Why avoid milk products?

The reason that milk products cause acne is because milk contains hormones that "turn on" oil glands. The cows that give the milk are pregnant and milking most of their lives. These hormones are not injected into the cows - they are natural hormones that cows make during every "menstrual" cycle, but during pregnancy these hormones are produced continuously at high levels and so are found in all cows' milk.

In fact – and I’m not exaggerating here – removing milk and dairy products from your diet is probably the absolute, honest-to-goodness most effective thing you can do to clear up your skin.

http://www.acnemilk.com/the_no_milk_acne_diet