Banana peels can be used to whiten teeth, although some claim that it is a somewhat ineffective way of doing so.
Those who wish to whiten their teeth using banana peels will need to rub them in a circular motion just a couple times each week. It will be important to use a ripe banana so you will be able to get the most amount of potassium. Make sure to peel from the bottom of the banana; this will prevent any problems with loose threads.
Just like with any other whitening method, it will be important to stick with it until you start seeing results.