From Some Time I Was Having Itching On My Head.now

from some time i was having itching on my head.now there is a patch where the hair are finished. i don't understand why this has been happened. from my childhood i am using aavnla hair oil. every alternate day i uses head and shoulder shampoo for the last 20 years. why this has been happened and how i can cure this. myself mukesh shrivastava, from new delhi, india.