Up to 80% of us will get acne to some degree. A study of final-year medical students at Melbourne University found many believed that fatty and sugary foods were second only to stress in causing spots. As the researchers leading the study pointed out, these beliefs were not based on evidence.

Those silly medical students. Why didn’t they consult the British Association of Dermatologists’s patient leaflet that says there is “little evidence that any foods cause acne, such as chocolate and fast food”? Yet a new book by two dermatologists – Perfectly Clear: The Perfect Guide to Clear Skin – says that restricting refined processed carbohydrates (such as sugar, white flour and white pasta) can reduce acne. Research from the British Medical Journal also shows that a diet high in dairy, particularly skimmed milk, can increase severity of acne. Greasy foods in general? Not so much.

Acne is caused by oil-producing glands in the skin getting blocked, leading to blackheads, redness and spots with pus where bacteria infiltrate the area. Production of oil (sebum) is increased by sex hormones, hence the appearance of acne at adolescence. Acne is definitely not caused by dirty skin. However, diet may have a role, albeit a small one. So should you modify your diet if you get spots?

The solution

Milk may increase acne because cow feed includes sex hormones – these then stimulate sebum production and foster spot formation.

Since foods with a high glycemic index (HGI) – those that make blood glucose rise quickly – increase the release of sex hormones, it’s not clear why skimmed milk is a villain. Some researchers think that drinking it makes people eat more HGI foods than if they drank a fattier variety.

The evidence overall is still underwhelming; it is often gathered from small groups of people and is observational in nature, so cannot attribute cause. It also often relies on people remembering what they ate many years ago.

But non-western diets are said to keep populations free of acne – a study of Inuit in 1971 showed that only when they gave up their nomadic life and started eating refined sugar in settlements did they get spotty. Genetics, however, are also likely to play a role. The American Academy of Dermatologists now says “emerging data suggests that HGI diets may be associated with acne”. But it also says that the evidence is not strong enough to advise people to change their diets. Of course, you shouldn’t eat refined, processed carbohydrates anyway – because, regardless of spots, they make you fat and can give you diabetes. The students were right about stress, though – a study showed that exams caused flareups of acne.