The Scientist: Arun Nandagiri, founder of Bria Research Labs, a hair care product development and testing facility in Libertyville, Ill.

The Answer: Women who dye their hair have two main concerns to address: maintaining their color and battling damage. Shampoos for color-treated hair are formulated with these goals in mind, though they’re neither a magic bullet nor the only option.

Permanent hair color causes damage. Period. Lighten your locks? Then you can expect your hair to fare even worse. Specially targeted shampoos for color-treated hair are typically milder than other formulas and include extra conditioners to help do damage control.

They also help slow the rate of fading. Among all the reasons for color fade, including sun exposure, chlorine and other chemical treatments, shampooing is always near the top of the list. In fact, even water alone strips hair of its hue. Traditional shampoos with sulfates cause the cuticle layers of the hair to swell, which lets color leach out more easily. (A note to gingers: Red dye molecules are small and escape especially fast.)

So, is it enough to just buy a sulfate-free shampoo and call it a day? Probably, but you may have to do a little extra legwork. For one, sulfate-free shampoos don’t always clean as well—especially if you don’t wash your hair often—so you might find yourself rinsing and repeating each time. And since your hair is already in the damage zone by virtue of being color-treated, you should use a good daily conditioner and deep condition at least once a week.

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