This is a public forum Balraj & am apologetic that you seem to have addressed it to a prasad but am taking the liberty of answering.
from time immemorial have been pulling their hair out to answer this question!
Genetic predisposition eg the white forelock of the late Mrs. Indira Gandhi is a major factor that one can allude to.
Chemical damage to the skin & hair predispose to this as does the presence of a skin disease called Vitiligo
or some gentic disorders like piebaldism
The treatment is the supplementation of nutrients to the hair follicles to help promote growth of hair,. Autologous stem cell
injections have in some circles discussed to be beneficial.
For best results, yes do consult with a dermatologist in person.
Cheers & Good Luck!
Dr Praveen Rodrigues MD
Vikram Hospital, Bangalore, India