DNA damage caused by the sun, smoking or an unhealthy lifestyle causes hair to turn grey, a new study has shown.

The research, published by a team of Japanese scientists in the journal Cell, shows that DNA damage to melanocyte stem cells in mice, the cells that produce hair's colour pigment melanin, leads to hair changing colour.

Cancer researcher Tracey Bryan, of Westmead Hospital in Sydney, says scientists have known for some time that DNA damage accelerates ageing.

But she says, "what's novel [in this research] is the role of stem cells in the ageing process."

Migrating stem cells

Bryan says recent research has shown that DNA damage accumulated in stem cells, the basic cells that can transform into specialised cells such as skin, brain or muscle, is most important in ageing.

In healthy hair strands, stem cells migrate to the blub of the hair follicle, gaining the pigment melanin to become melanocytes. The melanocytes then move into the shaft of the hair giving it colour, says Brian.

"What's happening in grey hair is that the stem cells are turning into melanocytes in the wrong location. They never reach the blub or contribute to the hair so the hair goes grey," she says.

Brian says these non-functioning melanocytes are called ectopic cells.

Molecular biologist Brian Morris, of the University of Sydney, says melanocyte stem cells live in niche's inside the blub region of the hair follicle.

He says these areas need to be preserved for hair colour to remain throughout our lives.

"With age, DNA damage takes place through smoking, stress, radiation and as a result good melanocyte cells become depleted, and we see greying of the hair."

Checkpoint malfunction

Morris says the Japanese study also uncovered a stem cell checkpoint, an enzyme called ATM, that can also determine whether stem cells become functioning melanocytes or ectopic cells.

If the checkpoint is damaged it can result in more cells moving into the ectopic phase, he says.

Morris says understanding how cells work and age will lead to new ways of counteracting the ageing mechanisms.

"Everyone's interested in ageing because it's the one thing we have in common," he says.

Bryan believes the study could also have implications for cancer research.

"Cancer and ageing are like the flipside of one coin," she says.

Bryan says DNA damage causes stem cells to age and become cells they're not supposed to be.

"It's thought stem cells are involved in cancer growth. So if we could harness that process and cause cancer cells to age prematurely, it would possibly stop their proliferation."

In the meantime Morris says the natural way to reduce DNA damage and delay the ageing process is to eat well, exercise and avoid smoking, alcohol and too much sun.