Being in a forest for a little while might help lower your stress hormone levels a bit, compared to being in a city — it’s like nature gives your body a little calm-down break.

A randomized crossover trial where the same group of healthy adults is exposed to a forest environment for 90 minutes and then to an urban environment for 90 minutes (order randomized and counterbalanced), with salivary cortisol measured immediately before and after each exposure, controlling for time of day, physical activity, and prior stress exposure.

A prospective cohort study tracking a group of urban-dwelling adults over 4 weeks, measuring salivary cortisol levels after each of three 90-minute forest visits and three matched urban visits, with cortisol sampled at standardized times to assess within-person changes across repeated natural vs. urban exposures.

A meta-analysis pooling data from all published randomized or quasi-experimental studies comparing forest vs. urban exposure on salivary cortisol, using standardized mean differences, with subgroup analyses by exposure duration, forest type, and baseline stress levels.

A case-control study comparing individuals who regularly spend time in forests (cases) with matched individuals who do not (controls), measuring baseline and post-exposure cortisol levels after a standardized 90-minute nature or urban walk.

A cross-sectional study measuring salivary cortisol levels in individuals immediately after they have completed a forest walk versus those who have completed an urban walk, with no prior exposure history controlled.