But is it hormones and "bioactive molecules," as a study in the Journal of the American Academy of Dermatology suggested, or is there something else?
University at Buffalo dermatologist Harvey Arbesman, M.D., says there could be something else: Iodine.
Arbesman, a UB clinical assistant professor of dermatology and social and preventive medicine, details his reasoning in a letter published in the "Notes and Comments" section of the current (December) issue of the journal.
"It has been well-established since the 1960s that iodine intake can exacerbate acne," said Arbesman. "Nevertheless, various studies have shown there is still a significant level of iodine in milk in several countries, including the U.S., Britain, Denmark, Norway and Italy.
"Farmers give their cows iodine-fortified feed to prevent infection," he noted, "and they use sanitizing iodine solutions on their cows' udders and milking equipment. Consequently, there is lot of iodine in dairy products. For that reason, I've advised my acne patients for years to decrease their dairy intake."
Arbesman suggests the connection between acne and dairy products observed in the study could be secondary to the iodine content of the dairy products. "More importantly," he said, "the connection could be a combination of hormones and iodine."
It's important to bring the iodine connection to the fore to encourage the dairy industry to address the issue, Arbesman said. He suggested that future studies on the relationship of milk products and acne should consider the role iodine content may play.