[YEA] I have had cystic acne for over 15 years, always worsening right before my period. My skin was pretty clear overall except for one or two large cysts on my chin coming or going at all times. Long story short, I found that eliminating dairy has almost completely resolved the problem. I can still have small amounts, like the occasional slice of pizza, but when I let loose on a milkshake, it shows a few days later.
My esthetician told me that the acne profile of cystic zits on the chin and clear skin elsewhere is a good indication that the acne is hormonal. Not everyone has this reaction to dairy, acne can be caused by many things, but it has worked really well for me and a friend of mine. It is quite sad to have to dramatically reduce my dairy consumption, but it's worth it if it works.