I'm sure there are many causes of why suddenly somebody would flare, such as a girl coming off of a birth control pill. Perhaps, stressful events. It's very difficult to measure, "does stress really make acne flare?" but anecdotally we hear that all the time so it may well be that this is real. Do foods make acne worse? Very controversial. Many studies over many years suggested that food has nothing to do with acne. Although more recently, we have an understanding that for some people, it might. We do have evidence that milk, especially skimmed milk may be an aggravating factor especially for people who have severe acne. We know that individuals who eat lots of fish - it may protect those with moderate to severe acne - it may inhibit the formation of acne. There is some evidence that acne may be flared by high glycemic foods refined sugary foods, the western sort of diet may be a factor in producing acne in the first place. We know that rural non-western cultures have much less acne than we do in the west. So there are these environmental issues that we don't fully understand.