Mood rings are jewelry items that change color based on the wearer's body temperature, which is believed to reflect their emotional state. The rings contain a thermochromic element, usually a liquid crystal, that reacts to temperature changes. Different colors are associated with various moods, such as blue for calmness and red for excitement. Originally popular in the 1970s, mood rings have become a nostalgic accessory and are often given as gifts. While they are not scientifically proven to accurately represent emotions, they remain a fun and intriguing way for people to express their feelings and connect with others through shared experiences.