Vinyl flooring, a synthetic alternative to linoleum, is one of the easiest materials to clean, but yellowing can be problematic. It usually occurs underneath rubber-backed area rugs, and heat generated by the sun shining directly on the carpet is the culprit. The heat generates an irreversible chemical change in the polyvinyl chloride flooring material. If you act while the stain is still light, you may be able to remove some of it.
Let the Sun In
The simplest way to cure yellowing is to expose the stain to sunlight. Remove the carpet that has been covering the floor, and use mirrors, if necessary, to direct the sun's rays to the spot in question. This doesn't always work, but it's a painless solution, and doesn't involve the use of anything that can harm the floor. If you choose this option, give it at least two months to work before you try to physically clean off the yellowing.
Rub With a Mild Abrasive
A quicker method to remove the yellowing -- as long as it hasn't penetrated too deeply -- is to rub it out with a mild abrasive, such as baking soda. Sweep or vacuum all the dirt off the affected area, and wet it down with clear water. Sprinkle baking soda liberally over the area and let it stay there for 10 to 15 minutes, and then rub it away vigorously with a soft, nonabrasive cloth. You may have to repeat this treatment several times before you'll notice a difference.
Add an Acidic Cleaner
The cleaning action may be more effective if you use baking soda in conjunction with lemon juice; the citric acid acts as a gentle cleaner that won't affect the floor finish. Mix a solution of 2 parts lemon juice to 1 part baking soda in a bowl; stir it to make a paste, and apply the paste with a nonabrasive sponge. After rubbing the spot thoroughly, rinse with clear water and pat dry. As when you rub with pure baking soda, you may have to repeat this treatment several times.
Vinyl flooring manufacturers are aware of the problems associated with using rubber-backed carpeting and advise against it. Instead, they advise consumers to use vinyl-backed or woven rugs. You should look for the word "colorfast" on any carpet you're considering using, so you won't end up with dye or ink stains, which can be just as difficult to remove as yellowing. If you can't remove the yellowing that occurred under a rubber-backed carpet, and replacing the flooring isn't within your budget, the only alternative is to cover the spot with a larger carpet that won't cause further damage.