Acne is caused by an over working oil gland. When hormones are over active in teens, adults during monthly menstrual cycles, puberty,and things likemenopause or simply clogged pores (blackheads)with trapped sebum (oil).
A breakout or flareup can be caused by a number of things so eat right. If you want to stop a acne breakout don't touch your face with dirty hands, don't pop pimples if you don't know how, and keep your face clean and moisturized.
FYI: A blackhead is a whitehead that is oxidized.(exposed to air).