If you've moved your bathroom throw rug and found a yellow stain on the vinyl or wood flooring, you've also discovered firsthand that nothing will remedy the situation. That is the bad news. The good news is that once you know what causes the yellowing, you will never have to have it happen in your home again.
Check the label on the bath rug. If rubber or latex -- or isoprene or elastomers -- is a component ingredient, don’t use it. This is the rubbery backing on area rugs, typically white, that prevents the rug from slipping on the floor. Unfortunately, rubber, latex, isoprene or the elastomers and the vinyl flooring don’t react well together -- the chemical reaction can cause the vinyl to yellow. There is no fix for this; the coloring is permanent, so prevention is the best defense.
Move the rug off the floor when it's not in use. Leave these rugs on the floor as little as possible. Make sure the floor is dry when the rug is in place. Don't use the rug at all if the latex backing is crumbling or disintegrating.
Keep sunlight off the floor. Sunlight may cause the floor around the rug to change color, creating a shadow where the rug normally lies. Blackout blinds and drapes will help prevent the problem, but even indirect light can affect wood or engineered wood floors.
Remove all paste wax from the floor. Sunlight can cause paste wax to yellow. Direct light will affect the floor at different rates, depending on the angle of the sun and the frequency of rug use. Because the area outside the rug perimeter may color more quickly and more substantially than the space under the rug, the rug-covered area may appear more yellow. Use a clear liquid wax that is designated as non-yellowing.
Apply a new back to the rug. Cut a piece of mesh gripper fabric in the same shape and size as the rug, and apply it to the back of the rug. Either hand sew or use two-sided carpet tape. Make sure the mesh gripper fabric does not contain latex or rubber.
Attach a ready-made carpet pad to the underside of the rug, or cut one to fit. Hand-sew it in place, or use two-sided carpet tape.