There are numerous synonyms for the phrase "quality loss" that can be used depending on the context in which it is used. Some of the synonyms that can be used in place of "quality loss" include degradation, deterioration, decline, impairment, and decay. Another commonly used synonym is "downgrade," which implies a reduction in the quality of a product or service. "Diminishment" and "weakening" are also effective synonyms of quality loss that can be used to describe a reduction in the overall value or effectiveness of a product or service. Whatever synonym is chosen, it should effectively convey the idea of a decrease in quality, performance, or capability.