 Acne affects nearly 1 in 10 people in the world, making it perhaps the eighth most prevalent disease worldwide. What's the role of nutrition? Well, go back a century, and dermatology textbooks were recommending various dietary restrictions. For example, recommending those with acne-avoid foods like pork, sausage, cheese, pickles, pastries, sweets, cocoa, and chocolate. Yeah, but old-timey medicine was full of crackpot theories. Dr. Kellogg, for example, blamed acne on masturbation. Nothing a few corn flakes couldn't fix, though. Population studies have found associations between acne and the consumption of foods like dairy, sweets, and chocolate, but you don't know if it's caused an effect until you put it to the test. There have been high-quantity reports like the Harvard Nurses study that looked at nearly 50,000 women and found a link between adolescent milk drinking and acne, particularly skim milk, something that's been found for teenage boys as well. They thought it might be the hormones in milk that were responsible, but it could also be the milk protein way of which they had extra to skim milk to make it less watery, which may play a role directly in acne formation or as hormonal carriers. That would explain cases like this, where whey protein powders were implicated in precipitating acne flares in teens who had acne that just didn't seem to want to go away until they stopped the whey. It doesn't appear to just be a protein effect, since soy protein supplements, for example, did not seem to cause the same problem. But for dairy in terms of interventional studies, all we have are these kinds of case series. If you do a systematic review of acne and nutrition, you get results like this for dairy. Out of the 20 or so papers on acne and dairy out there, about three quarters suggest adverse effects, and the remainder report no effect, with no study suggesting a beneficial effect of dairy and acne. So you could look at this and conclude a dairy-free diet is worth a try, but this is based on low-grade evidence, level C and D evidence, where C is like the population studies, and D are like those series of case reports. What we want ideally are randomized interventional studies, level A and B evidence, which we don't have for dairy, but we do have for chocolate. When it comes to acne, no food is more universally condemned than chocolate. So if you're the Chocolate Manufacturers Association, how are you going to design a study to make your product not look so bad? You can always use the old drug company trick of pitting your product against something even worse, and so they fit people chocolate bars versus fake chocolate bars, made out of a partially hydrogenated vegetable oil, trans fats. So make it have more sugar, throw in some milk protein, and make it 28% pure trans-fat-laden Crisco like vegetable shortening. And surprise, surprise, there were just as many pimples on the fake chocolate bars, allowing them to conclude that eating high amounts of chocolate is A-OK when it comes to acne. And the medical community fell for it. Have we been guilty of taking candy away from babies? Too many patients harbor the delusion that their health can somehow be mysteriously harmed by something in their diet. That original study, finding that chocolate consumption supposedly does not exacerbate acne, has continued to remain virtually unchallenged for decades and continues to be cited even in recent reviews. For example, this Pediatrics Journal years ago was demonstrated that chocolate consumption has no effect on acne. This serves as a cautionary example of how research-based evidence should be vigorously scrutinized prior to being incorporated into clinical practice. Just because something is published in the Journal of the American Medical Association doesn't necessarily mean it's a good study, especially when industry interests are involved. Maybe we should be telling acne patients to try cutting down on not only the sweets and the dairy, but also the trans-fats found in partially hydrogenated vegetable oils. But we can't be unequivocal in our advice to acne sufferers on foods to include or exclude until they're put to the test. It well-designed randomized controlled clinical trials, but there simply weren't any such trials on acne until now, which we'll cover next.