This study uses an experience, traditionally known as "forest air bathing" (shinrin-yoku in Japanese), which has been part of Asian cultures for centuries and has been studied empirically for more than a decade. People go to the forest to be enveloped by pleasant sights, sounds and smells. Of particular medical interest in forest therapy are aromatherapy compounds known as "phytoncides", a class of natural terpenes produced by many forest trees that have NK immunostimulating properties both in vitro and in vivo. Many shinrinyoku studies have shown NK modulation effects in healthy participants; however, this study is one of the first to measure levels of oncotoxic cytokines in a clinically relevant population. Although the study design precludes directly attributing the causality of the increase in biomarkers to forest exposure, previous studies providing evidence of similar effects on NK cells suggest that such a cause-and-effect relationship is present.  

Of course, the potential immunomodulation of phytoncide exposure is not the only benefit of participating in forest therapy. Reduction in allostatic load (eg, blood pressure, cortisol, HRV, IL-6, TNF-a) resulting in decreased inflammation and autonomic nervous system dysfunction is a well-reported set of benefits. Another is the improvement of positive and negative mood and associated clinical ailments. Other mental benefits of "contact with nature" include improved cognition, memory and attention, as well as greater feelings of prosociality, a sense of purpose, spiritual connection and quality of life. All of these impacts of forest therapy make it a potentially valuable holistic approach to health promotion for all and everyone, including cancer patients.