Mr Cameron's centre parting was not deliberate, he said.
David Cameron has revealed his much commented upon centre-parting at last week's prime minister's questions was the result of wearing a bike helmet.
Mr Cameron, who normally parts his hair to one side, had a new look for the clash with Gordon Brown on Wednesday.
"All that happened is I got on my bicycle, put on a cycle helmet for once, because I'm always being told to... and something went a bit wrong."
He told GMTV "it's amazing how much can be written" about "these things".
During the good humoured exchange at 0720 BST the show's presenter Fiona Phillips said his hair looked "very fetching".
The Conservative leader laughed and said: "I just get in the shower in the morning, and try and get dressed and get to the studio on time."