Sometimes, light colored rugs can appear to yellow over time.  This can happen to carpets, rugs, drapes and other textiles.  This yellowing usually happens gradually, and often is not particularly noticeable until after a rug is cleaned. This can lead a customer to naturally assume that the cleaning was the cause.  There are a number of potential causes of yellowing in rugs, and usually the cleaning process is not the culprit, but it can expose some pre-existing conditions in the rug, leading to the visible discoloration. Early forms of stain resistant finishes, especially those based on silicone, and early types of nylon are common causes of yellowing, especially with exposure to UV light.  

The use of fluorescent brightening agents can lead to yellowing.  These agents are found in many detergents and spot cleaners, sometimes used by professionals but more commonly sold to homeowners, and although they are not recommended for use on area rugs, many people still use them because their packaging does not make this clear. The latex used in the backing of tufted rugs can cause the face to yellow through a condition known as off-gassing.  

Some fibers are prone to photo-oxidation where combinations of exposure to sunlight and off-gassing from home furnishings cause rug fibers the fibers yellow over time. Often, light colors are achieved through the use of several different  dyes. 

Over time these dyes can fade at different rates, altering the color’s appearance.  Finally, sometimes a rug has already yellowed but it has been covered up by soil and only after the soil has been removed does the discoloration reveal itself. Your cleaner has multiple ways to improve the appearance of a rug that has yellowed.  

There are specialized color strippers and bleaches that can be effective, and sometimes altering the rug’s pH level can improve its look.   Sometimes through these techniques yellowing can be removed completely, but often the most that can be achieved is some improvement but not complete removal.  As noted above there are several causes of yellowing, most of which are pre-existing conditions, so it will be up to your cleaner to determine the best course of action.