Katy Perry has stripped off to take part in the ALS ice bucket challenge.

A number of celebrities have filmed themselves being dunked in a bucket of ice or icy water to raise awareness for neurodegenerative illness ALS.

Big names Lady Gaga, Taylor Swift and Justin Bieber have all undertaken the challenge, with some also pledging money the cause.

Katy Perry has now joined in the fun and she went one further by doing the challenge in a bikini.

She wrote on Instagram: "Thank you @thestevetisch @aw & @hellogiggles for nominating me for the ALS #theicebucketchallenge I now nominate @madonna (ALSO SORRY THIS IS SO LOUD & ANNOYING)."

At the time of writing, it seems Madonna has yet to accept the challenge.

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Watch Katy Perry getting dunked in ice below: