Oh, are you eating the banana peel too, po? Because if not, then the outside is just for holding. Same with avocado. Unless your planning to make some fancy avocado skin crisps, which I've seen on the internet. For potatoes, if your peeling them, then your washing away the dirt with the skin, di ba? But good practice to rinse it first so your hands don't transfer the dirt to the flesh. And for cooking really thoroughly? Well, if you cook it to a crisp, your probably burning away all the germs. But then, is it still food or just charcoal? Hehe.