Don't do it for your acne, do it for your overall wellbeing
As part of a lifestyle overhaul for me, my regular aerobic exercise certainly doesn't hurt anything. I cleanse my face before and after I exercise and while I can't know that it's the exercise that is doing it, my acne has lessened a bit. It's said that exercise stimulates blood flow to the skin and helps unclog pores through sweating, both of which are beneficial. I think the greatest benefit for me is the stress management effect of exercising, which can certainly lead to fewer acne breakouts. Since beginning my treadmill routine I am naturally less inclined to eat things I shouldn't due to not wanting to negate my workout efforts. Net effect = healthier body/mind and slightly fewer pimples.