Myth or Must: Do You Really Need to Switch Up Your Shampoo?

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So, you found a shampoo that makes your hair feel amazing. You use it like a fiend for a solid three weeks and feel like you've finally mastered movie-star hair. But then, week four hits, and you'd swear someone switched out the formula: Your strands definitely don't have the same post-shampoo oomph that they did on day one.

We spoke to hairstylists, dermatologists, and even a cosmetic chemist who all agree: You're not going crazy. "The cumulative nature of the shampoo could be changing the way your hair responds," says cosmetic chemist Ni'Kita Wilson. Matrix SoColor Celebrity Stylist Nick Stenson has seen it happen IRL: "For example, if you're using a protein shampoo for several months, the protein can then build up on the hair causing it to need more moisture. So at that point, your needs have changed and you'd be served better by a different formula."

"Lifestyle needs to be factored in as well," adds Laurie Daniel, colorist at New York City's Marie Robinson Salon. "The same everyday shampoo will not be as effective on three-day old gym hair that's full of product and dry shampoo." That's why Daniel tells her clients to approach their shampoo like a wardrobe: Keep a range of formulas on hand, and choose the one you used based upon the current state of your strands. Mystery solved.