Chlorine is commonly assumed to be the culprit behind Kermit-colored hair. But the truth is, another compound designed to keep the pool clean may actually be what’s turning your hair green.

Copper sulfate is often added to swimming pools to combat algae, according to the authors of a 2014 case study about a 15-year-old girl whose blonde hair was turning progressively green. “Copper compounds in the water bind to the protein on the surface of the hair shaft and deposit their color,” the researchers explain. (This can also occur if your home has new copper piping.)

Although blonde hair is the most likely shade to go green, “it happens to other colors also,” says Steve Pullan, a trichologist at the Philip Kingsley hair clinic in New York City. “You just don’t notice it as much.” As a hair scientist, he sees green-haired goddesses all summer long — and has noticed a trend among these clients: They’ve often bleached their tresses.

“Even natural hair can become green,” Pullan tells Yahoo Health. But coloring your hair — especially when bleach is involved — makes the shaft of each strand more porous, allowing your locks to absorb the pool chemicals more easily. In fact, in a study called “The Green Hair Problem,” conducted way back in 1979, researchers found that hair treated with peroxide or damaged by the sun was more likely to suck up copper.

Read Yahoo! Health

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