+1 for the anti-dandruff shampoo trick. I keep a bottle in the cabinet for when I work outside in the summer. It’s the only thing that prevents massive breakouts (all over my chest and shoulders) after I sweat a lot. Use it like a face/body wash, and let it sit for an extra minute or two (however long the bottle says) before you rinse. For particularly bad/stubborn spots, I use it like an overnight spot treatment. Dab it on directly and let it dry before bed, then rinse off in the morning.

It will only make a difference if the acne is actually fungal. But if it is, your friend will likely see a world of difference.