What we think
K18's active is a short peptide designed to reconnect broken keratin chains from the inside. That is a different mechanism from Olaplex's disulphide-bond chemistry, and in practice it works faster: four minutes, no rinse, and the hair feels structurally different rather than just coated.
The problem is dosing. The instructions are specific and counter-intuitive, and almost nobody follows them.
How to actually use it
This matters more than any other product on this site:
- Shampoo, then towel-dry. No conditioner first — conditioner blocks the peptide from reaching the hair.
- Damp, not wet. Water dilutes it.
- Four pumps for shoulder-length hair. Not eight. Not a palmful.
- Wait four minutes. Do not rinse. Then style as normal.
Used with conditioner underneath, or on soaking hair, or in double the quantity, it will feel greasy and do less. Every "it made my hair worse" review describes one of those three mistakes.
Price and value
The lowest score on the axis. A 50ml bottle is expensive and, used correctly, lasts around fifteen treatments. Olaplex No.3 costs less per use and gets most of the way there.
Who it is for
Hair that is genuinely damaged — heavy bleach, chemical straightening, daily heat. On mildly dry hair it is money spent on a problem you do not have.
