I used to get bad acne as a teenager. I remember thinking it was some kind of cruel joke that I’d look in the mirror on Sunday night and see a fresh spot emerging, just as the others had cleared up, just as the school week was about to begin. Looking back, I think I understand what was happening. On Fridays I’d always eat a lot of sweets. They were banned in the household except for Fridays, and so we’d gorge on confectionary and fizzy drinks. Then, like clockwork, I’d break out in spots a couple of days later. So the culprit would seem to be refined sugar or some other common ingredient, taken in high concentration.

I can’t believe I didn’t figure it out at the time.