But for many years inconclusive studies meant that any link between food and acne was at best unproven, and at worse a myth. Then in 2002 came the intriguing finding that no one in non-westernised populations in New Guinea and Paraguay had acne. Suddenly diet was back on the agenda. Of course there is the possibility it is genetics that is protecting these populations from acne, but if diet does make a difference, then we need to know which kinds of foods in industrialised countries are having the biggest impact on acne. Is it the amount of fat consumed that matters, or sugar, or as some have suggested, the speed at which the sugar breaks down (high versus low glycaemic diets)?
Again, reviews can’t help us – they conclude that there’s not enough evidence to know what is happening. A review in 2009 looked at 21 observational studies and six clinical trials and concluded that dairy products made a difference, but not chocolate in particular. However, before you think about cutting out dairy products, bear in mind that this review included some trials with very few participants and no control groups. As the authors of a review published last year point out, some of these studies simply asked people what they believe exacerbates their acne, rather than what is clinically proven to do so. This is not a reliable method because we all have a tendency to look for links if we have heard they might be true.
The fact is that regardless of what people eat, their acne usually gets better when they leave their teens. So if we are ever to discover the answer, what we need are well-designed prospective studies. And that means tracking people across many months or even years while assessing their chocolate consumption and the severity of their acne. Ideally they need to be randomised either to eat lots of chocolate or none at all. The trouble is that when volunteers get no say as to which group they end up in, this might not be a study that people rush to join.
If you would like to comment on this article or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.
You can hear more Medical Myths on Health Check on the BBC World Service.
Disclaimer
All content within this column is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. The BBC is not responsible or liable for any diagnosis made by a user based on the content of this site. The BBC is not liable for the contents of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites. Always consult your own GP if you're in any way concerned about your health.
