Astazio

By red marks I assume you mean scars from old acne. Shaving, especially with a blade that gets close to the skin, will take off a lot of the dead skin, including those around any scars. But I wouldn't shave over red marks just to try and get rid of them. If the marks are in your normal shaving area then they will probably go away a little sooner since you will be continually be shaving off dead skin cells. But even with shaving, red marks take a while to heal, depending on how many layers of skin have been scarred. I hope this helps.