You have probably heard that drinking milk and eating chocolate causes acne or, at the very least, that they make it worse. Diet is often blamed for a teenager’s pimply skin, but is there good evidence behind this accusation?
Acne (or more precisely acne vulgaris in medical circles) is a chronic inflammatory disease that affects what we call the pilosebaceous unit. Put simply, the pilosebaceous unit is made up of a hair shaft, the hair follicle, the muscle that can pull that hair up to give you goosebumps, and a sebaceous gland which produces sebum. It’s a hair growing out of the skin and its associated oil gland.
Given that acne is not a new disease, you may be surprised to learn that we still don’t know the precise sequence of events that transform a healthy skin into one covered in zits. There are, however,  that play a role in acne.
The first is excess sebum. The oily substance secreted by our sebaceous glands is often overproduced in adolescence because of changes in our hormones. However, not everyone with acne has an excess of sebum. The composition of our sebum also changes in early adolescence, which has been flagged as a major reason for the onset of acne.
The second factor is inflammation: molecules that trigger an inflammatory response start to be released into the skin.
A third element has to do with the structure of the skin itself. Living skin cells are transformed into dead cells filled with the protein keratin, and this process is known as keratinisation. In acne, this process is altered. Dead cells filled with keratin accumulate inside the hair follicle, which clogs up the sebaceous gland or blocks the follicle itself.
The final ingredient in this acne recipe is a bacterium known as Cutibacterium acnes (formerly called Propionibacterium acnes).ĚýC. acnes is a common resident on healthy skin, but some strains are more prone to creating inflammation. As our skin produces more sebum, C. acnes feeds on the triglycerides present in it, cutting them up into  and contributing to acne lesions.
Because we have a high density of pilosebaceous units on our face, neck, shoulders, upper chest and back, acne is more commonly found there.
The idea that diet may influence acne is often backed up by a startling observation: communities which live under paleolithic conditions—namely the Aché Hunter-Gatherers of Paraguay and the Kitavan Islanders who live to the northeast of Australia—, according to visits made by Dr. Staffan Lindeberg in the 1990s. (Before arguing, though, that a paleo diet low in carbohydrates might prevent acne, it’s important to point out that 70% of the Kitavans’ daily energy came from carbs.)
Lindeberg and his team published a  in 2002, provocatively titled “Acne Vulgaris: A Disease of Western Civilization.”
Is the Western diet to blame for acne?
Milking the literature for answers
Despite decades of research to clarify the issue, experts can only say that the association between acne and the typical Western diet is inconsistent, debated, and evolving.
This is because forcing teenagers to eat a certain way is very, very difficult and is rarely done. A systematic review and meta-analysis—the highest form of scientific evidence, though not without flaws—published in  showed that consumption of any dairy (meaning milk, yogurt, and cheese) was associated with an increased risk for acne, and this conclusion came from looking at 14 separate studies. The problem? The studies themselves were deeply flawed. In nearly half of them, acne was self-reported instead of being assessed by a doctor. None of the studies were randomized trials; instead, the authors of the review specifically only looked at observational studies, where participants do what they naturally do, and causation is much harder to prove in these cases. Plus, there was clear evidence of publication bias, meaning that studies that did not show a link between dairy and acne were apparently not published, thus skewing the body of evidence toward blaming dairy for acne.
Another review article from  states that the influence of milk on this skin condition is unclear, but that hasn’t stopped scientists from  as to how dairy products łľľ±˛µłółŮĚýcontribute to acne. Amino acids found in milk proteins promote the secretion of insulin in the body, and this can increase the synthesis of a protein called insulin-like growth factor 1, which has been suggested as an important mediator of acne. Another  involves the growth factors present in cow’s milk, which could stimulate the production of sebum and accelerate the keratinisation alterations that are a hallmark of acne. Whether any of this happens at a significant level remains to be demonstrated beyond the shadow of a doubt.
Chocolate has also been implicated in acne, but . Some studies have used milk chocolate, which introduces another variable in the mix: if acne increases, is it because of the cacao or the milk, or even the sugar?
Yet other researchers have focused on the  of the food we eat. Foods with a high glycemic index raise blood sugar high and fast. They include many breakfast cereals and rices, as well as watermelon. Foods with a low glycemic index—including apples, oranges, peas and, ironically, cow’s milk and yogurt—have a much smaller impact on blood sugar levels and their consumption is suspected of leading to fewer pimples. But  and the jury is still out.
While the role of diet in causing or aggravating acne remains to be fully elucidated, dermatologists do know a few things. Acne is not due to dirty skin. Acne has a clear hereditary component: if a close family member of yours has or had acne, your risk of developing it are  than it would otherwise be. Excessive washing or scrubbing of the skin can make the acne worse, because it strips the skin of its oil and stimulates more production of sebum. And, importantly, .
The role of diet here may still be unclear, but one thing is certain: aiming to eat healthier in general has a wide range of benefits, regardless of whether or not it helps with acne.Â
Take-home message:
- Acne happens because of four main factors: an increase in the production of sebum, the release of inflammatory molecules, the clogging up of pores due to dead skin cells filled with keratin, and changes to a skin bacterium called C. acnes
- Acne is not due to dirty skin, and excessive scrubbing of the skin can actually make acne worse
- It is still unclear if diet causes acne or makes it worse, with various people pointing the finger at dairy products, chocolate and high-glycemic index foods, although the body of evidence is so far inconclusive
