Believe it or not, it's the water you're washing your hair with — more specifically, the copper in your water — that can cause damage. "Often, when people think, 'Oh, the sulfates in that product caused my color to change,' they really didn't," Wilkerson explained. "It's really actually due to the level of copper that the hair is absorbing — especially if somebody washes their hair frequently." Copper can change your hair hue, regardless of whether it's processed.
Don't think that you're safe from color fade even if you only shampoo once a week! Dyed hair is especially porous. Consider this: when you change your mane shade, you're lifting the cuticle, allowing the formula to penetrate the cortex (center) of the strand. After, your cuticles are still lifted, allowing copper in your water to get into the cortex. "When you dye your hair again," Wilkerson added, "that chemistry happens a lot sooner and the color washes out a lot faster."