Miley Cyrus's haircut - blonde, shaved sides - is now one of her trademarks, along with twerking and wearing a bra as a shirt. But Miley's haircut isn't just a style statement; the singer says it changed her life.

Miley Cyrus used Twitter to debut her very short, blonde hair in 2012. As if she finally shed all signs of her "Hannah Montana" past, Miley began to dress more provocatively, showing off the results of her fitness regime. Miley's confidence didn't just extend to her style, it showed in her tweets, her videos, and her interviews. As the lyrics of Miley Cyrus's song "We Can't Stop," says, "it's our party we can do what we want!"

Miley Cyrus may top the list of life-changing hairstyles, but she's not the only one on it. In Hollywood, hair seems to have a profound effect on more than a few careers, just ask Keri Russell.

Television drama "Felicity" was at the height of its popularity in 2000 when things changed at the snip of a pair of scissors! Keri Russell played the college student whose signature look was a generous head of curls. When Keri cut all that hair, just like someone on an adventurous mood would, the result was a decline in ratings.

It's not only the cut, but the hair colour. Emma Stone and Christina Hendricks should know. Emma, a natural blonde, dyed her hair at a bid to get more serious movie roles. "Mad Men" star Christina Hendricks has the same tale to tell. Now, the blonde actress is one of the most recognisable "redheads" in the industry.

For a long time, Michelle Williams was known as "Dawson's Creek's" Jen Lindley. The actress didn't want for work after the series ended and Michelle's personal style seemed on its way to gaining fame. But it wasn't until Michelle Williams's pixie cut in 2010 that the actress truly found a signature look, gaining fashion and hairstyle fans along the way.

Jennifer Aniston's "Rachel," Kate Middleton's half-up half-down style, and Kim Sears's blow-out are some of the most requested looks at hair salons. But there was a time when every woman wanted a "pob," or some version of it. We have Victoria Beckham's angled bob to thank for that. Posh Spice overhauled her image, going from Spice Girl, to Mrs. Beckham, to tastemaker and fashion designer. And she did it all with perfectly groomed hair!

Start the slideshow for Miley Cyrus's haircut and more "life-changing" hairstyles.

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