Authors of this article (2013) review studies to support their idea that plants contribute to the indoor microbial ecosystem, affecting human health and well-being.

Majority of our lifetime is spent indoors  – home, workplace and public buildings. The microbial communities of indoor environments are therefore an important component of everyday human health, acting both as a healthy microbial exposure as well as pathogens and allergens. Humans have a very high emission rate of ~106 bacteria per person-hour: this means that indoor environments are consisted highly of human associated microbes.Ffor buildings such as hospitals, this is troublematic, as they are more easily concentrated with patient-associated microbes. The risk of dying because of infections caused by these bacteria is the leading cause of death in the hospitals of developed countries, and the risk of infections in European ICUs has been reported to be 45 %. Indoor microbiome is also involved in the development of sick building syndrome (SBS), which causes symptoms that are associated to spending time in a certain building, possible leading to inability to be in that space at all.

In addition to humans, indoor microbes originate from pets, the buildings itself and the outside air. So far houseplants have not been considered to have a major impact except by one study (Burge et al. 1982). The authors provide further support for the theory of plants being an important source for a beneficial microbial biodiversity:

1. The psychological and cognitive effect of plants is well documented, as well as their capacity to improve indoor air quality. This is not only due to the filtering capacity of plant leaves, but their root microbiome as well.
2. Plant DNA is frequently detected as a major component in all indoor microbiomes, though is often neglected. Pollen and seeds are densely colonized by microbes and dispersed into the air, thus providing microbiome exchange.
3. Typical plant bacteria are found from the indoor air and are transmitted in several ways.
4. There is an interplay between plant microbes and indoor microbiome, as an imbalance of microbes and their hosts can have bad consequences such as infections.
5. Closely related microorganisms can exist in different microbiomes.

Based on existing studies, authors speculate that:

• Enclosed environments are shaped by human influence and human associated microbes
• Hence, microbial diversity is altered and reduced compared to outside environment. This is known to facilitate dominant proliferations of certain strains, causing possible negative effects to human health.
• To increase microbial diversity indoors, simply opening windows instead of using air-condition, and using potted plants as a source of microbial biodiversity to provide possibly beneficial microorganisms.