Peaches Geldof has dismissed reports that she uses heroin after being seen at the Vivienne Westwood fashion party on Wednesday (September 7) with marks on her arms.

Geldof stated: "I’m not on drugs. If people feel the need to validate my weight loss by saying I’m on drugs then shame on them.

“I’ve changed my diet and the way I live. That’s it. The marks on my arms have been there since ­childhood. Check any picture – it’s caused by a skin condition called ­psoriasis.”

Speaking about her slim appearance, Geldof revealed that it's not due to any crash diet but that she is naturally thin like her mother and, as soon as she started eating healthily again, the weight dropped off again

The 22-year-old continued: “The truth is I just didn’t want to treat my body badly ­anymore. I got avian flu and that kick-started the change. I was never fat – it was just the fact that my diet was so ­unhealthy.”

Geldof's mother, Paula Yates died of a heroin overdose in 2000.

Watch news coverage of Peaches Geldof launch her shake at 'Millions Of Shakes', below: