Accessibility statement Skip to content
new tech is coming | Join the waitlist
free returns. buy with confidence
free shipping on orders $50+*
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
9,131 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 (K18PEPTIDE™), Hydrolyzed Wheat Protein, Hydrolyzed Wheat Starch, Isopropyl Alcohol, Tocopherol, Phenoxyethanol, Potassium Sorbate, Citric Acid, Fragrance (Parfum), Geraniol, Linalool, Hexyl Cinnamal, Benzyl Alcohol.

    • 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
K18 x Future Society leave-in molecular hair mask
Join Waitlist
K18 molecular repair hair oil
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?

Get started here.

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.

before afer
before
after
"I absolutely love this product!! You have to see it to believe it!"
- Christina Marie P.
before afer
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.
before afer
before
after
"Amazing the way it feels and the shine provides to the hair instantly."
- Sandra M.
before afer
before
after
"I’ve been using this mask for about four washes so far. I feel that my hair is getting healthier."
- Olga S.
before afer
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.
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 9,131 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)
9,131 reviews
  • Elvira L.
    Verified Reviewer
    Reviewing
    Mini Leave-In Molecular Repair Hair Mask 15 mL
    I recommend this product
    Age Under 18
    Hair Concern Fragile/brittle hair, Heat damage, Oily hair/scalp, Split-Ends, Frizz
    Hair Type Medium Density
    My Results Less Frizz, Bouncy Hair, Visible Difference, Stronger Hair, Less Breakage
    Rated 5 out of 5 stars
    4 hours ago
    Saved my hair

    I’ve been on the hunt for a leave-in hair product that doesn’t weigh my hair down or leave it looking greasy. My hair is very brittle and has never been able to grow past a certain length.

    I’ve been using this for over a month now, and my hair feels so much stronger. I notice way fewer split ends than I used to, and my hair is shinier and softer. Out of all the leave-in products I’ve tried, this is the only one that doesn’t weigh my hair down or irritate my scalp. I’m genuinely impressed and will definitely keep repurchasing it.

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

    Thank you so much for your amazing review, Elvira! 💛 We're thrilled to hear our Mini Leave-In Mask has transformed your hair. Here's to continued strength and growth! ✨

  • Amrita S.
    Verified Buyer
    Reviewing
    Full-Size Leave-In Molecular Repair Hair Mask 50mL
    I recommend this product
    Age 25 - 34
    Hair Concern Heat damage, Chemical damage, Fragile/brittle hair
    Hair Type Fine/Thin
    My Results Stronger Hair, Less Breakage
    Rated 5 out of 5 stars
    14 hours ago
    Instant difference

    I have very poor quality hair postpartum which break so often. I have used K18 and in a week the breakage has reduced substantially. I had also done keratin sometime ago and needless to say K18 is slowly overturning the damage.

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

    Thank you so much for your amazing review, Amrita! 💛 We're thrilled to hear the Leave-In Molecular Repair Hair Mask is helping reduce breakage and restore your hair's health. Here's to stronger, healthier hair days ahead! ✨

  • Rachel M.
    Verified Buyer
    Reviewing
    Leave-In Molecular Repair Hair Mask Deluxe Sample
    I recommend this product
    Rated 5 out of 5 stars
    2 days ago
    Smooth and Healthy Hair

    This hair mask has transformed my hair. It has strengthened and softened my white/grey hair. Truly an incredible product. Nothing compares!!

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    2 days ago

    Thank you so much for your amazing review, Rachel! 💛 We're thrilled to hear our Leave-In Molecular Repair Hair Mask has transformed your hair. Your support means the world to us! ✨

  • Sara A.
    Verified Buyer
    Reviewing
    Mini Leave-In Molecular Repair Hair Mask 15 mL
    I recommend this product
    Age 25 - 34
    Hair Concern Chemical damage, Heat damage, Color-care, Frizz, Fragile/brittle hair
    Hair Type Thick/Coarse, Straight/Wavy
    My Results Less Frizz, Stronger Hair, Less Breakage, Cleaner, fresher hair, Soft Touchable Hair
    Rated 5 out of 5 stars
    1 week ago
    saved my hair

    I get my hair bleached and toned every 3 weeks as a natural dark haired girl and it keeps it from not only being stringy, damaged and frizzy but it helped with the thinning too and I get complimented on how healthy it is every time I go to get it done

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    1 week ago

    Thank you Sara! We're thrilled the Mini Leave-In Molecular Repair Hair Mask is keeping your bleached hair healthy and strong. We appreciate your amazing review! ✨

  • Loretta C.
    Verified Buyer
    Reviewing
    K18 x Future Society Limited Edition Scent Mask
    I recommend this product
    Age 55 - 64
    Hair Concern Chemical damage, Frizz
    Hair Type Thick/Coarse
    My Results Visible Difference, Less Frizz, Less Breakage, Smoother Hair, Cleaner, fresher hair
    Rated 5 out of 5 stars
    1 week ago
    Love this leave in

    I love this i wish the jumbo leave in had the limited sent tho

    Was this helpful?
    K Profile picture for K18Hair
    K18Hair
    1 week ago

    Thank you so much Loretta! We're thrilled you love the limited edition scent. We appreciate your feedback and your 5-star review! ✨

*Disclaimers

10