One method of removing soap scum is to scrub the area with a damp cloth and baking soda. Hard-to-remove soap scum can be treated by spraying lemon juice on the affected area before scrubbing.
If the tub is made from a material besides granite, travertine or slate, difficult-to-remove soap scum can be scraped off with a tile scraper. Alternately, a paste of vinegar and baking soda can be applied to the affected area. After allowing the paste to remain for several minutes, scrub and rinse it.
Diluted vinegar also removes soap scum. A solution of half vinegar and half water can be sprayed directly on the affected surfaces. Allow it to remain for several minutes before cleaning with a sponge or cloth.
Diluted vinegar in a spray bottle can also be used to clean shower curtains. Spray the mixture directly onto the hanging shower curtain, and allow it to remain for several moments before rinsing. Plastic shower curtains with very hard-to-remove soap scum can also be washed in the washing machine on the gentle cycle. Add the recommended amount of laundry detergent to the machine, and wash the plastic shower curtain with several towels to help remove the soap scum.