"We don't know why, but all dairy really flares acne," said Jaliman in an article featured on MSn's Glo Website (see it here). The article goes on to state that junk food (think donuts, pizza and chips) can also cause acne flare-ups. "High-glycemic foods make your insulin levels jump, which affects skin like another big hormonal level change: PMS," said Jaliman.
Bottom line: if you already have a pimple problem, try to maintain a healthy diet and keep in mind that hormones, overactive oil glands, heredity and dead skin cells that lodge in skin pores are the main causes of acne, according to the Acne Resource Center.
Check out my list of the Best Products for Acne-Prone Skin