Stem cells producing the wrong kind of hair could be the cause of baldness in men, scientists say.
The American team hope to eventually develop a cream that would get the stem cells to start producing normal hair.
More than half of men over the age of 50 have some degree of baldness and for some, hair loss begins in their 20s, the BBC reports.
By studying men undergoing hair transplants, the scientists at the University of Pensylvania found the problem lies deep within the hair folicles where new hair is made.
They spotted faulty stem cells at work which produce new hair so small it could only be seen under a microscope.
The scientists believe that restoring the functions of these cells could be a way to treat baldness.
Until now it has been unclear what the exact cause of male pattern baldness is, but experts believe the male hormone testosterone is involved and baldness also tends to run in families.