I agree about clean skin and good quality sunscreen. Face cleaner appropriate for your skin type will help a lot...

Really unsure about the dairy thing. I eat a lot of low-fat dairy products (1%) and have about 2 near-zits a year.

I'd suspect the hormones of making things worse, too, and, if you have problems with your forehead skin, the contact zone between the skin and helmet. Make sure you cleanup when you take the helmet off... I have started wondering how I can clean up the padding of my helmet (it can't be taken off) for it's really absorbing a lot of sweat.