And why it stops growing...
Fri 17 Jun, 2011 11:00 am BST
© Yuri Arcurs - Fotolia.com
Researchers at the New York University Langone Medical Centre think that a breakdown in communication between the stem cells in hair follicles and melanocyte stem cells may be the cause of hair turning grey.
Melanocytes are the pigment producing cells which give hair its colour, while follicle stem cells are responsible for the growth of new hair.
"We have known for decades that hair follicle stem cells and pigment-producing melanocycte cells collaborate to produce coloured hair, but the underlying reasons were unknown," said Dr. Mayumi Ito, who led the study.
The scientists used a mouse model to examine how the follicle cells and melanocytes work together to generate hair growth and produce hair colour.
They identified a signalling pathway - known as Wnt - which follicle cells use to send instructions to, and activate stem cell melanocytes. Once they receive the Wnt signal, the melanocytes start producing pigment which gives hair its colour.
Inhibiting Wnt signalling in hair follicle stem cells inhibited both hair re-growth and prevented melanocyte stem cell activation leading to depigmented or grey hair in mice.
The study findings suggest that manipulating the Wnt signalling pathway may help prevent hair turning grey and even prevent hair thinning.
If scientists managed to achieve this in humans, it would be welcome news to the many men and women of a certain age who spend a small fortune on hair colouring.
The research also provides insight into diseases in which melanocytes are lost, or grow uncontrollably as in the deadly type of skin cancer, melanoma.
The study is published in the journal Cell