The Bonds That Hold a Strand Together
The keratin chains in the cortex are joined by several types of bond. The strongest are the disulfide bonds: they determine the shape of the strand and much of its strength.
What breaks them
Bleaching, perming, straightening and any service that alters hair structure works precisely by breaking those bonds. The problem is that some of them do not reform on their own. The mechanisms are covered in detail in our article on chemical damage.
How Plex Products Work
The active molecule links to the broken sulfur groups and holds them together while the chemical process runs. The idea is not to repair already-damaged hair but to prevent some of the damage during the service itself.
Which is where the main misunderstanding starts
A plex product works best used alongside the bleach or colour. Home versions applied weeks after the service have a far more limited effect: the bonds it was meant to protect have already broken.
What the Data Shows
The tensile strength figures quoted in marketing come from trials run by the makers of the respective technologies. They are a useful guide, but they are not independently confirmed and are obtained under controlled laboratory conditions that differ from a salon.
When It Is Worth It
For bleaching, especially several levels at once, for going from dark to blonde, and for hair that has already been processed repeatedly. For a simple colour close to your natural tone, the benefit is considerably smaller.
Salon Service or Home Use
Salon versions are mixed directly into the bleach or colour and work at the moment the bonds are breaking. That is also the moment when they make the most sense.
Home products are lower in concentration and used as maintenance between appointments. They cannot restore bonds that have already broken, but they help hair feel stronger and break less during combing and styling.
How often at home
Once a week is enough for most people. More often does not speed anything up and in some cases leads to stiff, inflexible hair, much like overdoing protein treatments. If hair starts to feel dry and brittle, take a break.
What Plex Cannot Do
It does not permit unlimited lightening. It does not remove the need for a colourist to judge how far a particular head of hair can go. And most importantly: it does not mend split ends, which are a mechanical splitting of the strand and are solved only with scissors.
The realistic expectation is less damage during the service and hair that copes with the chemistry better than it would have otherwise. That is a meaningful benefit, but it is different from repair.
How to Keep the Result
After a lightening service hair stays more porous and more vulnerable. Cooler water when washing, lower heat settings, heat protection every time you style, and a trim every two or three months do more than any additional product.
It also helps to alternate protein and moisture treatments rather than relying on one. There is more in our article on hydrolysed keratin.
A plex product is not a substitute for regular care and does not remove the need to cut damaged ends off. How to maintain the result is covered in our hair care routine.
When It Makes Most Sense
On hair that has been lightened, permed or straightened, meaning where the internal bonds have genuinely been stressed. On natural, unprocessed hair the difference is far less noticeable.
If your hair breaks mainly from mechanical damage during drying and combing, changing your daily care will do more than another treatment.