K18 is one of those haircare brands that’s everywhere at the moment. The four-minute mask is the famous one, and there’s a whole range built around it now. I always want to know what’s in the bottle before I recommend anything, and with K18 the ingredient list turned out to be the most interesting part. There’s one ingredient in particular, sitting at number nine on the back of the mask, that the whole brand is built on.
So I went through five of K18’s best-known products. The mask, the detox shampoo, the Damage Shield shampoo and conditioner, and the new FutureIQ scalp serum. Every ingredient list, every claim, and where each one is sold, because (and this matters more than you’d think) the UK and US versions of K18 are sold through completely different shops.
The short version
K18’s star ingredient is sh-Oligopeptide-78, which the brand calls K18PEPTIDE. It is in the Leave-In Molecular Repair Hair Mask, the Peptide Prep Detox Shampoo and both Damage Shield products, but it is not on the ingredient list for the FutureIQ serum. If you only buy one K18 product, buy the mask (from £30 for 15ml at Sephora UK). The detox shampoo is a once-a-week clarifier with salicylic acid and charcoal. FutureIQ is a nightly scalp serum (£110 in the UK, $120 in the US) and its hair and gray results come from K18’s own 12-week study. In the UK, buy K18 from Sephora UK. In the US, buy from K18 direct or Sephora US.
Table of Contents
What K18 actually is (and what the peptide does)
K18 is a haircare brand built around one patented ingredient. On the label it’s written as sh-Oligopeptide-78, and K18 brand it K18PEPTIDE. Their pitch is that it’s the right size and shape to get into the inner layers of the hair and reconnect the broken keratin chains that give hair its strength and stretch. That’s the brand’s explanation, not mine, and I’m not a chemist. But it’s the whole reason the brand exists, so it’s worth knowing what to look for on the back of the bottle.
The bit I found most useful: four of the five products below contain it. One doesn’t. I’ll get to which one.
K18 Leave-In Molecular Repair Hair Mask: ingredients and benefits
Buy the K18 mask▾See the UK and US options
This is the famous one.
It’s a leave-in, which confuses people. You shampoo, you don’t condition, you towel dry, then you work it through from ends to roots and leave it alone for four minutes before styling. Sephora UK’s directions say start with 1 mL (about a dime-sized amount), with 2 mL as the average, and use it for the first four to six washes before dropping to “as needed”.
Full ingredient list (Sephora UK): 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.
The ones doing the work, as I read it:
sh-Oligopeptide-78 (K18PEPTIDE) is the repair peptide, ninth on the list. K18’s own clinical claim is that on hair bleached 8 times, after 2 uses, it restored damaged hair by up to 82%. Behentrimonium chloride and cetearyl alcohol are the softening, detangling part, the stuff that makes hair feel conditioned without you actually using conditioner. Hydrolyzed wheat protein and hydrolyzed wheat starch sit right after the peptide, which matters if you avoid wheat. Tocopherol is vitamin E.
One thing I always clock on a leave-in: alcohol denat. is second on the list. I’m not saying that’s a problem, just that its there and it’s high up. And the fragrance brings geraniol, linalool and hexyl cinnamal with it, so if you react to fragrance allergens, that’s your heads up. The scent itself is described as light floral, jasmine and peony.
What people say about the K18 mask, and my verdict
If there is one K18 product that has dominated the haircare conversation, it has to be the K18 Leave-In Molecular Repair Hair Mask. It is one of those products that seems to inspire either “where have you been all my life?” or “I genuinely don’t understand the hype”, with very little middle ground.
The appeal is obvious if your hair has been through bleach, color, heat styling or chemical treatments. K18 is designed to repair damage at a deeper level, and that’s the whole pitch.
One thing that kept coming up when I looked through reviews was that you really don’t need much product. Some people initially used far too much and ended up with hair that felt sticky, coated or even drier. Reddit users repeatedly recommended starting with a tiny amount and adding more only if necessary.
The four-minute wait is another part of the K18 routine that takes a little getting used to. This isn’t a traditional rinse-out hair mask that you slap on, leave for ten minutes and rinse away. The idea is to give the treatment time to work before continuing with your styling routine.
And when it works, the feedback is impressive. I’ve seen people with heavily colored or bleached hair say that their hair feels softer, stronger and much less prone to breakage after incorporating K18 into their routine. One Reddit user with color- and heat-treated hair said they noticed a difference after several uses and liked the reduction in breakage and split ends.
But I wouldn’t call this a guaranteed miracle product. There are also plenty of people who say it did very little for their hair, or initially made their hair feel rough, gummy or dull. Some users found that it took several applications before they noticed an improvement, while others simply decided it wasn’t compatible with their hair.
My verdict: K18 is one of those expensive treatments where technique really matters. Don’t drown your hair in it, don’t treat it like a conventional mask and don’t expect one application to transform severely damaged hair overnight. If your hair has significant chemical or heat damage, though, I can see why this has developed such a cult following.
K18 Peptide Prep Detox Shampoo: ingredients and benefits
Buy the detox shampoo▾See the UK and US options
This one’s a scalp product as much as a hair one, which is why it caught my eye.
Full ingredient list (via INCIDecoder): Water (Aqua) (Eau), Sodium C14-16 Olefin Sulfonate, Cocamidopropyl Hydroxysultaine, Salicylic Acid, Charcoal Powder, SH-Oligopeptide-78, Panthenol, Glycerin, Sodium Phytate, Guar Hydroxypropyltrimonium Chloride, Caprylyl Glycol, Caprylhydroxamic Acid, Citric Acid, Potassium Hydroxide, Sodium Hydroxide, Fragrance (Parfum), Benzyl Salicylate, Limonene.
Salicylic acid is the headline for me. K18 say it clears sebum buildup without stripping hair of its moisture and lipids. Charcoal powder is there to absorb oil, dirt and buildup, per the brand. Sodium phytate is a chelator, which is the bit that grabs onto metals, and K18 specifically pitch this shampoo at the metals in tap and hard water. The K18PEPTIDE is in here too, where K18 say it helps reduce protein loss during washing.
K18’s own test, on a bleached hair tress after one wash: 99% of product buildup removed, 95% of sebum removed, 76% of copper removed. It’s meant to be used once a week, swapped in for your normal shampoo, not every wash.
For anyone else with seb derm (I’ve written loads about wearing a topper with seborrheic dermatitis), SkinSort labels this one fungal acne (malassezia) safe. That’s SkinSort’s label, based on the ingredient list, not a promise it’ll suit your scalp. But it’s a better starting point than most clarifiers I’ve looked at.
What people say about the detox shampoo, and my verdict
A detox shampoo is one of those products that can either be incredibly useful or leave your hair feeling like you’ve washed it with dish soap.
The K18 Peptide Prep Detox Shampoo is designed to remove buildup while avoiding that horrible stripped feeling, which appeals if you use styling products, dry shampoo, oils or silicone-heavy products regularly.
What I like about the concept is that it isn’t simply about making your hair squeaky clean. The idea is to create a clean base so that the rest of your haircare routine can do its job.
Feedback around this one is surprisingly positive. Users describe it as a detox shampoo that cleans thoroughly without leaving their hair feeling excessively stripped, and one recent discussion specifically praised it for being a favorite because it didn’t leave the hair feeling dry or harsh. Another user with high-porosity hair said they liked it for helping with damage and breakage.
I also like that this isn’t necessarily an everyday shampoo. A detox shampoo makes much more sense as an occasional reset, especially if your hair starts feeling heavy, coated or strangely dull despite using products that normally work well for you.
The price is something to consider, but another Reddit user pointed out that the K18 detox shampoo can last a long time because only a small amount is needed and it is used as the second shampoo rather than being your everyday cleanser.
Bottom line for me: if your hair regularly deals with product buildup, oils, dry shampoo or that mysterious “why does my hair feel dirty when I literally just washed it?” problem, this is the K18 product I’d reach for as an occasional reset. It’s a much more targeted product than a standard shampoo, so I wouldn’t use it every wash.
K18 Damage Shield pH Protective Shampoo: ingredients and benefits
Buy the Damage Shield shampoo▾See the UK and US options
If the detox shampoo is the once-a-week reset, this is the everyday one.
Quick bit of history that cleared up a lot for me. K18’s help centre says this is the same formula as the old Peptide Prep pH Maintenance Shampoo. Just a new name. So if you loved that one, you haven’t lost it.
Full ingredient list (via INCIDecoder): Water (Aqua) (Eau), Sodium C14-16 Olefin Sulfonate, Cocamidopropyl Betaine, Sodium Methyl 2-Sulfolaurate, Sodium Lauryl Sulfoacetate, SH-Oligopeptide-78, Panthenol, Glycerin, Sodium Phytate, Guar Hydroxypropyltrimonium Chloride, Disodium 2-Sulfolaurate, Caprylyl Glycol, Caprylhydroxamic Acid, Benzoic Acid, Citric Acid, Sodium Hydroxide, Sodium Chloride, Fragrance (Parfum), Limonene. K18’s own US product page lists a few more fragrance components on the end (hydroxycitronellal and some citrus oils), so check the bottle you actually get.
The point of this one is the pH. K18 say it sits at 4.5 to 5.5, which is meant to stop the hair cuticle swelling up while you wash, and that’s where the less frizz, less tangling, color-lasting-longer claims come from. Panthenol and glycerin are there for moisture and guar hydroxypropyltrimonium chloride helps with slip. In K18’s consumer test of 35 people over 21 days, 91% said hair looked healthier, 91% said it felt smoother, and 91% said it didn’t feel weighed down. Those numbers are what people said about their own hair.
What people say about the Damage Shield shampoo, and my verdict
The K18 Damage Shield pH Protective Shampoo is designed to be the everyday counterpart to the more intensive Peptide Prep Detox Shampoo. The focus here is gentler: keeping the hair clean while supporting its condition and protecting it from everyday damage.
And honestly, this is probably the part of the K18 range that interests me most because an everyday shampoo has a much bigger job to do than a treatment you use occasionally.
The feedback is mixed, though. There are people who love the K18 shampoo and conditioner combination, mostly for the softness it gives their hair. But there are also users who didn’t notice any meaningful improvement and preferred other shampoos that gave them better results for less money.
There are also some reports of scalp irritation, including one Reddit user who experienced tenderness, itching and a burning sensation after using the Damage Shield shampoo and stopped using it. That’s one person’s experience and it won’t be everyone’s, but I’d want to know if my scalp was sensitive.
That’s the thing with K18. The brand has a very strong reputation for repairing damaged hair, but that doesn’t mean every product in the range will be perfect for every head of hair.
If your main priority is maintaining softness, reducing the feeling of dryness and keeping chemically treated hair looking healthy between treatments, the Damage Shield shampoo makes sense. If your hair is heavily coated with styling products or buildup, I’d reach for the Detox Shampoo instead.
My take: a good option if you want an everyday shampoo that sits within a damage-protection routine rather than a heavy-duty detox. But because shampoo is something you’ll potentially use several times a week, I’d pay particular attention to how your scalp and hair actually respond.
K18 Damage Shield Protective Conditioner: ingredients and benefits
Buy the Damage Shield conditioner▾See the UK and US options
Remember the “don’t condition before the mask” rule? This conditioner is for the days you’re NOT using the mask. K18 are clear that the two do different jobs. The mask is repair, the conditioner is protection.
Full ingredient list (via INCIDecoder): Water (Aqua) (Eau), Isopropyl Palmitate, Stearyl Alcohol, Propanediol, Isopentyldiol, Behentrimonium Chloride, Tocopherol, Tocopheryl Acetate, SH-Oligopeptide-78, Alteromonas Ferment Extract, Prunus Amygdalus Dulcis (Sweet Almond) Oil, Simmondsia Chinensis (Jojoba) Seed Oil, Phospholipids, Jojoba Esters, Calcium Gluconate, Hydroxypropyl Guar Hydroxypropyltrimonium Chloride, Ceramide NP, Phytosteryl/Isostearyl/Cetyl/Stearyl/Behenyl Dimer Dilinoleate, Polyquaternium-16, Stearalkonium Chloride, Isopropyl Alcohol, Butylene Glycol, Gluconolactone, Phenoxyethanol, Sodium Benzoate, Citric Acid, Sodium Hydroxide, Fragrance (Parfum), Hydroxycitronellal.
This is the richest formula of the five. Ceramide NP is the one K18 lean on, as part of what they call a fortifying ceramide blend that seals damage sites in the cuticle. They also talk about a biotech-produced polysaccharide as a shield against pollution. Sweet almond oil, jojoba seed oil and jojoba esters bring the softness (and the almond oil is worth knowing about if you avoid nuts). Vitamin E shows up twice, as tocopherol and tocopheryl acetate, and the K18PEPTIDE is in here too.
K18’s claim is conditioning protection against UV, environmental aggressors and mechanical styling for up to 3 days. They also report an 81% breakage reduction on a bleached tress after 50 cycles of UV and washing, compared with a tress that didn’t get the conditioner. One thing people ask: it doesn’t have SPF. K18 say so themselves. It goes on mid-lengths to ends, not the scalp.
What people say about the Damage Shield conditioner, and my verdict
The K18 Damage Shield Protective Conditioner takes a slightly different approach from the molecular repair mask. The mask is what you reach for when your hair is already damaged. This is more about maintaining the condition of your hair and protecting it from the everyday abuse that adds up over time.
Think heat styling, brushing, washing, environmental exposure and all the other little things we don’t necessarily consider damage until suddenly our ends are looking decidedly unhappy.
The biggest appeal here is the texture. K18 positions this as a lightweight conditioner, which makes sense because damaged hair doesn’t necessarily need to be buried under a thick, heavy conditioner every time you wash it.
I’d still keep expectations realistic. Online discussions around the K18 range show just how differently hair can respond to these products. Some people love the softness they get from the shampoo, conditioner and mask combination, while others have reported that continued use made their hair feel unusually thin or that they preferred going back to another brand.
There’s also a broader criticism that comes up with K18: because the products are relatively expensive, you want to know that you’re getting something genuinely different rather than simply paying more for hair that feels temporarily softer.
For me, that’s where the Damage Shield Conditioner makes more sense as part of a complete routine than on its own. The K18 mask is the treatment; the conditioner is the maintenance step.
Who it’s for: this is the product I’d look at if you want lightweight softness and protection without turning your hair into a heavy, over-conditioned mess. If your hair is extremely dry and loves rich masks and conditioners, however, you may find this isn’t quite enough on its own.
K18 FutureIQ Hair Longevity Serum: ingredients, claims and who it’s for
Buy FutureIQ▾See the UK and US options
Okay. This is the one with the biggest claims, so it gets the longest look.
FutureIQ launched on August 5, 2026. It’s a nightly scalp serum, fragrance free, and it’s aimed at what K18 call premature hair aging: shedding, early grays and an aging scalp. You put four droppers on a damp or dry scalp, massage in, don’t rinse. One bottle is roughly a month.
Full ingredient list (SkinSort, matching a retailer listing): Water, Pentylene Glycol, Dimethyl Isosorbide, Glycerin, Niacinamide, Polysorbate 20, Sodium Benzoate, Hydroxyethylcellulose, Lysine Carboxymethyl Cysteinate, Citric Acid, Zinc Sulfate, Palmitoyl Dipeptide-52, Hydrolyzed Yeast Protein, Potassium Sorbate, Disodium Phosphate, Polysorbate 60, Palmitoyl Tetrapeptide-20 Amide, Sodium Phosphate, Sodium Nitrate.
Remember that ingredient at number nine on the mask? I couldn’t find sh-Oligopeptide-78 on this list. FutureIQ uses different peptides, palmitoyl dipeptide-52 and palmitoyl tetrapeptide-20 amide, alongside niacinamide, zinc sulfate and hydrolyzed yeast protein. K18 call the whole system MultiVital and describe it as biomimetic peptides, a root-anchoring complex and antioxidants. So it’s a K18 product, but it isn’t the K18 peptide.
The results K18 publish come from their own 12-week clinical study. At month one, 100% showed reduced hair fall. At month two, up to 10,000 more hairs and 87% showed increased density. At month three, 70% showed fewer grays and up to 19,000 more hairs. Those are big numbers, and they’re the brand’s numbers. I’d love to see how they hold up outside a brand study, and it’s too new for that yet.
Who is it for? The retailer page on CosmoProf says it works best for people with less than 30% gray and minimal to moderate shedding, and that it isn’t a replacement for root coverage. I write about hair loss, so I’ll add this. If you’re losing a lot of hair, or it’s come on suddenly, get it looked at by your doctor or a dermatologist before you spend £110 on a serum. FutureIQ is a cosmetic scalp serum, not a hair loss treatment.
What does K18 smell like?
The fragrance is worth a mention with K18, because it’s one of those it-depends-who-you-ask situations.
The Leave-In Molecular Repair Hair Mask smells fairly subtle to me, a lot lighter than a heavily perfumed hair treatment. K18 describes the fragrance as a light floral, with jasmine and peony notes, but interestingly, Reddit is much more divided about how it actually smells in the hair. Some people describe it as barely noticeable or almost cream-like, while others have reported a distinctly chemical, rubbery or just generally odd smell.
I think this is useful to know before buying because fragrance is so personal. There are people who love the results of the mask but dislike the scent, and there are even reviews from fragrance-sensitive users saying that the fragrance was too strong for them. Some users say the smell disappears once the hair is dry.
For me, I’d describe the overall K18 fragrance as clean, slightly floral and quite understated, rather than the big, luxurious salon scent you get from some premium haircare brands. If you want your shampoo and conditioner to leave your hair smelling strongly perfumed for hours, K18 probably isn’t the range I’d choose purely for fragrance.
The Damage Shield shampoo and conditioner scent
The Damage Shield Shampoo and Conditioner have a much more traditional haircare feel fragrance-wise. They’re not what I’d call intensely perfumed, and that’s a positive for me because I don’t necessarily want my haircare competing with my perfume.
What surprised me when reading through other reviews is that scent doesn’t seem to be the main complaint about the Damage Shield products. The conversations tend to focus much more on how the products affect softness, texture and the scalp. There are individual reports of irritation from the shampoo, though, including itching, tenderness and a burning sensation, so anyone with a particularly sensitive scalp should keep that in mind.
So if you like subtle, clean haircare scents more than a huge blast of perfume, K18 is probably going to be more appealing. If you buy hair products partly because you want that “I just left the salon and my hair smells incredible” effect, this isn’t really what K18 is about.
Which K18 product should you buy? A quick comparison
| Product | What it’s for | Key ingredients | Has K18PEPTIDE? | How often |
|---|---|---|---|---|
| Leave-In Molecular Repair Hair Mask | Repairing damage from bleach, color, chemical services and heat | sh-Oligopeptide-78, behentrimonium chloride, hydrolyzed wheat protein | Yes | First 4 to 6 washes, then as needed |
| Peptide Prep Detox Shampoo | Clearing buildup, oil and hard-water metals | Salicylic acid, charcoal powder, sodium phytate | Yes | Once a week |
| Damage Shield pH Protective Shampoo | Everyday gentle wash | pH 4.5 to 5.5, panthenol, glycerin | Yes | Every wash |
| Damage Shield Protective Conditioner | Protection and softness on non-mask days | Ceramide NP, almond oil, jojoba oil | Yes | Non-mask wash days |
| FutureIQ Hair Longevity Serum | Shedding, early grays, scalp aging | Palmitoyl dipeptide-52, palmitoyl tetrapeptide-20 amide, niacinamide, zinc | Not on the list | Nightly |
If you’re only getting one, get the mask. It’s the product the whole brand is built on and it’s the one with the peptide doing the heavy lifting. The detox shampoo would be my second, especially if you use a lot of styling product or live somewhere with hard water. The Damage Shield pair is nice to have, not need to have. FutureIQ I’d treat as its own separate decision, because it’s doing a different job with different ingredients.
Can you use K18 on human hair wigs and toppers?
I’ve worn wigs and toppers for over twenty years, so this is the bit I cared about most. K18 answer it themselves on their UK blog. They say human hair extensions, pieces and wigs go through all the same damage as the hair on your head, and that the mask handles it. Note the word human, though. Everything K18 say is about human hair.
If you’ve got a human hair topper that’s been colored or heat styled to death, the mask is the one to look at, and it slots straight into a human hair topper care routine. Synthetic pieces are a different thing entirely (I’ve got a whole post on reviving a synthetic wig or topper for those).
K18 FAQs
Do you use conditioner before K18?
No. Shampoo, skip conditioner, towel dry, then apply the mask. K18’s directions are clear on that. The Damage Shield conditioner is for the washes where you’re not using the mask.
How long do you leave K18 in?
Four minutes, then style as normal. You don’t rinse it out at all.
Does K18 help with hair loss?
The mask and shampoos are about damage, not hair loss. FutureIQ is the one K18 market for shedding, and its results come from K18’s own study. If you’re losing a lot of hair, see a doctor first.
Is there a K18 UK website?
Yes, k18hair.co.uk is a separate UK store that charges in pounds. The .com site is the US store in dollars. That’s why I link UK readers to Sephora UK and Space NK, and US readers to K18 direct and Sephora US.
Where to buy K18 in the UK and US
The UK and US are two different shops for K18, so here’s everything in one place.
- Leave-In Molecular Repair Hair Mask: UK at Sephora UK, US at K18 or Sephora US
- Peptide Prep Detox Shampoo: UK at Sephora UK, US at K18 or Sephora US
- Damage Shield pH Protective Shampoo: UK at Sephora UK, US at K18 or Sephora US
- Damage Shield Protective Conditioner: UK at Sephora UK, US at K18 or Sephora US
- FutureIQ Hair Longevity Serum: UK at Space NK or Sephora UK, US at K18 or Sephora US
Ingredient lists change, so always check the box you get. And if seb derm is your thing too, my Lilyeve Scalp:Turn review goes through another scalp product ingredient by ingredient.
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