Hair serums aren't just another step in the routine, they're built to work harder than almost anything else you put on your hair. Because they're leave-in and concentrated rather than rinsed out after a couple of minutes like a shampoo or mask, their active ingredients get far longer contact time with hair and scalp. That's exactly why L'Oréal Professionnel, Kérastase, Matrix, Redken, Biolage and Pureology, all part of L'Oréal Group's Professional Products Division, each put their most targeted actives into serum form: bond repair, scalp density, anti-frizz, colour protection and overnight repair. Here's what each brand's formula is actually built to solve.
Why Leave-In Serums Work Harder Than a Rinse-Out Product
A shampoo or conditioner sits on hair for a couple of minutes before it's washed away, which limits how much of an active ingredient can actually work before it's rinsed straight down the drain. A serum skips that limitation entirely: it's applied and left on, giving actives hours, or in the case of an overnight serum, a full night, to keep working. That's why the ingredients brands treat as their most valuable, bond-repair peptides, anti-hair-fall actives, colour-protecting antioxidants, tend to show up in serum form rather than in a rinse-out formula.
That doesn't mean a serum is automatically "better" than a mask or conditioner, a well-formulated rinse-out product can still outperform a poorly made serum. But when it comes to concentrated actives getting a genuinely longer window to work, serums carry a real efficacy advantage that a wash-out product can't match. Across the six ranges below, that advantage gets pointed at six different concerns: bond and structural repair (Matrix, Redken, Pureology, L'Oréal Professionnel), all-over shine (Kérastase), and scalp health and density (Biolage).
L'Oréal Professionnel: Absolut Repair Oil, For Sensitised, Damaged Lengths
Absolut Repair Oil is L'Oréal Professionnel's leave-in treatment oil for hair that's lost strength through colour, heat or chemical services. It's designed to bring dull, sensitised strands back to life without weighing hair down, making it a straightforward daily add-on rather than a once-a-week treatment. If your hair feels rough or brittle to the touch more than it feels dry on the surface, this is the more targeted pick over a straight shine oil.
Kérastase: Elixir Ultime, For All-Over Shine
Elixir Ultime is Kérastase's signature oil-serum, built around a blend of precious oils and positioned as the brand's "iconic regimen for extremely shiny hair." It's less about repairing damage and more about finishing, smoothing the cuticle and reflecting light for that glassy, salon-fresh look immediately after application. It works on more hair types than a repair-specific serum since shine, rather than damage level, is the target.
Matrix: Instacure Build-A-Bond Billion Bond Oil, For Fast Bond Repair
Instacure Build-A-Bond Billion Bond Oil is Matrix's newest serum, a fast-acting leave-in built around a claimed one billion bonds per drop to instantly strengthen hair. It's aimed at anyone who wants a repair-first, rather than shine-first, result, particularly hair that's had recent colour or lightening work and needs bond-level reinforcement rather than a surface gloss.
Redken: Acidic Bonding 24/7 Night & Day Serum, For Overnight Repair
Acidic Bonding 24/7 Night & Day Serum is Redken's first-ever bonding serum, designed to repair daily damage while you sleep as well as protect through the day. It's built for damaged and processed hair specifically, and its point of difference is the overnight angle: most serums are a pre-styling step, this one is designed to keep working long after you've gone to bed.
Biolage: Full Rescue Invigorating Scalp Serum, For Thinning Hair From the Root
Full Rescue Invigorating Scalp Serum is Biolage's answer to a completely different problem: root-level density rather than length-level shine or repair. Formulated with rosemary oil and niacinamide, it's built to strengthen thinning hair by improving the health of the scalp it grows from, making it the one serum on this list that's applied to skin rather than hair fibre.
Expert Tip: Hairhouse stylists recommend matching the serum to the actual problem rather than the price tag, a shine serum like Elixir Ultime won't fix bond damage, and a bond-repair oil won't add root density. If you're not sure which concern is doing the most damage to your hair right now, ask in-store before committing to a routine.
Pureology: Strength Cure Dream Healer Serum, For Fragile, Over-Processed Hair
Strength Cure Dream Healer Serum is Pureology's lightweight leave-in treatment for fragile, overworked strands, built to care for damaged, colour-treated hair without the heaviness of a rinse-out mask. It's positioned closer to Redken and Matrix's repair-first serums than Kérastase's shine-first one, but with Pureology's usual sulfate-free, colour-safe formulation underneath.
So Which One Should You Actually Buy?
Start with the problem, not the brand. Repair-first hair (recent colour, lightening, heat damage) points to Matrix Instacure, Redken Acidic Bonding 24/7, Pureology Strength Cure or L'Oréal Professionnel Absolut Repair, all four are built around strengthening compromised hair fibre. Shine-first hair, healthy but wanting that glassy finish, points to Kérastase Elixir Ultime. And if the real issue is at the root rather than the lengths, thinning, fine regrowth, a tired-feeling scalp, Biolage's Full Rescue Scalp Serum is solving a different problem entirely and is worth adding alongside whichever length-focused serum you choose.
Frequently Asked Questions
Are all these serums interchangeable?
Not really. Each is built around a different core problem, bond repair, shine, or scalp health, so picking based on your specific hair concern will get better results than picking on price or brand recognition alone.
Can I use a hair serum every day?
Most leave-in serums, including all six featured here, are designed for regular or daily use. The exception is a more intensive treatment-style product, which is usually better suited to a few times a week rather than daily.
What's the difference between a hair oil and a hair serum?
The terms are often used interchangeably in professional haircare. Both are typically leave-in, lightweight formulas applied to damp or dry hair, the main difference tends to be texture and whether the formula leans more oil-based or water-based.
Do I need a scalp serum as well as a hair serum?
Only if scalp health or thinning is a specific concern. A hair serum targets the strands themselves, while a scalp serum like Biolage's Full Rescue works on the skin the hair grows from, they solve different problems and can be used together.
Why do L'Oréal Professionnel, Kérastase, Matrix, Redken, Biolage and Pureology all make such different serums if they're the same parent company?
Each brand within L'Oréal Group's Professional Products Division is positioned around a distinct hair concern and price tier, so rather than competing with near-identical products, their hero serums are deliberately built to solve different problems.
Choose Your Serum, By Concern
L'Oréal Professionnel
Absolut Repair Oil 90ml – repair oil for damaged, sensitised hair
Serie Expert Metal Detox Oil 50ml – anti-deposit protector oil for colour-treated hair
Serioxyl Advanced Denser Hair Serum 90ml – daily scalp serum for hair density
Vitamino Color Spectrum Glass Shine 50ml – glass-shine leave-in serum for colour-treated hair
Keratin Alpha Sleek Serum 50ml – smoothing leave-in serum
Pro Longer Liquid Concentrate 15ml – pre-shampoo thickening treatment for long hair
Scalp Advanced Anti-Oily Spray 90ml – anti-oiliness scalp serum
Kérastase
Elixir Ultime 75ml – signature shine oil-serum, also available as a 30ml
Blond Absolu Cicanuit Night Serum 90ml – overnight serum for bleached and blonde hair
Genesis Serum Anti-Chute Fortifiant 90ml – leave-in scalp serum for hair prone to falling
Nutritive Nutri-Supplement Split Ends Serum 50ml – sealing serum for dry hair with split ends
Nutritive Nutri-Supplement Scalp Serum 90ml – moisturising serum for dry scalps
Nutritive 8H Magic Night Serum 90ml – overnight nutrition serum for dry hair
Symbiose Intensive Anti-Dandruff Cellular Night Serum 90ml – overnight anti-dandruff scalp serum
Première Huile Gloss Réparatrice 30ml – concentrated leave-in repair oil
Chronologiste L'Huile de Parfum 75ml – fragranced hair oil
Matrix
Instacure Build-A-Bond Billion Bond Oil 50ml – fast-acting bond repair oil
A Curl Can Dream Oil 131ml – lightweight nourishing oil for curls
Total Results Food For Soft Oil 50ml – hydrating multi-use oil serum
Redken
Acidic Bonding 24/7 Night & Day Serum 100ml – bonding serum for damage repair, day and night
Naked Gloss Lightweight Shine Oil 100ml – featherlight, clinically tested shine oil
Frizz Dismiss Instant Deflate 125ml – anti-frizz oil-in-serum
Frizz Dismiss Anti Static Oil 125ml – lightweight anti-static, anti-frizz oil
Biolage
Full Rescue Invigorating Scalp Serum 50ml – scalp serum for thinning hair
Scalp Sync Oil Balancing Serum 50ml – purifying serum for oily scalps
All In One Multi-Benefit Oil 100ml – lightweight multi-benefit styling oil
Pureology
Strength Cure Dream Healer Serum 100ml – leave-in serum for fragile, over-processed hair
Smooth Perfection Smoothing Serum 150ml – anti-frizz smoothing serum for colour-treated hair
Smooth Perfection Smoothing Lotion 195ml – lightweight smoothing lotion-serum for frizz control
Explore the full range of professional hair serums at Hairhouse, and a Hairhouse stylist can help match the right one, or combination, to your specific hair and scalp concern in-store.