The 'Shame' actor suffered with bad hair and skin when he was a teenager and never imagined he would end up as a sex symbol.
He told the latest edition of ELLE UK magazine: "I've never really thought of myself as good looking. I think of myself as, you know, alright.
"I used to have bad acne as a teenager, so all of this is a bonus now, the fact that I don't have pimples any more.
"And my hair was also, you know, unfortunate. I had really long hair. I mean, I tied it back most of the time, but I had all these frizzy bits coming off the top."
Michael - who claimed he was flattered to be named the eighth sexiest male movie star worldwide in a poll earlier this year - has previously said he knows a lot of girls only talk to him because he is famous.
He explained: "You become a lot more successful in terms of, like, talking to a girl. She's all of a sudden more interested in me. I know that three years ago, she would've walked away after two sentences left my mouth.
"I remember I was sitting at this table and I was talking to this girl. I was like, 'God, I am so boring right now.' But she was like, 'That's so interesting!' I was like, 'You know what? Five years ago, this would not have been interesting to you.' "