I regularly exercise, i even have around 10% body fat. i eat good, however, i will sometimes eat a lot of sweets (cookies, cake, etc). can it harm me?

Depends on how much: Sugar is considered a poison by many but a famous saying is "the poison is in the dose." if you eat healthy most of the time ; exercise, occasional sweets in moderation may not be terrible, but "a lot of sweets" isn't healthy (but again, not too bad if only on rare occasions). Sweets cause more harm on an empty stomach, less harm when in small amounts after a good meal. See http://nyti.Ms/15xi2o8.