K18 Biomimetic Hairscience makes a short, focused range built around one patented ingredient, the K18PEPTIDE™ (sh-Oligopeptide-78). It is a biomimetic peptide: it is designed to match the structure of keratin so it can reach the cortex, the inner layer of the hair, and reconnect the broken keratin chains and disulfide bonds that bleach, colour, chemical services and hot tools leave behind. The brand was founded in San Francisco in 2020 by Suveen Sahib and Britta Cox, and Unilever announced its acquisition of K18 in December 2023.
That makes K18 different from a conditioner or a protein mask, and it also means the products only work well if you use them in the right order. This guide walks through every K18 product we carry at ProHair, what each one is for, what it costs, and the smartest way to start. Performance figures quoted below are K18’s own claims.
What makes K18 different
Most repair products work on the surface: conditioners, oils and silicones smooth the cuticle so damaged hair feels better until the next wash. K18’s peptide is built to work inside the strand. The leave-in mask is left on clean, towel-dried hair for four minutes and not rinsed, so the peptide has time to penetrate. There is no rinse-out step and no extra conditioner, which is why it fits easily into a normal wash day.
Who K18 is for
- Bleached, lightened or highlighted hair that feels gummy or stretchy when wet, or rough and straw-like when dry.
- Colour-treated hair that fades, frizzes and dulls between appointments.
- Hair damaged by daily blow-drying, flat irons or curling irons.
- Hair dulled by hard water, chlorine or product buildup.
- Fine hair that goes flat, and anyone noticing early shedding or first greys.
Who might want to look elsewhere
K18 is not cheap. The 50 ml mask is $76.79, the 30 ml oil $66.79 and the 90 ml FutureIQ serum $122.86. If your hair is uncoloured and healthy, a good professional shampoo and conditioner will serve you for less. The mask is also not a moisturiser: very dry or coily hair still needs a hydrating conditioner or leave-in on non-mask days. Every K18 formula is fragranced, and the mask contains hydrolyzed wheat protein, worth knowing if you avoid gluten.
Line-by-line breakdown
Leave-In Molecular Repair Hair Mask
The hero product. Shampoo, skip conditioner, towel-dry, apply 1 to 3 pumps, wait 4 minutes, style. K18 says it is clinically proven to repair damage from bleach, colour, chemical services and heat. Key ingredients: K18PEPTIDE™, hydrolyzed wheat protein. Sizes: 5 ml $7.15, 15 ml $29.65, 50 ml $76.79, and the 150 ml professional size at $114.65. Best for: anyone with chemical or heat damage. Shop the mask or read how to use it properly.
Weightless Molecular Repair Hair Oil
A silicone-free oil that works on two levels: the peptide inside the hair, and squalane, avocado and sunflower oils on the surface. K18 reports 24-hour frizz control, 104% more shine, 78% fewer split ends and heat protection to 450°F (232°C). Sizes: 10 ml $27.50, 30 ml $66.79. Best for: frizz, flyaways and split ends. Apply after the mask, never instead of it. Shop the oil.
Peptide Prep Detox Clarifying Shampoo
A weekly clarifying shampoo with activated charcoal and salicylic acid. K18 rates it at 99% of product buildup, 95% of sebum and 76% of copper removed in one wash, while the peptide limits protein loss. It is the ideal wash before a mask day. Sizes: 53 ml $14.29, 250 ml $40.00, 473 ml $60.36, 946 ml $102.50. Best for: hard water, swimmers, heavy product users. Shop Peptide Prep Detox.
Damage Shield Protective Shampoo and Conditioner
The everyday pair. The shampoo is pH-optimised to limit the cuticle swelling that drives frizz and colour loss, and it is certified scalp-microbiome-friendly. The conditioner uses ceramide NP, jojoba and sweet almond oils and a biotech polysaccharide, without film-forming silicones; K18 reports protection against UV, styling and environmental damage for up to 3 days. Sizes: 53, 250, 473 and 930 ml ($14.29 to $102.50 each), or the same-size Damage Shield Duo. Best for: damaged and colour-treated hair, every wash. Shampoo · Conditioner.
TripleBright Purple Shampoo
A purple foam shampoo that works three ways: an ionic detox removes the metals and minerals that trigger brass, violet pigment neutralises existing yellow, and a biopolymer helps stop metals reattaching. K18 says one wash removes up to 3 months of hard-water brass. Sizes: 125 ml $40.00, 443 ml $102.50. Best for: blonde, grey and silver hair. Shop TripleBright.
HeatBounce Leave-In Conditioning Heat Protectant
A leave-in conditioner and heat protectant in one, rated to 450°F, using K18’s resilicore™ heat-shielding technology. K18 reports 85% less breakage after blow-drying. Sizes: deluxe sample $7.15, 47 ml $24.65, 118 ml $49.29, 237 ml $82.15. Shop HeatBounce.
AstroLift Reparative Volume Spray
Volume for fine, flat hair that also repairs. K18 reports up to 25% more hair diameter and 2.5 times the volume for up to 2 days, humidity-resistant and not heat-activated. Sizes: 15 ml $7.15, 47 ml $22.50, 118 ml $47.15. Shop AstroLift.
AirWash Non-Aerosol Dry Shampoo
Translucent porous microbeads absorb oil and sweat without a white cast, and odorBIND™ traps odour. Sizes: 1.6 oz $24.65, 4 oz $49.29. Shop AirWash.
FutureIQ Nightly Biomimetic Scalp Serum
A nightly scalp serum for early shedding, thinning and first greys. In K18’s 12-week study, users saw up to 19,000 more hairs, 87% showed increased density and 70% showed fewer greys. One 90 ml bottle ($122.86) is a one-month supply. Shop FutureIQ.
K18 PRO (for salons)
The Pre-Service Molecular Repair Mist (150 ml $114.65, 300 ml $194.65) is sprayed before lightener, colour or chemical services, and the PRO Repair Starter Kit ($258.22) pairs it with the professional mask for the two-step K18REPAIR™ service. These are back-bar products for stylists, not take-home care.
Quick decision guide
- Bleached, lightened or chemically processed → Leave-In Molecular Repair Mask
- Coloured hair that fades and frizzes → Damage Shield Shampoo + Conditioner
- Buildup, hard water, swimming → Peptide Prep Detox once a week
- Brassy blonde, grey or silver → TripleBright
- Frizz and split ends → Weightless Hair Oil (after the mask)
- Blow-dry or iron daily → HeatBounce
- Fine and flat → AstroLift · oily roots → AirWash
- Early shedding or greys → FutureIQ
If you only buy one thing
Buy the Leave-In Molecular Repair Mask. You use 1 to 3 pumps on mask days only, so the 50 ml lasts months for most lengths. The cheapest way to try the full method is the Detox + Repair At-Home Duo ($86.08): a 53 ml Peptide Prep Detox Shampoo and the full 50 ml mask.
Smart buying tips
- Try before you commit: the mask comes in 5 ml and 15 ml, HeatBounce and AstroLift in trial sizes.
- Shampoos and conditioners are best value per ml in 473 ml and 930/946 ml.
- The 150 ml mask is the professional size: better value if you have long hair and mask often.
FAQ
Can I use conditioner with K18?
Not before the mask, because conditioner coats the hair. On other days, condition as normal with Damage Shield.
How often should I use the mask?
K18 suggests every wash for the 4 to 6 washes after a colour or lightening service, then as needed.
Is K18 colour-safe?
Yes. The mask, Damage Shield and Peptide Prep are colour-safe.
The bottom line
Repair with the mask, wash with Damage Shield, reset with Peptide Prep, tone with TripleBright, protect with HeatBounce, smooth with the oil. Compare every size on the K18 collection page, and read our shampoo guide, styling and scalp guide and K18 vs Olaplex comparison.