After a thorough review of the literature up until today…
This is what scientists know:
Hormones: Milk contains hormones such as IGF-1 (insulin-like growth factor) and androgen (male hormone) precursors.
Iodine: Milk often contains iodine, largely due to farmers dipping the teats of cows in an iodine solution before milking in order to sterilize. At large doses, iodine can cause what are called acneiform eruptions. Acneiform eruptions look similar to run-of-the-mill acne vulgaris but are different in important ways.
This is what scientists postulate, but don’t know:
Hormones: IGF-1 and androgen precursors in milk could theoretically lead to increased skin cell production, causing pores to become clogged. IGF-1 and androgen precursors could also theoretically lead to increased skin oil production. Since we know that acne does not flourish in low oil environments, perhaps the hormones in milk might help provide an oily fertile ground for acne.
Iodine: The link between iodine and acne is even more theoretical than with dairy. However, some select scientists put out the possibility that if iodine does in fact aggravate acne, since milk contains iodine, milk could lead to more acne.
The bottom line:
What stands out strongly now that I have read all of the evidence is that the design limitations in dairy and acne studies thus far leave us without any concrete answers. After performing a thorough review of existing evidence, authors in the Journal of Clinics in Dermatology agree: “Our conclusion, on the basis of the existing evidence, is that the association between dietary dairy intake and the pathogenesis of acne is slim.”
My common sense takeaway:
Northern Europeans were the first to domesticate animals and drink milk past childhood. In fact, the last genetic adaptation we see in humans is the gene which allows people of Northern European ancestry to digest lactose. If you can drink milk and eat dairy products without stomach aches, excess gas, or discomfort, perhaps ingesting dairy is part of a healthy lifestyle for you. However, for the rest of us, me included, if you do not have the gene, and dairy gives you issues, that’s a pretty clear sign that your body isn’t crazy about dairy. It might be a good idea to steer clear of it for overall health. As far as acne in particular is concerned, we just don’t know yet. I personally love pizza more than breathing and I’m not going to give up dairy completely until I see more concrete evidence linking it directly with acne or other serious negative health consequences.