A study from Finland found that children's immune systems improved from only a month with regular time playing in the forest.

The study followed children ages three to five across 10 daycares. The 75 kids played in different environments: some had classic gravel yards while others took the kids to play in a natural forest everyday. Four daycares revamped their old gravel yards to be forest-like.—grass was rolled out, and heather and blueberry plants found in forests were added. Children were encouraged to garden. 

The microbiomes of the children's skin and guts were tested before and after a 28-day period. Over a month of exposure to the forested outdoors, the children's skin biomes became more diverse.

 They also saw an increase in T-cell count in the blood. Both of these findings are signs of a strengthened immune system. These quick changes impressed the researchers, but further studies will be needed to determine the exact causal mechanisms. Why is it that nature seems to benefit children's health? 

It seems that trees may help brain development and a forested environment boosts the immune system. Read more