Usually red marks cannot be completely avoided. However, if the marks are painful or become open sores, your mask is not a proper fit or it is not adjusted correctly. When wearing a nasal mask it should fit directly on the bridge of your nose and the bottom sitting in between your top lip and bottom of your nose. The mask should not sit directly under your nostrils (mask is too small) nor should it sit on the top of your lips (mask is too big). A full face mask should sit directly at the bridge of your nose and in between your bottom lip and the bottom of your chin. If the mask sits on or under your chin it is too big. If it sits on your bottom lip it is to small.