Scientists hope discovering how the ageing process turns a person's hair grey will help them treat skin cancer.
Scientists believe a pigment cell holds the key to premature greying
Greying is linked to pigment cells called melanocytes, Science reports.
Hair loses its colour and turns silver when cells that spawn melanocytes die off, the team from Boston's Dana-Farber Cancer Institute told the journal.
Melanocytes also go awry and multiply uncontrollably in deadly skin cancers so the team hopes the findings could lead to a way to stop tumour growth.
The malfunction occurs in malignant melanoma, the most dangerous form of skin cancer.
Now that they have pinpointed how melanocyte numbers are killed off with ageing, the US scientists hope doctors will one day be able to turn off cancerous melanocytes.
Dr David Fisher and colleagues looked at what was happening in the hair follicles of mice and then humans as they aged.
They traced the loss of hair colour to the gradual dying off of the precursors to melanocytes.
Not only were there fewer numbers of these non-specialised cells, they also began to make more errors.
Some were turning into fully committed melanocytes in the wrong place within the hair follicle where they are useless for colouring the hair.
The team then looked at what would happen if they 'knocked out' a gene in mice that is known to be important for cell survival.
Mice lacking this Bcl2 gene went grey shortly after birth.
The scientists believe the same principle might apply in humans, which would explain why some people - such as TV presenter Philip Schofield - go grey in their 20s, while others keep their dark locks into retirement.
But more importantly, they hope it will point the way to a treatment for melanoma.
Dr Fisher said: "Preventing the greying of hair is not our goal.
"Our goal is to prevent or treat melanoma.
"We would love to identify a signal that would make a melanoma cell stop growing."
Dr Richard Marais, of The Institute of Cancer Research, said: "This work is exciting because it provides us with a
better understanding of the biology of melanocytes, and will ultimately provide a better understanding of why these cells become dysfunctional and lead to cancer.
"In due course this could provide us with new strategies to treat melanoma."
Consultant dermatologist Dr Andrew Messenger, of the Royal Hallamshire Hospital, Sheffield, said: "We do need new treatments for melanoma.
"The first line treatment is surgical removal. It's a tumour which is not very responsive to chemotherapy or radiotherapy, and it still has a high mortality."