The challenge consists in people dumping ice cold water on their heads and nominating others to do the same.

ALS stands for Amyotrophic Lateral Sclerosis and is also known as "Lou Gehrigh's disease" after the baseball great who was diagnosed with it in 1939. It is a degenerative disease that kills off motor neurons, eventually ending the brain's ability to initiate and control muscles.

The ALS ice bucket campaign has become a global phenomenon and raised $23m. Facebook CEO Mark Zuckerberg, Microsoft founder Bill Gates and football sensation Christiano Ronaldo are also among those who have taken part.

So what is behind the success of this campaign? John Terret reports from New York.  

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