When your color just doesn't look as vibrant and it's time for a touch up, it's probably the fault of oxidation. And blondes aren't the only ones who get brassy. Oxidation can happen to brunettes and redheads, too. "People think it’s the sun that oxidizes, but it’s just the elements: hard water in your faucet, shampoo, conditioner," Kari explained. "Permanent color in general has an expiration date."
At around four weeks when your hair color starts to turn, book a toner or gloss or buildup remover with your salon (and a conditioning treatment, too). At home make sure to use a lavender shampoo like L'Oréal EverPure Blonde Brass Banisher Shampoo ($7). It's not just for blondes! According to Kari, brunettes with ombré hair color and highlights can go brassy before their platinum girlfriends.