Credit: Jason Merritt/; Christopher Polk/Getty

Fun celeb fact: In addition to being young moms, Christina Aguilera and Katie Holmes share the same birthday (Dec. 18). On Sunday the singer turns 31 and the actress/designer will be 33.

And while their styles are dramatically different -- Aguilera is known for her super-sexy, over-the-top looks, Holmes typically goes for chic, high-fashion ensembles -- they've both changed up their hair several times in the last decade.

PHOTOS: Biggest celeb hair makeovers of 2011

Click through to see the stars' hair through the years and tell Us which look you like best on each one!