The human species have existed for 6-7 million years. Because over 99.99% of our evolutionary history has been spent in natural environments, it is considered that we are adaptive to nature1). However, we now live in a society that is characterized by urbanization and artificiality, despite our physiological functions still being adapted to nature.   We conducted experiments involving 420 subjects at 35 different forests throughout Japan2). Participants in natural surroundings showed the following physiological decreases compared with those in an urban control group: 12.4% decrease in cortisol level, 7.0% decrease in sympathetic nervous activity, 1.4% decrease in systolic blood pressure, and 5.8% decrease in heart rate. This suggests that stressful states can be relieved by forest therapy. In addition, parasympathetic nervous activity was enhanced by 55.0%, indicating a relaxed state. The results of similar experiments that involved walking in forests were equivalent. Li et al. demonstrated that immune function was enhanced by forest therapy in middle-aged employees who volunteered to participate in these experiments. Natural killer cell activity, an indicator of immune function, was enhanced by 56% on the second day and returned to normal levels. A significant increase of 23% was maintained for 1 month even after returning to urban life, clearly illustrating the preventive benefits of forest therapy3).   In conclusion, forest therapy had preventive benefits and facilitated physiological relaxation and immune recovery4) (Figure 1).