When applying too much hest on your hair with heating products that can damage hair shafts. With lack of moisture it can cause brittle hair and potentially hair breakage. Bleaching your hair can also be harmful as youre putting substances that destroy certain cells bacteria etc.
You burned it with your hair dryer. If you've heard it once, you've heard it a thousand times: Heat is not your hair's friend. You broke it with your brush. You broke it trying to save it from heat-styling.
