Does a city park also work?

Yes, with reduced effect. Bratman's research demonstrated effects from city parks too. Effect size is: natural forest > city park > city street. Parks with big trees, water, and soil are best. Even 30 minutes daily accumulates.

Instructor-led vs alone?

An instructor amplifies the "therapeutic" effect. Structured breathing, meditation, and curated trails produce larger drops in depression / anxiety scores. Alone, the physical benefits (cortisol, immunity) dominate. Recommend 1–2 instructor-led sessions to start.

Does it work in winter?

Yes. Phytoncide concentration peaks in summer, but conifer stands (Korean pine, pine, fir) release them year-round. Cold reduces parasympathetic activation, so shorter sessions (1–2h) still produce effects. Watch for frostbite and slippery surfaces.

Forest bathing — Korea's 51 national recreational forests, 30 years of Japanese shinrin-yoku data, phytoncides, NK cells, 24% cortisol reduction

Shinrin-yoku (森林浴, "bathing in the forest") was introduced as a policy term by Japan's Ministry of Agriculture, Forestry and Fisheries in 1982. Over the following 40 years, clinical evidence accumulated across Japan, Korea, Finland, and the US, and "forest therapy" now has a foothold as an adjunct treatment. Korea added forest-therapy provisions to the Forest Culture and Recreation Act in 2010, established the Korea Forest Welfare Institute, and launched the national Forest Therapy Instructor certification (2014–). Three core mechanisms: ① Phytoncides (volatile organic compounds released by plants) — NK (natural killer) cell activity +50%, immunity rises (Li et al., 2008, University of Tokyo). ② Natural soundscape and visuals — parasympathetic activation, cortisol -24%, heart rate down (Park et al., 2010 meta-analysis). ③ 1/f natural oscillation and green visual field → prefrontal rest, rumination down (Bratman et al., 2015, Stanford). Korea has 51 national recreational forests and 4 national forest-therapy centers (Yeongju, Cheongyang, Sanueum, Gombaeryeong). Two hours per week reduces depression and anxiety by an average of 30% over 4 weeks (Korea Forest Welfare Institute, 2022). No medication required — a near-zero-cost self-administered therapy accessible to urban dwellers.

1. 40 years of accumulated data

Japan's Ministry of Agriculture, Forestry and Fisheries launched the "forest-bathing for health" policy in 1982. Subsequent research by Prof. Li Qing of Nippon Medical School (2007–) established immunological effects, while Park Bum-Jin of Chungbuk National University (2010–) clinically demonstrated cardiovascular and psychological effects. Finland uses "Green Prescription" — doctors prescribe forests. The WHO published urban green-space guidelines in 2020 (≥9 m² per person).

2. 3 mechanisms

① Phytoncides

Volatile organic compounds (α-pinene, β-pinene, d-limonene) trees release to protect themselves from insects and microbes. Li et al. (2008), Tokyo: adults staying in a forest for 3 days showed NK-cell activity rise an average of 50%, with the effect persisting for 30 days. Anti-cancer proteins (perforin, granulysin, granzyme A / B) also increase.

② Parasympathetic activation

Park (2010), Chungbuk National University meta-analysis of 4 cities vs 4 forests: the forest group showed cortisol -24%, heart rate -6%, blood pressure -3.8 mmHg, HRV +13%. The autonomic nervous system shifts from "tension (sympathetic)" to "recovery (parasympathetic)".

③ Cognitive / affective effect

Bratman et al. (2015), Stanford: 90-minute nature walks vs 90-minute urban walks. The nature group showed reduced activity in the subgenual PFC (rumination circuit) and lower self-reported rumination. The urban walk had no effect. Exercise alone ≠ nature effect.

3. Korean forest-therapy infrastructure

Facility	Features
4 National Forest Therapy Centers	Yeongju (Gyeongbuk), Cheongyang (Chungnam), Sanueum (Gyeonggi), Gombaeryeong (Gangwon). Medical partnerships, resident certified instructors. 1–3 night programs.
51 National Recreation Forests	Nationwide, with lodging and "therapy forest" trails (5–10 km).
Urban therapy forests	Mudeung in Gwangju, Iljasan in Seoul Gangdong, Hwangnyeongsan in Busan — 60+ sites.

4. 4-week self-administered protocol

Week 1 — start in a city park

One 90-minute city-park walk per week (Namsan, Olympic Park, Seoul Forest, etc.)
Phone in airplane mode
No music — only natural sounds
Half your normal walking speed

Week 2 — peri-urban forest

Bukhansan, Gwanaksan, Dobongsan — peri-urban mountains
One 3-hour outing per week (including travel)
Sit by or touch a specific tree for ~5 min

Week 3 — 1 night at a national recreation forest

One weekend overnight
Find a nearby forest at the Korea Forest Welfare Institute website
Early-morning walk (phytoncide concentration peaks)

Week 4 — Forest Therapy Center program

2 nights at one of the 4 national centers
Programs with a certified instructor (breathing, meditation, trails)
Not covered by national insurance — ~150,000–250,000 KRW per night

5. Urban shortcut — "Green Hour"

If weekly mountain trips are hard:

30-minute daily park walk near work or home
Pick somewhere with big trees, water, soil if possible
Measurable change in 2 weeks (PSQI sleep, PSS stress)

6. Who benefits most?

Mild to moderate depression / anxiety (severe requires medication / therapy alongside)
Burnt-out workers
Chronic disease — hypertension, diabetes
Lowered immunity (frequent colds)
Urban residents with low physical activity

7. Cautions

For severe depression / suicidal ideation, do NOT use forest therapy alone — combine with medical treatment
Check for allergies (pollen, ticks) in advance
Summer: ticks, wasps, heat stroke
Winter hikes shorter; watch for frostbite

8. Getting it as a medical recommendation

There is no formal "forest-therapy prescription" in Korea, but psychiatry / integrative medicine physicians can recommend it as a form of "exercise prescription". Some company EAPs, occupational insurance, and the National Health Insurance Service's "Health-In" program offer linkages.