After three months of sun, salt water and chlorine, hair does not need a cut - it needs repair. Or so the hairdressing trade claims. The question is whether a „protein treatment\" means anything concrete, or is just another word that makes a shampoo fifteen euros more expensive.

Rosi Fernández, a hairdresser and salon director in the Madrid district of El Viso, explains the mechanism without any magic. „The proteins we find in hair products are, for example, keratin, collagen and hydrolysed fragments,\" she says. „They stick to the hair's cuticle, fill it in and add shine.\"

That „fill in\" is the key phrase, and she is straight about what follows. When a strand is damaged, its surface becomes irregular and loses part of its protection. Since hair is predominantly keratin - that is, protein - keratin products can latch onto the most damaged and most porous sections and partly smooth them out.

„A kind of film forms, a temporary reinforcement of the strand, which makes the hair feel softer, more resilient and less coarse,\" Fernández explains. But she immediately adds the caveat you rarely hear in an advert: proteins do not permanently repair structurally damaged hair. What they do is improve the appearance and reduce split ends.

That is a distinction worth money. If you are buying a product thinking it will return your hair to the state it was in before three bleachings - no, that does not happen. If you are buying it so your hair looks and feels better until healthy strands grow in - that is realistic, and that is what the product genuinely offers.

Who needs it? According to the hairdresser, mostly hair weakened by chemical treatments, bleaching, or frequent use of straighteners and hairdryers. „If it is more porous, brittle, dull or split, it may need a dose of protein.\"

And here comes the advice no brand will put on a label: do not overdo it. „The ideal is to use them in a balanced way, through specific products or treatments according to the hair's needs, alternating them with hydration so the strand is not overloaded,\" Fernández says. Too much protein makes hair stiff and brittle - exactly the opposite of what it was paid for.

The whole story comes down to one thing: this is makeup for the hair strand, not surgery. Very useful makeup, but makeup. Anyone promising you a permanent repair out of a bottle is selling you something else.