Cupping may leave temporary red marks on your back. The red marks are a result of the blood being pulled into that area. The darker the mark, the more stagnant fluids (toxins, blood and lymph) were dredged up during treatment. The marks last anywhere from a few hours to several days. The more often you receive cupping for the same issue, the lighter the marks will be. They will go away after a few days or a week, and for some it could take slightly longer.