In a series of experiments, they have identified a protein called ‘wnt’ found to be vital to the production of colour in hairs.

The breakthrough raises the prospects of drugs, lotions or shampoos that raise levels of wnt – and restore white or grey hair to its natural colour…

Writing in the journal Cell, they show that the protein kick-starts a chain of reactions which lead to stem or ‘mother’ cells in the scalp maturing and producing the pigment that gives hair its colour.

A similar chain of reactions takes place in the human scalp, but the researchers, from New York University’s Langone Medical Centre, have yet to prove that faults in the system turn people’s hair grey.