01 / The basics
What is Leave-In Molecular Repair Hair Mask?
K18 describes a leave-in mask with patented K18PEPTIDE that the brand says reverses damage from bleach, colour, chemical services and heat in four minutes; shampoo without conditioner, towel-dry, apply, wait four minutes, do not rinse; vegan, colour-safe and cruelty-free per brand.
- Best for
- Post-chemical and heat-damage maintenance
02 / Review
What is in Leave-In Molecular Repair Hair Mask?
K18’s Leave-In Molecular Repair Hair Mask is built around K18PEPTIDE, a biotech peptide the brand says reconnects broken polypeptide chains and supports disulfide bonds damaged by bleach, colour, chemical services and heat. It is leave-in: the peptide stays; you do not rinse after the four-minute window.
Brand language uses “repair” and “reverse damage.” Treat those as manufacturer cosmetic claims. The Cast Index does not present K18 as a medical or laboratory service. Strength and elasticity percentages published with mist-plus-mask bleaching protocols are omitted from the catalogue fact to avoid overstating a system study.
03 / Review
What should you know about season finish — hair as silhouette?
Hair as silhouette needs length that still holds a line — soft volume, wet-slick, or deliberate undoing. Chemically worked hair frays that line. K18 is the between-salon maintenance mask that keeps texture workable so the silhouette remains a casting decision, not a damage distraction.
Use with Dream Coat when the week needs both internal soft strength and external humidity polish — mask on wash day, Dream Coat on the sleek-set day. Do not collapse both into one Amazon card note.
04 / Review
What should you know about working kit?
In shower: shampoo only — skip conditioner before K18. Out of shower: towel-dry thoroughly. Start with one pump, add by length and density, ends toward roots. Wait a full four minutes. Do not rinse. Then comb and style; add leave-in conditioner only after the window if still needed. Brand suggests intensive use for the first 4–6 washes post-service, then every few washes.
Wrong if the wearer insists on conditioning before the mask — K18 says that blocks the method. Wrong as a daily heavy cream on fine hair without dosage control. Differentiate from Olaplex No.3: No.3 is a pre-shampoo treatment; K18 is a post-shampoo leave-in.
05 / Review
What should you know about limitations and brand cautions?
Contains fragrance allergens on the INCI (e.g. geraniol, linalool, hexyl cinnamal) — check pack if sensitive. Keep out of eyes. Results vary by hair history. Clarifying shampoo first if product build-up is heavy, per brand do’s. Not a substitute for professional assessment of severely compromised hair.
06 / How to use it
How should you use Leave-In Molecular Repair Hair Mask?
- 01Shampoo; do not apply conditioner before the mask
- 02Towel-dry thoroughly
- 03Apply 1–3 pumps from ends toward roots, adding by length and density
- 04Leave for 4 minutes; do not rinse
- 05Comb and style as usual
07 / Quick facts
What should you know before choosing Leave-In Molecular Repair Hair Mask?
- —Leave-in mask; patented K18PEPTIDE (sh-Oligopeptide-78 on INCI)
- —Brand: four-minute leave-in reverse of damage from bleach, colour, chemical services and heat
- —Method: shampoo, do not condition; towel-dry; 1–3 pumps ends-to-roots; wait 4 minutes; do not rinse
- —Vegan, colour-safe, cruelty-free per K18
- —Brand clinical percentages that used mist + mask in bleaching protocols are system results — not restated here as solo-mask guarantees
- —A leave-in treatment, with different instructions from a pre-shampoo product such as Olaplex No.3
