In a promising step towards eternal youth, scientists have reversed the ageing process in middle-aged and elderly mice using a cellular 'rejuvenation' technique. 

The California-based experts have shown they can partially reset mice cells to 'more youthful states', using four molecules known as the Yamanaka transcription factors. 

After injecting these molecules into mice of various ages, the animals' kidneys and skin showed promising signs of rejuvenation, while their skin cells had a greater ability to proliferate and were less likely to form permanent scars.  

Researchers say their 'safe' treatment could one day help humans wind back their biological clock, lowering risks of cardiovascular disease and cancer.

According to the findings, a treatment period of seven to 10 months may be required to stave off the unwanted side effects of ageing.  

'The technique is both safe and effective in mice,' said Juan Carlos Izpisua Belmonte, co-corresponding author and a professor at the Salk Institute, San Diego, California.

'We are elated that we can use this approach across the life span to slow down ageing in normal animals. 

'In addition to tackling age-related diseases, this approach may provide the biomedical community with a new tool to restore tissue and organismal health by improving cell function and resilience in different disease situations, such as neurodegenerative diseases.'