Yellowed plastic is not that difficult to clean, but when your yellowed plastic is in the form of a plastic tub surround, tackling it effectively can be a bit of a challenge. Fortunately, you can whiten, brighten and clean a yellowed plastic tub surround effectively with a just a little patience and ingenuity---and a few items that are likely sitting in your medicine cabinet right now.
Clean the tub thoroughly. Use a mixture of 2 cups warm water and 5 drops of dish detergent in the spray bottle to wash away all dirt and grime. This will make the rest of the treatment easier to accomplish since you will only be dealing with the yellowing problems.
Saturate the rags with hydrogen peroxide. As you soak a rag, place it on the tub surround. Continue until you have covered the entire surround with hydrogen-peroxide soaked rags. Let the rags sit for 30 minutes.
Remove the rags. Apply another coat of hydrogen peroxide using the spray bottle. The surround should be entirely coated with hydrogen peroxide.
Expose the tub surround to the ultraviolet light. You can shut the door and leave the UV light on for 24 hours. It will interact with the hydrogen peroxide to whiten the yellowed plastic. Once every 45 to 90 minutes, reapply the hydrogen peroxide, turning off the UV light before entering the bath area, then turning the UV light back on when you leave.
Wipe down the tub with the dish-soap solution again. This will remove any hydrogen peroxide residue and leave your tub sparkling clean and ready for use.
Remove hard water stains, which may be yellow or brown and raised off the surface of the tub, with baking soda and the plastic scrubber in addition to hydrogen peroxide.
Always protect your eyes from UV light.