Experts say that wearing cheap versions of UGG-style boots could cause serious health problems later on in life.
Dr Ian Drysdale is principal of the British College of Osteopathic Medicine and is warning the soft boots don't give feet any support and can cause long term damage to ankles, knees, hips and back.
Official UGG boots cost from around £150 but much cheaper versions are available on the high street and from markets.
UGG Australia says its boots are "made with the finest materials and designed with the utmost care and attention to detail" including "structured heel counters" for "substantial support". The company is urging people to beware of copies.
Newsbeat took 14-year-old Hannah and her £10 knock-offs to meet an expert.