars
    Yesterday
    Great Repair

    My hair was in bad shape and this leave in molecular repair helped a lot. Just bought the shampoo and regular conditioner but haven’t tried them yet. I’m optimistic though.

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    Yesterday

    Thank you so much for the 5-star review! We're thrilled the Leave-In Molecular Repair Hair Mask helped your hair so much. 💙 We can't wait to hear how you love the full routine! ✨

  • Kayla M.
    Verified Buyer
    Reviewing
    Mini Leave-In Molecular Repair Hair Mask 15 mL
    I recommend this product
    Age 35 - 44
    Hair Concern Fragile/brittle hair, Dryness, Heat damage, Chemical damage, Frizz
    Hair Type Fine/Thin
    My Results Less Frizz, Bouncy Hair, Smoother Hair
    Rated 5 out of 5 stars
    Yesterday
    Hair Magic

    Wow I’ve only used it a few times but I saw the results after 1x my hair looked incredible! Will be buying the bigger bottle

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    Yesterday

    Thank you so much for the love, Kayla! 💙 We're thrilled to hear you're seeing amazing results with the Mini Leave-In Molecular Repair Hair Mask! ✨ We can't wait for you to try the bigger bottle!

*Disclaimers

10