h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"Of course, acne-avoidance is governed largely by diet"

Actually, most experts now agree that diet doesn't play a significant role in the prevention or cause of acne. A study published in the Journal of the American Medical Association: “Diet plays no role in acne treatment in most patients…even large amounts of certain foods have not clinically exacerbated acne.”

The best prevention for acne is to control the amount of oil and bacteria in our skin with hygiene and some of the methods you've already listed.

Also, to control oil, I use a small amount of Milk of Magnesia on my face every morning when I get out of the shower. It absorbs excess oil throughout the day.

Certain food allergies, notably lactose intolerance, are known to cause acne/blemishes. A friend of mine swears by chamomile oil for them.

It might be correct to say, 'in certain unusual cases, diet can affect acne'. In any case, as it is written now, it is definitely wrong.

Lactose intolerance runs in my family, and no one has any difficulty determining whether a bump is a lactose reaction vs a pimple: they're itchy, shape and grow differently, and are typically associated with other (non skin) problems.