The 23-year-old musician, who plays Alex, a hardened soldier in the Christopher Nolan-directed movie, recounted his experience of chopping off his famous long hair, reported E! News.
"(I didn't) really think about it... It kind of went without saying... I was very excited to be getting to the sets and being involved and working on (the film)," Styles said.
"It was a little breezy behind the ears, which was nice," Styles joked.
"Dunkirk" premieres in theatres on July 21.