Chocolate. No good evidence that chocolate specifically causes acne. Studies have been small and inconsistent, and confounded by the sugar and dairy that usually accompany it.
Greasy food. Eating fat does not put oil in your skin. The sebum causing acne is produced by sebaceous glands under hormonal control, not delivered by chips.
Poor hygiene. Acne is not caused by dirt, and over-washing makes it worse by damaging the skin barrier.
These persist because they place the blame on the person, which is both wrong and unhelpful.
Where There Is Some Evidence
High-glycaemic-index diets
The strongest signal. Diets high in rapidly absorbed carbohydrates — white bread, sugary drinks, most confectionery — raise insulin and IGF-1, which influence sebum production and follicular cell turnover. Several studies of low-glycaemic-load diets have reported improvements in acne.
The effect is modest and not universal, but the mechanism is plausible and the change is generally good for you regardless.
Dairy, particularly skimmed milk
Observational studies have found associations between milk intake — skimmed milk more than whole — and acne. The proposed mechanism again involves IGF-1 and hormones present in milk.
The evidence is associative rather than causal, and the effect sizes are not dramatic. It does not justify cutting out dairy entirely, particularly in teenagers who need calcium for bone development.
Whey protein supplements
Case reports and small studies associate whey protein with acne, especially in young men who start it and flare. If your acne worsened after starting a supplement, the timing is worth acting on — this is one of the more actionable dietary observations.
What Is Not Supported
- Food intolerance testing for acne — no established role
- Elimination diets without a specific reason, which risk nutritional deficiency for uncertain benefit
- Detox regimes and juice cleanses
- Most acne supplements, where the evidence is weak and the marketing is not
The PCOS Exception
In women with polycystic ovary syndrome, insulin resistance is part of the underlying condition, and dietary and metabolic management is genuinely part of treatment. NICE's acne guideline includes management options for people with acne and PCOS specifically. If you have irregular periods, unwanted hair growth and persistent acne, that combination is worth investigating rather than treating as three separate problems.
The Proportion Worth Keeping
Dietary change is at most an adjunct. It is not a substitute for benzoyl peroxide, a topical retinoid, antibiotics where indicated, or isotretinoin for severe acne. Someone with scarring cystic acne needs treatment now, not a reduction in milk.
What dietary advice should never do is imply the acne is the patient's fault. It is a condition with a strong genetic and hormonal basis, and people with it have usually already tried everything they have been told to try.
If You Want to Experiment
Change one thing, keep everything else constant, and give it at least eight to twelve weeks — acne responds slowly to anything. Photograph your skin in consistent lighting at the start. And keep taking your treatment while you do it, so that if something improves you know it was not simply the treatment finally working.