Compared

Olaplex N°.3 Plus vs N°.4

N°.3 repairs; N°.4 keeps what was repaired. The treatment is a concentrated dose worked through wet hair before shampooing — the directions on the product say roots to ends, three minutes, then rinse and follow with the shampoo — and it is the one that rebuilds the bonds bleach and heat have broken. The shampoo carries the same chemistry at a far lower dose and rinses off in a normal wash — it maintains, and it cannot do the rebuilding on its own. Buying the shampoo instead of the treatment is the usual reason people say Olaplex did nothing for them. Buying the treatment and washing it out with a stripping shampoo is the other.

Olaplex

N°.3 Plus complete repair treatment

Hair that is already damaged — bleached, highlighted, or heat-styled to the point of snapping

Pros

The concentrated dose, worked through wet hair from roots to ends before the shampoo, which is what actually rebuilds bonds
Used before shampooing, so it slots into a wash you were doing anyway
One bottle lasts months at once or twice a week

Cons

It is a pre-wash treatment, not a conditioner — it still has to be washed out
It is the step people skip when they are in a hurry, which is why it sometimes seems not to work
Does nothing for the days between treatments; that is the shampoo's job
1,145 ratings at 4.5 -- Plus is a new formulation, and the evidence behind it is thin next to the original N°.3 it replaces, at 135,550

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Olaplex

N°.4 Bond Maintenance strengthening shampoo

Anyone maintaining repaired hair, or colour-treated hair that is not yet damaged

Pros

The step you already repeat two or three times a week, doing something while it is there
Sulphate-free and colour-safe, which is the pairing that matters on treated hair
78,544 ratings at 4.6 -- a real volume of evidence behind it

Cons

Ninety seconds of contact at a lower dose — maintenance, not repair
Rich enough to weigh down fine hair, which is why the house sells a separate fine version
Replacing the treatment with it is the commonest disappointment with this brand

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Side by side

	Olaplex	Olaplex
What it does	Rebuilds broken bonds.	Holds what was rebuilt.
When	Before the wash, on wet hair.	The wash itself.
Contact time	Three minutes, then rinse.	A normal wash.
How often	Once or twice a week.	Every wash.
On undamaged hair	Little to do.	Worth it on colour.
If you buy one	This one, if hair is breaking.	This one, if it is not.

Everything above is about what these products are, not about tests we ran — we do not test products, and we would rather say so than imply otherwise. Prices live on Amazon, where they change hourly, so we never quote one.

The numbers are a sequence, not a ranking

N°.3 is not a lesser N°.4 and neither is a lesser N°.7. They are steps: treatment, wash, condition, style. A higher number is later in the routine rather than stronger, which is not obvious from a shelf of identically-branded white bottles and is the single most common misreading of this range.

Read the bottle, not the internet

The directions printed on the product are: in the shower, apply generously to wet hair from roots to ends, leave three minutes, rinse, then follow with the shampoo and conditioner. Worth saying because the brand's own blog words it differently -- damp rather than wet, mid-lengths to ends -- and second-hand versions vary more than that again. Where two of the maker's surfaces disagree, this page follows the one printed with the product. An earlier draft of this page said dry hair and ten minutes, which is neither.

What neither of them is

Bond builders repair the internal structure. They do not seal a cuticle, add slip, or protect against heat — which is why the conditioner and the oil exist beside them. Hair that feels rough after a treatment has not failed to repair; it has been repaired and not conditioned.

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