This Week In Wellness research from the University of Adelaide suggests that microbes in dust may help improve gut health and by extension mental health.

This contributes to a growing body of research linking time in nature with improved health outcomes. Especially from Japan where Forest Bathing or “shinrin-yoku”, which means “taking in the forest”, has been popular for decades and research has been done and benefits have been shown from microbes in the soil right through to scents from the trees. At the same time our urban environment has been linked with reduced health, including mental health disorders.

https://medicalxpress.com/news/2019-11-biodiverse-soil-linked-anxiety.html

https://www.sciencedirect.com/science/article/pii/S0048969719346753?via%3Dihub