But one of the biggest benefits may come from breathing in chemicals called phytoncides, emitted by trees and plants. Women who logged two to four hours in a forest on two consecutive days saw a nearly 40 percent surge in the activity of cancer-fighting white blood cells, according to one study. "Phytoncide exposure reduces stress hormones, indirectly increasing the immune system's ability to kill tumor cells," says Tokyo-based researcher Qing Li, MD, PhD, who has studied shinrin-yoku.

Read more: http://www.oprah.com/spirit/shinrin-yoku-health-benefits-of-walking-outside#ixzz4bItMghzK