K18 Leave-In Molecular Repair Hair Mask 5ml is a single-use travel size of the cult bond-repair treatment that helped redefine the at-home haircare category. Built around the patented K18PEPTIDE — a bioengineered peptide designed to slot back into broken keratin chains — the mask works in just four minutes to help reverse damage from bleach, colour, chemical services and heat styling. The 5ml format is a generous trial size, enough for a single full-head application on most hair lengths.
About K18
K18 is a US biotech-led haircare brand that launched in 2020 after roughly a decade of bond-repair research. The brand's hero ingredient, K18PEPTIDE (sh-Oligopeptide-78), is a small, lab-developed peptide engineered to mimic the structure of hair's own keratin and reach into the inner cortex, where it helps reconnect broken polypeptide chains and disulfide bonds responsible for strength and elasticity.
Key ingredients
- K18PEPTIDE (sh-Oligopeptide-78): The patented bioactive peptide at the heart of the formula, designed to reach into the cortex of the hair shaft and help repair broken bonds.
- Hydrolyzed Wheat Protein & Wheat Starch: Add temporary smoothness and help the mask deposit evenly along the hair shaft.
- Behentrimonium Chloride: A conditioning agent that helps the formula slip through tangles.
- Tocopherol (Vitamin E): Added antioxidant support for the formula.
What it does
- Helps repair the look and feel of damaged hair from within over a 4–6 wash cycle.
- Restores softness, bounce and elasticity to chemically treated and heat-stressed hair.
- Reduces the appearance of frizz and split-end-style breakage.
- Leave-in formula — no rinsing required, so the peptide stays in contact with the hair.
Who it's for
Designed for anyone whose hair is showing signs of damage — bleached blondes, frequent colour clients, relaxed or chemically straightened hair, or hair that feels dry and gummy after heat tools. Suitable for all hair types, all hair textures and colour-treated hair, and safe for use after relaxers, perms and keratin services. The 5ml size makes it ideal for travel, holiday and weekend bags, or for trying the brand before committing to a full-size bottle.
How to use
- Shampoo thoroughly. Do not condition.
- Towel-dry the hair well — the formula works best on damp, not soaking wet, hair.
- Dispense one to three pumps depending on length and density.
- Emulsify between the palms, then work through the hair starting at the ends and moving up towards mid-lengths and roots.
- Leave for at least 4 minutes — do not rinse.
- After the 4-minute wait, apply any other styling product (leave-in, oil, heat protectant) as normal and style.
- Use on every wash for the first 4–6 washes for the most noticeable repair, then as a maintenance treatment once or twice a week.
Specifications
- Size: 5ml (travel/trial size)
- Format: Leave-in repair mask
- Hair type: All types, especially damaged, colour-treated and chemically processed hair
- Brand: K18 Biomimetic Hairscience
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