To understand hair loss, think of your scalp as consisting of thouands of hair follicles. Each normal hair follicle houses 3 or 4 strands of hair.
With balding, the hair follicle shrinks, so that the number of hair strands that are able to be accomodate become reduced to 1 or even zero! New strands of hair that grow become thinner in texture as compared to their predecessors. Eventually, the hair follicle will shrink until it becomes nothing more than just a bald piece of skin!
I have undergo scalp checks before at some trichologist centre and the scan that reveals my hair condition attest to that described above as explained by the trichologist.