Rihanna admits she has an "ugly week" once a month.

The 'Russian Roulette' singer - who is regularly voted one of the world's sexiest women - says she often dislikes the way she looks and can be quite harsh on herself.

She said: "I have an ugly day every month; pimples on my face, I'm fat and in a bad mood. It's more like an ugly week!"

Despite occasionally feeling overweight, the 22-year-old beauty admits she works hard to maintain her stunning figure.

She said: "I've been working out a lot and I eat pretty boring - boiled egg, fruit, tons of water and some chicken. Well, this week I've eaten some other things but really small portions. I hate vegetables. I hate anything healthy, but if you want the results you've got to do it. I haven't even been drinking alcohol with dinner since I've been with this diet."

Rihanna recently dyed her hair blonde as says she's enjoying her new look.

She told Insider magazine: "Being blonde is a big deal for me. I loved my black hair, but I wanted something that was different. Having this edgy cut with a pretty blonde was an interesting contrast for me."