Time in Nature

What it is

Time in nature means spending time in parks, woodland, forests and gardens, whether walking, sitting or simply being there. Forest bathing (shinrin-yoku) is one structured form, such as a three-hour guided walk [1]. Studies measure exposure in three ways: how much green space surrounds a home, usually from satellite images of vegetation [2]; time spent in real green settings [3]; and simulated nature, such as virtual reality or recorded forest sound [4][5].

How it might work

Proposed, not established: nature may calm the body's stress response, which trials measure through cortisol and heart rate [6]. Quieter, less polluted settings may explain part of the effect; a park walk lowered cortisol more than a walk on an urban street in one trial of heart patients [7]. Some researchers suggest natural settings help restore attention after mental effort [8]. For immune measures, tree chemicals called phytoncides (such as alpha-pinene and beta-pinene) are a proposed contributor: they were detected in forest air but not city air in the studies, and in the lab they raised the killing activity of a human natural killer cell line [9][10].

What the research says

Stress. Across 36 randomised trials of 2,925 people, portable digital nature experiences lowered stress (g = −0.51; 95% CI −0.73 to −0.28) [11]. Real outings also helped: in a randomised crossover trial of 42 adults, three hours of hiking outdoors or indoors lowered salivary cortisol more than sitting [12]. Across eight forest-bathing studies, cortisol was about 0.05 µg/dl lower after forest time than after urban time, with wide variation between studies and a possible placebo effect [13]. A forest-therapy meta-analysis of 25 studies (1,876 people) also found lower psychological stress (SMD −0.71; 95% CI −0.89 to −0.53), though variation between studies was high and the authors rated the certainty moderate [14]. In a trial of mothers and infants, walks in nature and in cities both reduced stress, and the setting did not make a significant difference [15].

Blood pressure. Across 21 studies of 2,270 urban residents, forest therapy lowered systolic pressure by 3.44 mmHg (95% CI −5.74 to −1.14) and diastolic pressure by 3.07 mmHg (95% CI −5.59 to −0.54) compared with urban controls. The studies differed widely, and the prediction intervals include zero, so an individual may not benefit [16]. In a cohort of 164,853 Guangzhou schoolchildren followed for three years, more greenness around home and school was linked to lower blood pressure and a 2.7% to 7.6% lower risk of hypertension [17]. In people with cardiovascular conditions, nature-based programmes lowered diastolic pressure by 3.73 mmHg (95% CI −7.46 to −0.00), with moderate to high risk of bias [18].

Mood and anxiety, short term. Across 36 randomised trials, portable nature experiences lowered anxiety (g = −0.67; 95% CI −1.01 to −0.33) and depression (g = −0.26; 95% CI −0.51 to −0.01) [11]. Across 15 randomised trials of exercise in urban green spaces (980 adults), mental health improved moderately (SMD −0.40; 95% CI −0.56 to −0.25), with low variation between trials [19]. A review of forest bathing studies with 3,554 people found reduced symptoms of depression and anxiety [20]. The same 25-study meta-analysis found falls in depressive symptoms (SMD −0.68; 95% CI −0.86 to −0.50) and anxiety (SMD −0.77; 95% CI −0.97 to −0.57), with certainty rated low for these outcomes [14]. A 2026 review of 11 forest-bathing studies found similar short-term effects on tension-anxiety and low mood but rated the certainty very low [21]. In a trial of 37 adults with major depression, one 60-minute walk in nature lowered negative mood more than an urban walk (p = .047) [22]. Not every trial agreed: 56 healthcare workers who took a three-hour forest bathing walk did not show a significant change in burnout scores, although most described less stress [1].

Immune function. Several small studies found that forest trips raised natural killer (NK) cell activity, the number of NK cells and the levels of anti-cancer proteins inside them [23][9]. In 12 men on a three-day forest trip, 11 of 12 had higher NK activity afterwards, about 50% higher on average [23]. A matching city trip did not raise NK activity, and the forest increase lasted more than 7 days [9]. Thirteen nurses showed the same pattern after a three-day trip [24], and a single day trip with two two-hour walks raised NK activity for 7 days [25]. Phytoncides are a proposed explanation: in 12 men who slept three nights in hotel rooms where hinoki cypress oil was vaporised, NK activity rose and urine stress hormones fell [26], and a randomised trial of 55 gynaecological cancer survivors found that eight weeks of daily phytoncide-scented rest sessions increased some NK cell measures and lowered stress [27]. In the lab, phytoncides increased the activity of a human NK cell line [10]. In a small randomised crossover trial, 30 men at risk of COPD who took a guided day trip to a cypress forest had lower blood CRP and IL-6 than after a matched city walk [28]. A systematic review of 13 studies found most reported improvements in NK measures and called for more randomised trials [29]; a second review of 33 studies found positive signals but weak study designs [30]. The NK measures are lab markers: the studies did not test whether people got fewer infections [29].

Depression risk over time. In a meta-analysis of observational studies, each 10% more green space around the home was linked to lower odds of depression (OR 0.963; 95% CI 0.948 to 0.979). The link to anxiety was not significant [31]. A 40-year birth cohort of 1,265 New Zealanders found a 12% lower risk of depressive symptoms per standard deviation more greenspace in adulthood [32]. Other cohorts found no link: among 46,786 Australians, green space was not linked to physician-diagnosed depression or anxiety [33], and among 16,189 middle-aged and older Europeans it was not linked to depressed mood [34]. A cohort of 6,772 pregnant New Zealand women also found no link to antenatal depression [35].

Long-term health. A 2018 review of 103 observational and 40 intervention studies found that more greenspace was linked to lower all-cause mortality (0.69; 95% CI 0.55 to 0.87). The authors describe several of the pooled analyses as limited by poor study quality and high heterogeneity [36].

Attention. Results are mixed. In 167 seven-year-olds, time in green school spaces did not improve attention more than time in grey spaces [8]. In a trial of 45 employees, selective attention improved more than in controls after two-hour nature sessions twice a week for three weeks (p = 0.045) [37]. In a cohort of 13,594 middle-aged women, more green space was linked to a small gain in psychomotor speed and attention (0.05 standard units) [2]. In a cohort of 742 Canadian adolescents, more childhood greenspace was linked to less inattention (β = −0.14) [38].

Doses used in studies

These are the doses used in the studies above, not recommendations. Single sessions in the trials ranged from 6 minutes of virtual woodland video [39] and a 20-minute virtual or real nature session [4] to a 60-minute walk [22] and a three-hour hike [12]. A three-day bamboo forest programme used 15 minutes of viewing and 15 minutes of walking each day [3]. Mothers in one trial walked for 45 minutes in each setting [15]. In a 2025 review of exercise in green spaces, the largest effects came from programmes under 12 weeks, sessions of 20 minutes or less, and at least three sessions a week [19]. In a forest-therapy meta-analysis, programmes of 20 minutes or more lowered blood pressure and cortisol more than shorter ones [16]. For immune measures, the classic forest trips were three days and two nights with two-hour walks [9][24]; a single day trip with two two-hour walks also raised NK activity [25]. One review reported the rise could last more than 30 days and suggested a forest visit about once a month might keep NK activity higher [40]. Phytoncide exposure alone was tested as three nights of vaporised hinoki cypress oil in a hotel room [26] and as one-hour scented rest sessions five days a week for eight weeks [27].

Safety and interactions

Side effects were rarely recorded. One trial of older adults reported no adverse events after a single 20-minute nature session [4]. Outdoor time carries real hazards. In a survey of 212 hill runners in Scotland, 82.5% reported at least one tick bite in the past year, and most rarely wore leg cover; regular leg cover was linked to lower odds of a bite (OR 0.35; 95% CI 0.13 to 0.89) [41]. Among 159 North Carolina outdoor workers followed for two years, 40 tick-borne infections occurred, and 38 of them were subclinical [42]. Among 175 outdoor day labourers, 54.9% had at least one sunburn in the past summer and 62.9% reported symptoms of heat illness [43]. These are workers, not recreational walkers, but the sun and heat risks apply to both. For people with pollen allergy, pollen counts can trigger symptoms, and the trigger level varies by pollen type and by person [44].

The studies read here did not report upper limits, interactions with medicines, or outcomes in people with kidney or liver disease or bleeding disorders, so these remain unknown. The trial in pregnant women read here used a virtual green-space video, not outdoor time [45].

Caveats and open questions

Many trials measured effects straight after a single session, so it is unknown whether benefits last [4]. Cortisol and blood pressure are markers, not diseases, and a change in them does not prove a change in health [16]. Expectation may play a part: the forest-bathing review notes that anticipated placebo effects may matter [13].

The immune findings are early. The classic trips had 12 or 13 participants and measured lab markers, not illness [23][24][29]; in the COPD crossover trial, fibrinogen fell after both the forest and city walks, so not every marker moved for the forest [28]. A 2026 meta-analysis of forest-bathing studies rated the certainty of the psychological effects very low [21], and a 2017 review of the six available RCTs found every one had high risk of bias and judged the evidence insufficient for clinical guidelines [46].

Settings differ. In a 2025 trial, forest sounds improved mood and cognition compared with industrial sounds, but not cortisol, heart rate or blood pressure [5]. Virtual nature and real nature are not always equal: in one trial, real nature improved positive mood but not attention, while a virtual nature video improved attention [4].

The evidence is weak overall. A 2024 Navigation Guide review of 113 studies on nature and mental health during COVID-19 rated the evidence 'very low' for all outcomes, with high risk of bias in many studies [47]. Observational cohorts can show association but not cause, and they disagree on depression [33][34]. Attention results are mixed [8].