Synonyms for the phrase "lose freshness" include phrases like "expire," "spoil," "go bad," "turn rancid," and "become stale." These phrases all describe a state in which food or other perishable items are no longer appealing or usable because they have lost their freshness. Other similar phrases include "degrade," "deteriorate," and "rot," which all imply a gradual breakdown or decay of freshness over time. Whether it's food in the refrigerator or an idea that has lost its relevance, these phrases all capture the sense of something that was once fresh and vibrant, but has now lost its appeal or usefulness.