When you're a bottle blonde coming from a super-dark base, preventing your strands from eventually shifting toward orange becomes an ongoing battle. Sure, it can be held off by the countless glosses, color-depositing shampoos and conditioners, and toning products on the market, but the question remains: why does this even happen in the first place? Ripping a page from your high school biology book, Dr. Joe Cincotta, chemist for haircare brand Color Wow, says the answer lies in the melanin found in your hair shaft. "Dark hair has two types of melanin in it, and when it comes in contact with peroxide, the peroxides attack your melanin," he explains. "The melanin for dark hair doesn't immediately go to blonde—it goes to an intermediate red phase, and your natural melanin is broken down." Once your hair gets as light as your stylist sees fit, either a toner or dye is applied over the top, but both do eventually fade as you continue to wash your hair post-appointment.
"As the dye leaves the hair, that partially broken-down melanin comes through," Dr. Cincotta continues. "If you don't take the melanin down until it's completely eliminated, you'll have brassiness under the color or toner that starts to come through after a few weeks." Luckily, there are a few ways to counteract this, or at least, have a less apparent sepia tint until your next salon appointment. To start, you'll want to take a closer look at the ingredient list of products currently in your shower, and swap out anything that has sulfates or alcohol in the mix. According to Gail Federici, founder and CEO of Color Wow, certain ingredients will cause your color to oxidize on the hair surface. "Use a low-density, sulfate-free shampoo to keep your cuticle tight, and look for condditioners that use translucent conditioning agents that won't oxidize once they hit the hair," she says. Additionally, incorporate pigment-infused treatment products into your regime, like those with a slight violet tint, to neutralize the yellow and orange tones that eventually take shape. Though your highlights may not need to be retouched every few weeks (depending on your desired intensity), you may want to visit your stylist for the occasional gloss to keep your color in check, which also results in super-shiny layers.