actinomycetes—which the human nose can detect at concentrations of
10 parts per trillion—and of course we harvest mold spores to make
critical antibiotics like penicillin. Dirt can heal: in two separate
experiments in England and the United States in 2007 and 2010, the
mice lucky enough to be exposed to a common soil bacterium,
Mycobacterium vaccae, performed better in a maze, showed less
anxiety and produced more serotonin, a neurotransmitter many
scientists think is associated with happiness.
To test the phytoncide theory, Li locked thirteen subjects in hotel
rooms for three nights. In some rooms, he rigged a humidifier to
vaporize stem oil from hinoki cypress trees, which are common in
Japan; other rooms emitted eau-de-nothing. The results? The cypress
sleepers experienced a 20 percent increase in NK cells during their
stay, and they also reported feeling less fatigued. The control group
saw no changes.
“It’s like a miracle drug,” said Li, when I interviewed him at his
university lab in Tokyo.
It sounds totally hokey, even unbelievable, that evergreen scents
—not unlike the thing that dangles from taxicab rear-view mirrors—
could help us live longer. But Li found similar results with NK cells
exposed to phytoncides in a petri dish. The cells increased, and so did
anticancer proteins and proteases called granulysin, granzymes A and
B and perforin, which cause tumor cells to self-destruct. It’s unclear
whether there’s something magical in the aromatic molecules or if the
smell simply makes people feel good, reducing stress. Li’s olfaction
theory is unconventional, but it contains some of that zen five-sense
wisdom. While American researchers are mostly showing people
pictures of nature or sending them out for loops around the campus
green, the ones in Japan are practically pouring it into every orifice.
Li, the chairman of the Japanese Society of Forest Medicine, uses
some of his insights in his own life. “In fact,” he said, “I use a
humidifier with cypress oil almost every night in the winter!” You