Effect of a forest bathing trip on natural killer (NK) activity (a) and the number of NK cells (b). Columns: Before values obtained before the trip, Day 1 values obtained after the first day of the trip, Day 2 values obtained after the second day of the trip. Data are presented as the mean ± standard deviation (SD) (n = 12). *P < 0.05, **P < 0.01, significantly different from before the trip, #
P < 0.05 significantly different from day 1 by paired t test. Cited from Li et al.