Thought I'd weigh in on the acne topic as a doctor. I've seen a lot of Acne - 90% of teenagers get it after all - and it can cause a lot of problems.
Cause - simply put when your gland produce oil (sebum) this can cause local irritation and sometimes lead to blocking pores and trapping bacteria in there. This is why teenagers get it because their hormones cause more sebum production which is directly linked to severity of acne. Not all acne has bacteria involved but the worst cases typically do.

Treatment - this is step wise and theres a huge variety of meds to try so I won't go into too much depth. But typically you start with a topical retinoid / benzoyl peroxide then move up to topical antibiotic then oral antibiotics. If it's very bad specialists might consider laser / isotretinoin usage.

Food relation - this article touches on it nicely. Ultimately unhealthy foods cause you to produce more sebum through a complex mechanism. Anything that can lead to electrolyte imbalances and increased sweating can contribute. On the whole the best evidence based advice is to stay active and eat a healthy, well balanced diet which helps for Many things including acne. Everyone is different so why not try a food diary to see if any particular foods seem to cause you a flare up.
I'll stop talking now :p