"The purpose of forest therapy is to provide preventive medical effects by relieving stress and recovering the immune system [diminished]by stress," Yoshifumi Miyazaki of Chiba University explained. As Japan's leading scholar on forest medicine, he's carried out studies across the country. The results show forest bathing can significantly lower levels of cortisol, a stress hormone, along with blood pressure and heart rate. Other research points out that walking in the woods can boost the body's immune system by increasing anti-cancer proteins and enhancing the so-called natural killer activity of certain cells. In this case, it's believed humans benefit from breathing in phytoncides, the chemicals plants emit to protect themselves from rotting and insects.