Hi..dear Brahmisree.,
Thanks for choosing HCM..,
If U want Root cause of Hair loss...U can do these..,
tests...and treat the cause...This is the systemic way..,
to approach the case..,
But The probable causes are...Malnutrtion, Fungal infections of 
scalp.,
Genetic, 
Stress and strain.., other medications.., Worm infesttions and..,
 Chronic debilitated  conditions...ok.,
Now U follow (never mind about cause)..
1) Apply Ketaconazole shampoo...,once in 3 days.,
2) Daily apply 
Minoxidil 5% lotion.,night times.,
3) Tab..Boitin 10 mg daily for 90 days..,
4) Take plenty of vegetables and fresh fruits..,
thanQ