In short

Diet probably plays a supporting role in acne, but it's not the main driver. The evidence is strongest for high-glycaemic foods (sugary and highly processed carbohydrates) and, to a lesser extent, dairy, affecting acne.

A low-glycaemic diet has been shown in randomised controlled trials to reduce acne lesion counts. Chocolate and "junk food" on their own don't have strong evidence behind them. 

The hormonal changes during the stages of puberty are the primary cause and diet is a modifier, not a root cause.

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Does diet cause acne?

It's more complicated than a simple yes or no. Acne is fundamentally hormonal, driven by testosterone acting on the skin's oil glands during puberty. 

Diet doesn't cause that process, but it may influence how severe the acne is.

While there's no definitive evidence that diet causes acne, observational evidence suggests that foods that raise blood sugar quickly may be linked to the development or worsening of spots.

What does the research say about sugary foods and acne?

A randomised controlled trial published in the American Journal of Clinical Nutrition found that young men aged 15 to 25 who followed a low-glycaemic-load diet for 12 weeks had significantly fewer acne lesions than those who ate a high-glycaemic diet.

The theory is that high-glycaemic foods spike insulin levels. 

Insulin-like growth factor (IGF-1) is then released, which stimulates the oil glands in a similar way to testosterone, compounding the hormonal effect that's already driving the acne.

High-glycaemic foods to be aware of include:

• White bread, white rice and refined pasta
• Sugary drinks and fruit juices
• Biscuits, cakes, sweets and highly processed snacks

Switching to whole grain versions and including more vegetables and protein doesn't have to be a dramatic overhaul. Small shifts can make a difference.

What about dairy?

Dairy is the second area where evidence has accumulated. Some studies have found links between milk consumption and acne, possibly because milk contains hormones and proteins that stimulate oil production. 

However, the evidence here is less consistent than for glycaemic load, and the NHS doesn't currently recommend avoiding dairy specifically.

If your daughter suspects dairy is a trigger for her personally, she could try reducing it for six to eight weeks and see if there's a difference, but this isn't a recommendation for everyone.

Does chocolate actually cause spots?

The link between chocolate and acne is one of the most persistent myths. The NHS states there is no evidence that chocolate or junk food causes excess oil or spots. 

However, highly processed chocolate that's high in sugar and fat may indirectly affect acne through the glycaemic route. 

Plain dark chocolate has a much lower glycaemic index than milk chocolate.

The overall quality of the diet matters more than any single food. There's no need to ban chocolate entirely.

What foods might actually help?

A diet that can help your daughter manage acne includes:

• Whole grains, legumes and vegetables (low glycaemic index)
• Oily fish like salmon, mackerel and sardines (omega-3 fatty acids have anti-inflammatory properties)
• Plenty of water
• A variety of colourful vegetables and fruits

FAQ

Should my daughter cut out dairy completely to help her acne?

There's no need to cut it out entirely based on current evidence. 

If she wants to test whether dairy is a personal trigger, she could reduce it significantly for a couple of months and track whether her skin responds. 

Any change should be balanced. If she reduces dairy, she needs other sources of calcium. Speak to a doctor if she's thinking about significant dietary changes.

Can vitamins or supplements help with acne?

Some studies suggest zinc supplements may help with mild to moderate acne. Omega-3 supplements (or increased oily fish intake) may also reduce inflammation. 

However, daily vitamins are not a substitute for proven acne treatments. If her acne is significant, treating it medically is the priority, dietary tweaks are supplementary.

Is it worth keeping a food diary to spot triggers?

Yes, this can be a useful exercise, particularly if she suspects certain foods make things worse. 

A two to three week diary tracking what she eats and how her skin looks can reveal patterns. Bear in mind that acne also fluctuates with the menstrual cycle, so it's worth noting where she is in her cycle too.

For context on everything else that might be driving her skin changes, luna's article on teen hormones affecting periods, skin and mood fills in the broader picture. 

And for a full overview of nutrition for teens, luna's healthy eating for teenage girls guide is a good companion read.

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