Phytoncides: What They Are and What the Research Actually Shows

Phytoncides are the aromatic compounds that trees and plants release to protect themselves from insects, bacteria and fungi. Pine trees are among the plants that produce them, and alpha-pinene and beta-pinene are two of the best known. They are a big part of why a pine forest smells the way it does. Researchers have studied what happens when people breathe forest air rich in these compounds. The results are interesting, but early.

What the research found

In small studies led by Qing Li at Nippon Medical School, healthy adults who spent two or three days in a forest showed higher natural killer (NK) cell activity in blood tests, and the rise lasted at least seven days. In a follow-up, 12 men slept in hotel rooms with vaporised tree oil and showed a similar rise.

What it does not show

A short-term change in an immune marker is not the same as preventing illness. These studies were small, mostly in healthy middle-aged adults, and did not measure disease. A systematic review of forest-bathing research rated the included studies at high risk of bias and said the evidence is not strong enough for clinical guidelines.

Antimicrobial, for the tree

Trees make phytoncides to defend themselves against microbes and insects. That describes what they do for the tree. It does not mean that a skincare product containing pine leaf protects your skin or body from infection.

Where the evidence is stronger: time in the forest

Most of this research comes from forest bathing, or shinrin-yoku: spending slow, unhurried time among trees, a practice promoted in Japan since the 1980s.

A 2021 review of 11 systematic reviews found benefits for stress, blood pressure and mood, including depression and anxiety scores, while rating confidence in most of those reviews as low. A meta-analysis found that forest bathing lowered cortisol, a stress marker, in the short term, and noted that people's expectations may play a part. Phytoncides are only one part of the experience: the quiet, the green, the slower pace and the walk itself all count.

Why pine leaf is in every SOLYPH product

SOLYPH started with this forest story. Every formula is built on pine leaf water, steam-distilled from pine needles from the forests of Pyeongchang, Korea, and we use it as a fresh-scented, hydrating base. We don't claim that putting it on your skin gives you the effects of a day in the woods. For that, go for a walk. Our products are not tested on animals.