What are the causes of acne (for those that are hard to remove n will go out from the same place again n again)? bacteria or hormone or anything else?

Both: Acne arises from hormonal changes especially in youth and bacteria that are very common and cannot be eradicated permanently. A woman who can take and wants the oral contraceptive pill may find it makes acne remit; otherwise, if there are not a great number of blackheads, benzoyl peroxide (no rx needed) with or without topical Clindamycin (prescription) is a good start.