Biodiversity hypothesis suggests that two global megatrends, increasing global burden of chronic, non-communicable diseases and declining biological diversity on Earth are connected. The link between the two is hypothesized to be a decreasing exposure to beneficial environmental microbes that support development and function of immune system. Skin is open for microbial colonization from the environment, and a large proportion of skin microbes are transient. Skin and its microbiome are active both in local and systemic immune responses. These features make skin microbiome a potential link between living environment and human health. Urban environments provide homogenous microbial exposures enriched with common human skin bacteria, while rural and farming environments provide heterogenous microbial exposures. Active contact with soil or other natural elements shapes composition of skin microbiome relatively fast and living in greener environment impacts on microbial taxa found on human skin. These findings support the notion that surrounding nature and contact with it are influencing microbial communities on skin. Importantly, skin microbes originating from nature have been associated with immunoregulatory pathways and decreased risk on asthma and atopic diseases. Therefore, ongoing biodiversity decline and inadequate green areas in residential environments can limit human exposure to beneficial microbes. This chapter describes the history and current evidence of the biodiversity hypothesis, and represents related concepts including hygiene hypothesis, exposome and planetary health.