06/08/2026
Spending time in a forest does more than calm your mind. It may directly strengthen your immune system, through an invisible gift the trees themselves provide.
Trees and plants release airborne compounds called phytoncides, which they produce to protect themselves from insects and microbes. Research on forest bathing has found that breathing in these compounds is associated with measurable increases in the activity and number of natural killer cells, a type of immune cell that helps defend against infections and abnormal cells.
Remarkably, studies have found that the immune-boosting effects of a forest visit can persist for days afterward. Some research suggests that a few days spent in a forest environment raised natural killer cell activity for over a week.
This adds a fascinating dimension to what we already know about nature and health. Time among trees lowers stress hormones and blood pressure, and now we see it may also fortify the body's defenses at a cellular level.
As a physician, I find this a beautiful illustration of how deeply connected we are to the natural world. We did not evolve in sealed rooms. Our bodies respond to forests as to a kind of medicine.
You do not need a wilderness expedition. A wooded park, a tree-lined trail, a green space rich with plants, all offer a version of this gift.
When could you spend some unhurried time among trees this week, breathing deeply?
