Travelling and dragging your suitcase along with you can not only make it extremely dirty, but it can damage it, too. If your suitcase have accompanied you on your trips for a long time, it's zipper is stuck or the insides are torn, it's maybe time to change it with a new one. But if the damage is not that big, you may consider cleaning it. Different cleaning solutions can damage the fabric that your suitcase is made of. So you better check your user's manual before you start cleaning your suitcase.
