Hair Allergy. Hair fall. Problem.

My brother had hair fall for last 4 years. He had a head full of hair in 2010 but after he got some kind of an allegry his hair started to fall off and ever since his hair grows to a very minimum level and starts to fall off again. We visited a lot of top doctors here in dhaka. But the problem still persists. He has hair Allergy which causes his hair to fall off. After a very short level his hair doesn't grow anymore like it did in the past. He has gone bald a lot of times and the growth gets stuck to that minimum level. I'm here for a doctoe suggestion. As I have a plan to come to chennai in September 2016, I hope that someone suggests me the best doctors for hair Allergy in chennai or someone particularly for my brother's particular problem.