If you have ever been told by a doctor that what you eat has no impact on your skin, you were not alone and you were not being misled out of carelessness.

You were on the receiving end of a consensus that had been passed down through dermatology textbooks for five decades.

A consensus built almost entirely on a single study from 1969 that should never have shaped anything.

The Fulton Study: How One Paper Became Medical Gospel

In 1969, Dr. James Fulton published what would become the most cited study in the dermatology–diet conversation.

The premise was simple:

• 65 subjects were given either a high-chocolate bar or a control bar
• The study ran for four weeks
• Acne severity was graded at the end

The conclusion:

There was no significant difference between the two groups.

This finding was taken as definitive proof that diet plays no role in acne.

But there’s a detail that should have raised immediate concern:

The study was funded by the Chocolate Manufacturers Association of the USA.

Instead of scrutiny, it became doctrine.

Through the 1970s, 80s, and 90s, dermatology textbooks didn’t cite a body of evidence - they cited this one paper.

A later review found that major dermatology textbooks relied on just two weak references to dismiss diet entirely.

Three Reasons the Study Was Fundamentally Broken

1. The “Control” Was Not Neutral

The control bar contained 28% hydrogenated vegetable oil - essentially trans fat.

Today, we know:

• Trans fats drive systemic inflammation
• Inflammation is a key contributor to acne

So both groups were consuming pro-inflammatory ingredients.

The result?
No difference between groups - not because chocolate is harmless, but because the control was equally problematic.

2. The Methodology Was Weak

• Subjects were prisoners
• No baseline acne data was recorded
• No quantitative measurement of outcomes
• Sugar and fat content between bars were nearly identical

There was no way to isolate chocolate as a variable.

Which defeats the entire purpose of a controlled study.

3. It Was Never Properly Challenged

The biggest issue wasn’t just the flawed design.

It was that no one questioned it for decades.

The study became the foundation for a sweeping claim:

Diet and acne are unrelated.

And that claim hardened into medical fact without sufficient evidence.

What the Science Has Caught Up To

It wasn’t until around 2011 that this consensus began to unravel.

Since then, research has consistently pointed in a different direction.

High Glycaemic Diets and Acne

A 2012 systematic review in the Journal of the Academy of Nutrition and Dietetics found consistent links between:

• High glycaemic load diets
• Increased acne severity

Proposed mechanism:

• Refined carbs → spike insulin & IGF-1
• IGF-1 → stimulates sebaceous glands
• Increased sebum → higher acne risk

Dairy and Acne

Multiple studies, including those published in the Journal of the American Academy of Dermatology, show:

• Higher milk consumption
• Increased acne prevalence

Particularly with skim milk.

Why?

• Dairy contains hormonal components
• These interact with the IGF-1 pathway, amplifying acne triggers

The Gut-Skin Axis

Once dismissed as fringe, the gut-skin axis is now a serious area of research.

Diet influences:

• Gut microbiome diversity
• Intestinal permeability
• Systemic inflammation

And that inflammation doesn’t stay internal, it often shows up on the skin.

A 2024 study represents one of the most rigorous attempts yet to isolate dietary effects on acne using proper controls.

The Takeaway for Your Skin

None of this means chocolate causes acne in everyone.

Skin is individual.

Triggers vary.

But what is clear is this:

The blanket dismissal of diet for 40+ years was never based on strong science.

It was based on one flawed, industry-funded study that went unchallenged for far too long.

Diet is not the sole cause of acne.

But it is also not irrelevant.

Modern research shows clear biological pathways linking:

• Blood sugar
• Hormones
• Inflammation
• Gut health

To acne development.

Understanding what you eat and how your skin responds is not pseudoscience.

It is where the science is now pointing.

FAQ 

Does diet actually affect acne? Yes. Modern research shows links between high glycaemic diets, dairy, and acne through hormonal and inflammatory pathways.

Did chocolate really cause acne? There is no strong evidence that chocolate alone causes acne, but the 1969 study that dismissed diet entirely was flawed.

Why was diet dismissed in acne for so long? Because of a widely cited 1969 study with major design flaws that shaped dermatology teaching for decades.

Does sugar cause acne? High sugar intake can increase insulin and IGF-1 levels, which may trigger excess oil production and worsen acne.

Is dairy linked to acne? Some studies show an association between milk consumption and acne, possibly due to hormonal effects.

What is the gut-skin axis? It refers to the connection between gut health and skin inflammation, where diet influences acne through the microbiome.