Why Does Swimmer's Hair Turn Green? (It's Not What You Think)

It's widely blamed on chlorine, but the real cause of green swimmer's hair is copper. Most pools contain trace copper, either from algaecide products or corroded pipes, and chlorine's role is oxidising that copper so it binds more easily to hair — especially hair that's already damaged or light in colour.

The real culprit: copper, not chlorine

Copper ions bind to keratin, the protein that makes up hair. Chlorine on its own doesn't turn hair green — but it oxidises copper in the water, which makes it bind to hair more readily. So chlorine is an accessory to the problem, not the direct cause.

Why blonde, grey, and damaged hair show it most

Lighter hair shows any discolouration more visibly, but the bigger factor is damage. Hair that's already been bleached, chemically treated, or sun-damaged has more broken bonds in its structure, making it easier for copper ions to attach. Healthy hair is naturally more resistant.

How to prevent it

A swim cap is the most reliable prevention. On top of that, applying SWIM OIL before swimming adds a protective layer between hair and the water, reducing how much it absorbs during the swim.

How to fix it if it's already green

A chelating shampoo — one that specifically binds to copper ions and lifts them out of hair — is the proven fix, rather than home remedies. For the record: there's no real evidence that tomato sauce or ketchup does anything useful here, despite the popular myth.

FAQ

Is it my shampoo's fault my hair turned green?

No — regular shampoo isn't designed to remove copper specifically, so it won't reliably fix or prevent this.

Does a swim cap fully prevent it?

It significantly reduces exposure, but water still gets in at the edges over a long session — pair it with SWIM OIL for extra protection.