The idea behind a mood ring is simple: Wear it on your finger and it will reflect the state of your emotions. The ring's stone should be dark blue if you're happy, and it will turn black if you are anxious or stressed. While mood rings cannot reflect your mood with any real scientific accuracy, they actually are indicators of your body's involuntary physical reaction to your emotional state.

If you take a moment to think about the moods represented by the colors, you'll see a definite correlation between your body's surface temperature and the color of the liquid crystals contained within the mood ring. When you are in a passionate mood, your skin is usually flushed. This is a physical reaction to an emotion, causing the capillaries to move closer to the surface of the skin and release heat and change the color of the ring. Conversely, when you are nervous or stressed, your skin may feel clammy. This physical reaction to your emotional state causes the capillaries to move deeper into your skin, causing the surface temperature to drop and the color change of the mood ring will reflect that.