Many reasons as nutritional deficiency,
thyroid problem,harmonal imbalance,
diabetes,hypertension,depression, any long-term debilitating disease.,chemotherapy.......
Get checked for ur basic general symptomsand their specific treatment.
Then specific treatment for hair can be planned.like ayurvedic hair oils,shampoos.,or even oral medicines.
As of now u can use hibiscus,curryleaves,aloevera,amla,methiseeds,brahmi in ur hairoil and for hairpack for washing.
Internally u can take Shatavari gulam two tsf twice a day before food.
Ksheerabala101 cap one twice a day in empty stomach .
If ur having any other underlying disease symptoms please consult.