Mood rings change color in response to temperature, which is supposed to reflect your mood. Eventually, a mood ring will turn black and stop responding.
It's reasonable to expect your mood ring to last a couple of years. Some mood rings last around five years. Few mood rings from the 1970s have survived with functioning stones to the present day.
Mood rings are notoriously susceptible to water damage. Most meet their end when water seeps into the stone of the ring and disrupts the liquid crystals, causing the "jewel" to become unresponsive or turn black.
Mood rings also may be damaged by exposure to high temperatures. And trying to resize a mood ring may damage it. Leaving the mood ring in a hot location, such as the dashboard of a car, also may irreparably damage the stone.
You can extend the life of your mood ring by removing it when your hands might get wet and by storing it at normal room temperature when you are not wearing it.