Each hair passes through various stages in its lifecycle. Anagen phase is when the hair grows, then comes Catagen phase, Telogen phase is the resting stage and Exogen phase is when the hair falls. Thinning is a sign of slowing hair growth. Hair thinning is not a good sign and implies that hair will fall in the future. Hair thinning can be prevented by taking minoxidil 5% lotion, Finasteride or Dutasteride tablets which improves blood supply but this is not a permanent solution.
Transplant should not be done for hair thinning, it should be done for baldness.