The objective of this pilot randomized controlled trial is to evaluate the efficacy and acceptability of self-help forest bathing on depression, anxiety, and stress in the Hong Kong adult population.

Prior to all study procedures, eligible participants will be required to complete an online informed consent form (with telephone support). Around 80 eligible participants aged between 18 to 65 years old with at least a mild level of depression, anxiety, or stress symptoms will be randomly assigned to either the self-help forest bathing intervention group (FB group) or the waitlist control group (WL group) in a ratio of 1:1.

Participants in the FB group will receive forest bathing guidance via an in-house smartphone app. The WL group will be asked to maintain their typical activity in week 1-7. This group will receive the guide upon trial completion in week 8.

The outcomes of the interest will include generalized anxiety symptoms, depressive symptoms, insomnia symptoms, wellbeing, health-related quality of life, functional impairment at baseline (week 0), immediate (week 7), and 1-month post-intervention assessments (week 10). Treatment credibility and acceptability will be collected at baseline and immediately after the intervention.

Inclusion Criteria:

1. Hong Kong residents;
2. Aged between 18 to 65 years;
3. Meet the threshold for mild depression (score of >5 on the Patient Health Questionnaire 9 [PHQ-9], anxiety (>5 Generalized Anxiety Disorder 7 [GAD-7]), or stress (>15 on the Depression, Anxiety, and Stress Scale [DASS-21] stress subscale, after multiplying score by 2);
4. Able to read and understand Chinese and type in Chinese or English
5. Have an Internet-enabled mobile device (iOS or Android operating system)
6. Willing to provide informed consent and comply with the trial protocol

Exclusion Criteria:

1. Received psychotherapy for depression, anxiety and stress in the past 6 months;
2. A change in psychotropic drugs or over-the-counter medications that target depression, anxiety, and stress within 2 weeks before the baseline assessment.
3. Patient Health Questionnaire-9 (PHQ-9) item 9 score > 2, indicating a moderate level of suicidal risk that requires active crisis management (referral information to professional mental health services will be provided);
4. Currently participating in another intervention study that may potentially affect mental health;
5. Self-disclosure of having unsafe health conditions for which physical activity was contraindicated by physicians;
6. Self-disclosure of any psychiatric, medical, or neurocognitive disorder(s) that makes participation unfeasible;
7. Pregnancy;
8. Hospitalization.