Spending time in a forest—through the Japanese practice of “forest bathing”—has been found to significantly elevate both the number and activity of natural killer (NK) cells, key components of the body’s cancer-fighting immune system.
Multiple studies report up to 80% increases in NK cell activity after day trips to woodland environments compared to urban settings, with stronger, more sustained effects lasting up to a month after forest exposure . This boost likely contributes to enhanced elimination of tumor cells and improved immune surveillance.
Scientists attribute these benefits to a powerful combination of factors. Forest air contains phytoncides—natural fragrant compounds like pinene emitted by trees—that have been shown in laboratory settings to directly stimulate NK cells.
Meanwhile, visiting forests also reduces cortisol—a stress hormone known to suppress immune function—while exposing us to beneficial environmental microbiota. Together, these effects point to a simple yet effective way nature may help strengthen the body’s defenses through controlled yet impactful environmental exposure .
Source: National Library of Medicine
