Research, though, suggests there's something to be said for reaching out to touch the trees, shrubs and soil I usually walk past. Mira Grönroos, an ecologist and nature-health researcher at the Finnish Environment Institute, asked people to rub their hands with soil, peat and moss for 20 seconds as part of an experiment. She found that the abundance and variety of microbes on their skin increased, even after they rinsed their hands with tap water. "To the naked eye [their hands] looked clean," she says, "but the change was so huge".