
I was just flipping through nutritionist Joy Bauer's wonderful new book
Food Cures and saw this little tidbit about the acne / dairy connection.
It seems that the connection between dairy and acne is not the milk fat like I previously thought, but iodine and hormones. Iodine-fortified feed is given to cows since iodine helps fight infections and iodine can cause acne in some people.

Dermatologists found a link between acne and high levels of
iodine, which is found in foods such as shellfish. High levels of iodine are also found in dairy products, because the cows are fed iodine-enriched feed to prevent infection.
When iodine enters the body and mixes into your bloodstream, the excess is secreted through the oil glands, irritating your pores.