It's been a few years since I've posted on earthclinic and this isn't one I have tried personally, rather found it online while conducting some research for a family member with this issue. There is a ton of info online stating that this method works even for moderate to severe acne because of the potassium and antioxidants contained in the peel. Because this is such a cheap and accessible item, and because I found glowing articles even on mainstream 'beauty' sites and such, I had to add it here. I recall info about peels for warts but did not know it helped acne.
I would suggest doing some reading online but essentially the method involves taking a fresh banana peel (yellow with brown spots works best, do not use green) and rubbing on the face for up to 10 minutes. The peel will get discoloured from rubbing on the face, and when that happens, new peel area should be used. Let this sit on the skin for some time. Some articles I read advised doing this up to 3 times per day.
I have pointed my family member in this direction and will report on the results. Surely if acne is severe many other measures should be taken, but this seems like a cheap and easy ritual to add in. It's all about good habits and remedies adding up. I wish I had known about it years ago!