A study has found children who are exposed to tree and weed pollen in urban environments are at increased risk of respiratory health problems, including asthma. While green areas in urban settings decrease exposure to air pollution, allow kids to be active, and offer positive contact to a diverse microbiota — which in turn may help the positive development of a child’s immune system — they can also lead to the development of childhood asthma. Thankfully, trees can help mitigate this effect to some degree, thanks to their canopy.