Hair is not so much damaged by the sun as buried under things. That is the sentence the haircare industry does not say out loud, because it does not lead to selling another bottle but to one treatment done once.

Over the summer, heavy metals from tap water, chlorine from the pool, residues from everyday products and badly fixed colour build up inside the fibre. They do not sit on the surface - they enter the cortex and change how the fibre behaves. The result is hair that becomes resistant to everything applied to it afterwards. The mask does not penetrate. The colour comes out different from what was expected. The shine does not return, however much work goes into it.

Chelation is not another shampoo

Paz Toralba, founder of The Beauty Concept, explains that this is a chemical process in which specific agents bind to the metal ions inside the fibre and neutralise them so they can be rinsed out. Unlike deep-cleansing shampoos that work on the surface, chelation acts from the cortex towards the cuticle - it restores the whole fibre, not just its tip.

"Hair arrives in salons with an accumulated history: chlorine from the pool, minerals from hard water, residue from badly fixed colour. Chelation is what allows everything that comes afterwards to work," Toralba says. That is the key - the treatment is not a finish, it is a start. It opens the door to everything else.

What specifically changes

Colour fixes more precisely and the tone is truer to what was agreed. It lasts longer. Porosity drops, so the fibre is smoother and more compact. It breaks less when combed. The reaction to humidity becomes predictable - the hair does not swell up every time the weather turns. And the shine comes from depth, not from a silicone that will rinse out on the second wash.

September is the month when this makes sense, because by then the summer's bill is complete. The question worth asking yourself before buying your sixth product this year: is the problem that something is missing, or that you already have too much piled on?