Katy Perry dresses like a 13 year old.

The 'Roar' singer favours bright colours and playful stage costumes by brands like Moschino and Cavalli during her 'Prismatic World Tour' because she still has the same fun-loving sense of style she had when she was a teenage girl.

She said: ''There's a lot of colour in my shows. I have so much fun with it. I'm going to be 30 at the end of this year, but I still feel like a 13 year old. Right now, I'm really obsessed with the Versace early 90s soft-grunge look, but I don't think there should be any rules when it comes to colour.''

Despite being on stage almost every night during her world tour, Katy ensures she does at least 30 minutes of cardio per day.

She explained to Britain's InStyle magazine: ''When I'm on tour, the exercise routine is vigorous. I'll work out every day, and I don't have time for a full hour of exercise, I'll run on the treadmill for 30 minutes. I actually love having that uninterrupted time to listen to new music or my favourite albums, and it feels great to get the blood circulating, too.''

And Katy is so obsessed with her beauty products that she refuses to stay over at friends' houses without them.

She laughed: ''Me and my dancers love playing around with make-up and nails. Going over to casually stay at someone's house is not possible unless they have the same 52 products as me!''