Katy Perry gets turned off by men with bad breath.

The 'Hot N Cold' singer - who is in an on-off relationship with Gym Class Heroes rapper Travis McCoy - would never date a guy who doesn't keep his mouth clean.

She wrote on her Twitter page: "I mean, ladies, how many times did u think that guy was hot but just couldn't deal w/ his breathe? Sense of smell is most important! Agree?

"Some1 next to me has a bad case of halitosis and won't stop talking. I can't breathe. Don't know him but wonder if anyone's eva told him?

"R u the type of friend that wouldn't tell ur friend if they had something stuck in their teeth? What bout bad breath? Wouldn't u wanna know (sic)?"

Meanwhile, Katy has revealed she wants to be as big a star as Gwen Stefani.

The 24-year-old brunette has nothing but admiration for Gwen, 39, because she has had so many years of success in the music business, firstly with her recently reformed band No Doubt.

In a posting on Twitter, she wrote: "When I grow up I want to be just like Gwen Stefani. It's not a race it's a marathon. I keep telling myself this. Think of the big picture. Well the music industry doesn't let u grow anymore. Everything has 2B now, so immediate. Like Gwen - that is 15 years in the making. I can't wait to make magic like that in 15 yrs, I just don't know if people will wait for people to grow like they used too.

"Music is not fast food. It should change and grow and not be such competition of who's on top or not. We all want our musicians to b of Beyonce/Madonna level from the get go when we forget those amazing girls have been doing it for 15-25 years (sic)."