Guru Pyaari'o
Is it "baldness", i.e. the thinning of hair resulting in hair loss. You cannot prevent nature but you can slow down the processes with good diet (eats lots of almonds, almond oil in hair, good diet, exercises and live stress free, i.e. Gursikhi Jeevan & Naam Japnaa).
OR
is it alopecia which is when there are odd patches where there is totally no hair and these patches are growing?
Photos of alopecia:
You need to find this out and accordingly get medical advice. If it's alopecia then your better off going to Ayurvedic specialist or Eastern medicine specialists because Western doctors know little about the condition and will probably tell you there is no cure but my dad and a few other people have had Desi treatment for alopecia and it's worked.