High-glycaemic foods and dairy have some evidence linking them to acne severity in susceptible individuals. A consistent skincare routine using a mild cleanser twice daily and a non-comedogenic moisturiser is more effective than dietary changes for most teenagers.
Over-washing and harsh scrubs are counterproductive. They strip the skin barrier and trigger more oil production. A basic routine used consistently beats an elaborate one used inconsistently. A dermatologist is worth seeing for moderate to severe cases.