Oil glands are all over the face. There's usually no particular reason why acne chooses, say, the forehead versus the shin. Local factors like sports equipment and sweaty headbands occasionally are a factor, but most of the time they're not. Food is very unlikely to be related. My advice is to consult a skin specialist about this annoying but actually rather common problem of post-adolescent acne. Topical and oral treatments are available and effective.