Illness or stress can prompt hair colour loss
People whose hair has turned white because of illness or extreme stress are being offered hope that scientists may be able to reverse the process.
Researchers from Manchester University and Lubeck University, in Germany, used a molecule to stimulate the pigment responsible for hair colour.
But they said the technique still had to be tested on humans and would not reverse the natural greying process.
However, experts said the development was an encouraging breakthrough.
The research team recreated a naturally-occurring molecule called K(D)PT, which is very similar to the hormones in the body that stimulate the hair pigment melanin.
The researchers took hair follicles from six women aged between 46 and 65 and mimicked two conditions which can turn hair white - a skin disease known as alopecia areata and stress-related disorder telogen effluvium.
They found that, once treated with K(D)PT, the amount of melanin in the follicle increased significantly.
Lead researcher Dr Ralf Paus said the melanin stimulation suggested the technique could be used as an "anti-greying agent".
But he warned it was still early days and it was not known if it could be used to restore hair to its full colour.
Nina Goad, of the British Association of Dermatologists, said: "It's important to note that this is laboratory research and not yet ready for use on patients.
"However, while the research is still at a very early stage, these findings could potentially pave the way for new therapies that restore colour to white hair.
"At the moment, this research only applies to people whose hair has turned white following illness, but this is an important step for such patients."