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Matthew McConaughey has lost one of his sexiest attributes: his full head of curly blond hair!

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The 42-year-old actor stepped out in Beverly Hills, Calif., on Tuesday wearing a baseball cap concealing his newly shaved head. McConaughey, who was dressed head-to-toe in J.K. Livin apparel, was all smiles before beginning his workout at L'Ermitage Hotel.

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No word yet on why McConaughey ditched his signature hairstyle, as the actor was photographed with a full head of hair while shooting "Thunder Run" in Los Angeles on Saturday.

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McConaughey isn't the only star to shave his head in 2011: Jake Gyllenhaal and Matt Damon both lopped off their locks for film roles earlier this year.

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