You may think removing dirt and oil is as simple as cleansing. But frequently, the things you use to wash your face may be guilty of depositing dirt or bacteria, themselves:
Bacteria thrive in damp environments. So if you’re going to use one on your face, use a fresh one each time.
Like washcloths, they can breed bacteria and transfer it to your face.
Dirt on your hands can wind up on whatever they touch. So be sure to wash them before washing your face.
Consider this: that bar has already been on your feet, underarms and... well, you get the idea.