Joyful: The Surprising Power of Ordinary Things to Create Extraordinary Happiness

by Ingrid Fetell Lee

In Japan, an activity called shinrin-yoku—literally, “forest bathing”—has been promoted as a public-health initiative by the forestry ministry since 1982. The practice, which involves simply relaxing in the presence of trees (no actual “bathing” required), has been shown in several studies to increase the activity of natural killer (NK) cells, a type of white blood cell critical to immune system functioning, particularly in the body’s defense against cancerous and virally infected cells. The researchers attribute part of the forest’s immune-boosting influence to a series of chemicals known as phytoncides, which are secreted by plants to protect themselves from pests and diseases and are present in some essential oils. In a related test, researchers used a humidifier to infuse hotel rooms with essential oils from the hinoki cypress, a tree common in Japan’s forests. Just the presence of phytoncides in the air was enough to decrease stress hormones and raise NK cell activity.