Hey Aarti, it could be due to poor diet or due to air pollution. It could be also due to some hormonal changes. There are many therapies which work for the same, but the best advice would be if you go and visit a dermatologist for the same, They will be able to help you in the best line of treatment, however if you feel oiling your hair, using onion juice, meethi seeds work as good remedies. you can perhaps try them also often.