Forest Therapy and Mindfulness for Highly Sensitive Persons

This is a multicenter, randomized, parallel-group interventional study in adults with high sensory-processing sensitivity confirmed using a validated instrument. Participants are randomized 1:1 to one of two study arms at study entry and remain in their assigned group for the duration of the study.

Intervention delivery is standardized across participating sites through facilitator training and a predefined session manual. The experimental arm consists of structured sessions conducted in forest environments and includes guided walking, mindfulness-based practices, and structured sensory awareness activities, with facilitated group reflection. The active comparator arm consists of structured indoor group activities designed to match the experimental arm in duration, group interaction, and facilitator contact, without exposure to forest or outdoor natural environments.

Study procedures and assessment schedules are predefined in the protocol and implemented in accordance with applicable ethical requirements and Good Clinical Practice guidelines.

• Forest Therapy + Mindfulness + Psychotherapy (Behavioral): Participants will undergo a approximately 22-week program with 4.5 hours weekly in forest settings. Each session includes: A 2-hour guided walk with scheduled rest/hydration breaks Mindfulness meditation (20-30 minutes) Discussion/reflection segment (\~20 minutes) for participants to express sensations, experiences, or doubts A psychotherapeutic component focused on emotional processing and cognitive regulation Sensory observation (5-10 minutes) of forest stimuli (olfactory, auditory, tactile, visual) Post-session journaling capturing emotional and sensory feedback Monitoring of environmental parameters (temperature, humidity, wind, estimated phytoncide levels) Standardized facilitator training and session protocols to ensure consistency across sites This protocol is distinguished by integrating forest immersion, mindfulness, psychotherapy, and sensory training in a unified intervention tailored for Highly Sensitive Persons (HSP).
• Behavioral: Indoor Sensory Control (Art and Aromatherapy) (Behavioral): Structured indoor sensory-based group sessions delivered weekly over approximately 22 weeks. Activities include creative tasks, guided aromatherapy, and sensory-focused exercises conducted in indoor, non-forest environments. Sessions are designed to match the experimental intervention in duration, structure, facilitator contact, and social interaction, according to a predefined protocol.

Primary outcomes

• Change in Perceived Stress Score (PSS-10) From Baseline to End of Intervention [Baseline to end of intervention (approximately 22 weeks)]: Measure the difference in total score on the Perceived Stress Scale (PSS-10) between baseline and the end of the intervention. PSS-10 comprises 10 items scored 0-40, with higher scores indicating greater perceived stress.

Secondary outcomes

• Change in Psychological Well-Being Score (WHO-5) From Baseline to End of Intervention [Baseline to end of intervention (approximately 22 weeks)]: Measure the difference in total score on the WHO-5 Well-Being Index between baseline and the end of the intervention. WHO-5 comprises 5 items scored 0-25, with higher scores indicating better well-being.

Sex: All, ages: 18 Years to 65 Years, accepts healthy volunteers

Inclusion Criteria:

* Age 18 to 65 years
* High sensory-processing sensitivity confirmed using a validated instrument (e.g., HSPS/Aron scale)
* Able to perform moderate physical activity (e.g., walking)
* Able to provide written informed consent

Exclusion Criteria:

* Severe psychiatric disorder or acute clinical instability
* Medical condition contraindicating moderate physical activity
* Use of medications with strong autonomic or neuroendocrine effects (e.g., high-dose systemic corticosteroids; selected beta-blockers)
* Recent participation in a structured mindfulness or forest-therapy program
* Pregnancy or unstable medical condition

• Results publication: Sánchez Hdz, Ana I. Forest Therapy and Mindfulness in Highly Sensitive Persons (HSP): Confirmatory Evidence from a Multicenter Randomized Controlled Trial with 6-Month Follow-up. Zenodo. DOI: 10.5281/zenodo.17361382. Available at: https://zenodo.org/records/17361382

• Ana I Sánchez Hdz, Principal investigator, IFM International Forest Medicine