Why your colour goes brassy, and what actually stops it

Brass is warmth that was always in your hair coming back to the surface as the deposited tone washes out. Lightening removes pigment in an order — blue first, then red, then yellow — so the warm tones are what is left underneath whatever we put on top.

What genuinely slows it

Cooler water, less of it. Every wash takes a little tone with it, and heat opens the cuticle so it takes more.

A UV filter, if you are outside a lot. Sunlight oxidises the tone faster than shampoo does.

A gloss every six weeks. Not a toner from a box — a gloss done on clean hair, which takes twenty minutes and costs less than a colour correction by a factor of ten.

What does not

Purple shampoo, used daily, on hair that has gone brassy rather than yellow. Purple cancels yellow. Brass is orange. You want blue, and you want it once a week at most, or you will end up flat and grey.