Peter are you always visiting clinics/docs? I often get this on my back, the keyword is the bump full of pus, and doesn't go away   Cystic acne happens when this infection goes deep into your skin, creating a red, tender bump that's full of pus. It may hurt or itch. If a cyst bursts, the infection can spread, causing more breakouts. I don't think TS has that, his is a v small one