Do Terpenes Play a Role in the Stress-reducing Effects of a Forest Bathing Intervention?

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University of Washington




Monoterpene Exposure During a Forest Bathing Intervention


Behavioral: Forest bathing

Study type


Funder types



R21AT011242 (U.S. NIH Grant/Contract)

Details and patient eligibility


This pilot study evaluates the role terpenes play in the stress-reducing effects of a forest bathing intervention. Participants will participate in two interventions in random order: 1) terpene exposure and 2) no terpene exposure.

Full description

The investigators will use an individual-level crossover design in which each session is conducted independently and on different days. Participants will be outfitted with a powered air purifying respirator (PAPR) to selectively modulate exposure to a natural suite of forest-derived volatile organic compounds (VOCs) while present in forest environments. Each participant will undergo two forest bathing sessions, one in which VOCs are not filtered (treatment condition), and one in which they are filtered (control condition). Sessions will be separated by a 7-day washout period for each participant, and order will be counterbalanced. The investigators will estimate the average effect of treatment over 40 distinct treatment days against 40 distinct control/filtered days. The power and sample size calculations (N = 40) were determined using previous nature exposure studies of similar cross-over design. The study is adequately powered assuming the conventional targets of α = 0.05 and β = 0.80 with a 10% anticipated dropout rate, and including temperature, wind, and light variability during treatment days. The specific aim of this project is to 1) assess whether VOC inhalation regulates increases in the high frequency (HF) (ms2) component of heart rate variability (HRV) as the primary outcome (with decreases in blood pressure, heart rate, self-reported stress, and levels of inflammatory cytokines in serum included as secondary outcomes); and 1a) assess the degree of association of absorbed dose of seven forest-derived VOCs in serum (i.e., α-pinene, β-pinene, β-myrcene, ∆ 3-carene, d-limonene, β- caryophyllene, α-humulene) with these outcomes.


40 estimated patients




18+ years old


Accepts Healthy Volunteers

Inclusion criteria

  • 18 years and older
  • Non-smoker
  • Physically capable of walking for approximately 15-20 min from the study vehicle to the clinic and experimental locations.

Exclusion criteria

  • Pregnancy
  • Current or prior diagnosis of neurologic, hypertensive, psychiatric, respiratory disorder, or anosmia/hyposmia
  • Some types of medication.
  • Olfactory sensitivity threshold (assessed via UPSIT® test kit (Sensonics International, Haddon Heights, NJ)
  • Positive COVID-19 test

At enrollment, participants will complete a baseline survey on demographics, personality traits, and regular nature contact and perceptions. Study staff will also use the clinically-validated UPSIT® test kit (Sensonics International, Haddon Heights, NJ) to evaluate olfactory sensitivity and identify/exclude participants with undiagnosed smell loss.

Study staff will work with participants to schedule their forest bathing sessions and review instructions on how to prepare (e.g., by avoiding alcohol, marijuana, and certain foods, drinks, and household cleaning products with high terpene concentrations 24 hrs before their session).

Trial design

Primary purpose




Interventional model

Crossover Assignment


Double Blind

40 participants in 2 patient groups

Terpenes On
Experimental group
Forest bathing intervention with no filtration of terpenes from inhaled air ("terpenes on")
Behavioral: Forest bathing
Terpenes Off
Active Comparator group
Forest bathing intervention with filtration of terpenes from inhaled air ("terpenes off")
Behavioral: Forest bathing

Trial contacts and locations



Central trial contact

Gregory Bratman, PhD

Data sourced from

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