It's the question I get asked most behind the chair: "Should I be using K18 or Olaplex?" Both are repair treatments with a cult following, both cost more than your average mask, and both promise healthier hair. But they don't work the same way, and they're not built for the exact same problems.
Here's how I explain the difference to my clients, and how to choose the right one for your hair.
The short answer
- Choose Olaplex if your hair has been lightened, bleached or chemically processed and feels weak, stretchy or snaps easily. Olaplex is built around rebuilding the bonds that chemical services break.
- Choose K18 if your hair feels dry, rough, frizzy or "fried" from heat styling, colour or general wear and tear, and you want a quick leave-in that restores softness and bounce.
- Use both if you're a heavily lightened blonde or you colour often. They work differently, so they can sit in the same routine.
How Olaplex works
Hair gets its strength from bonds inside the strand, including disulfide bonds. Bleach, colour, perms and even heat break those bonds, which is why processed hair can feel gummy when wet and snap when you brush it.
Olaplex's patented bond-building technology works to relink those broken bonds. That's why salons use it during lightening services, and why the at-home system is so popular with blondes.
The at-home routine I recommend:
- Nº.0 Intensive Bond Building Treatment as a primer, followed by
- Nº.3PLUS Complete Repair Treatment before you shampoo, about once a week
- Nº.4 Shampoo and Nº.5 Conditioner to keep things strong between treatments
- Nº.7 Bonding Oil on the ends for shine and heat protection
How K18 works
K18 takes a different approach. Its K18PEPTIDE is a bioactive peptide designed to reach inside the hair and help repair the keratin structure that gives hair its strength and elasticity. The result clients notice is hair that feels softer, smoother and more "alive", often after the first use.
The big selling point is convenience: the K18 Leave-In Molecular Repair Hair Mask goes on towel-dried hair after shampooing, you wait four minutes, and you style as normal. No rinsing.
Two tips that make a big difference:
- Skip conditioner the day you use it. Conditioner can coat the hair and get in the way. Shampoo, towel-dry, apply K18, wait, style.
- Less is more. A small amount goes a long way. Using too much won't give you better results, just heavier hair.
To keep results going, pair it with the Damage Shield Shampoo and Conditioner, and finish with the Molecular Repair Hair Oil.
K18 vs Olaplex at a glance
| Olaplex | K18 | |
|---|---|---|
| Best for | Bleached, lightened and chemically processed hair | Dry, rough, heat-damaged or colour-treated hair |
| How it works | Relinks broken bonds inside the hair | Peptide that helps repair the keratin structure |
| Main treatment | Nº.3PLUS, applied before shampoo | Leave-In Mask, applied after shampoo |
| Rinse out? | Yes | No |
| How it feels | Stronger, less breakage | Softer, smoother, bouncier |
Can you use K18 and Olaplex together?
Yes. Because they repair hair in different ways, a lot of my blonde clients use both. A simple way to combine them:
- Once a week, use Olaplex Nº.3PLUS before you shampoo.
- Shampoo (and skip conditioner).
- Towel-dry, apply K18 Leave-In Mask, wait four minutes, then style.
On your other wash days, stick to a gentle bond-building shampoo and conditioner from either line.
My honest take
If you've just had a big lightening service, start with Olaplex. If your hair isn't breaking but feels dry, dull or frizzy, start with K18. And if you're not sure which camp you're in, send us a message. Tell us what your hair has been through and I'll point you in the right direction.