Katy Perry says she understands why Britney Spears shaved her head.

The singer raised eyebrows in 2007 by getting rid of all her hair during a reported breakdown.

Speaking in the March issue of Elle, Perry said that she understands why some famous people find it hard to cope in the spotlight.

The US star said: "It is a hundred times harder a dream than the dream that I dreamt when I was nine.

"You think you signed up for one thing, but you automatically sign up for a hundred others. And that is why you see people shaving their f**king heads."

Perry meanwhile performed in front of a TV audience of 114.4 million - the biggest in US history - at the Super Bowl on Sunday (February 1).

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