Hello, you are underweight and that can be cause of malnutrition to hairs. As hairs are malnourished, they become thin and scalp becomes weak. Weak scalp is prone to infection and degeneration, which ultimately leads to dandruff. Please let me know your dietary habits and bowel habits, as this area needs rectification. Till then, you can start with glycyrrhizin and wedelolactone and let me know your feedback.