Hi welcome to HCMForum. it is not harmonal defect as the hair in all other areas is normal.
you might be using some steroid
containing cream for fair ness since very long time. if it is
the reason you should stop using it for ever, then you can get back hair after 6months or so.
i advise you to consult a dermatologist
for diagnosis. Besies i advise you some diet recomendations
as take more of green leafy vegetables pulses egg mutton milk carrot fruits