A mood ring is a type of jewelry that changes color based on the wearer's body temperature, which is believed to reflect their emotional state. The ring typically contains a thermochromic element, often 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 seen a resurgence in interest due to their unique design and the fun of interpreting their color changes. They are often worn as fashion accessories and are sometimes given as gifts, appealing to both children and adults alike.