It sounds like an urban legend, but it isn’t. Too much time in a swimming pool really can turn your hair green. What’s more, chlorine isn’t the only reason. Why hair turns green in swimming pool?
Why does chlorine turn blonde hair green? Black, brown or blonde hair can all take on a greenish tint after time in a swimming pool. The green is hard to see on people with dark hair — but it can be noticeable if your hair is light-colored. And it’s not chlorine that turns hair green. Instead, it’s the presence of certain metals, especially copper.
People have used powerful scanning electron microscopes to make detailed topographic maps of the surface of green hair. Normal hair is covered with a hard, scaly, outer shell called a cuticle. But it’s been found, in case studies of green hair, that the cuticle is often damaged. There’s supposed to be a hard surface around each strand of hair. If that surface is missing or heavily cracked, it might make it easier for the copper compounds to grab onto the hair.
If you swim a lot and have this problem, you can try putting conditioner on your hair — then a tight swim cap — before you go in the water. And once you have green hair, what can you do? The green color might wash away in the shower. But if it sticks around, there are special shampoos that can help.