Researchers are calling on cities to replace asphalt with forest-like plants in daycare centers in urban settings. Their study shows that children whose outdoor play areas were transformed in this way showed improved immune systems within a month. This simple change allowed their bodies to develop much more diverse microbes on their skin and in their intestines.


Numerous studies have reported that cities with well-connected green spaces allow their residents to practice regular physical and leisure activity, provide them with mental well-being (reduction of stress and symptoms of depression, etc.) and facilitate social contacts. Thus, cities that have them are likely to be home to a healthier population, with particularly notable beneficial effects for economically disadvantaged communities, children, pregnant women and the elderly. In this context, a team of researchers recommends “greening” all the more recreation areas dedicated to children.

These researchers, affiliated with several institutions in Finland and one in the Czech Republic, claim in the journal Science Advances that replacing asphalt in daycare play areas with natural vegetation can strengthen children's immune defenses. “Previous research has suggested that one of the reasons for the increased rates of autoimmune diseases in many parts of the world, such as inflammatory bowel disease, type 1 diabetes, multiple sclerosis , eczema and asthma, is the lack of exposure to elements that push the immune system of children to react ”, specifies the scientific team.

"The most exciting place in the yard for children"

The idea is that repeated exposure to natural elements such as dust, dirt and pollen during youth strengthens the immune system: this is the “hygienist hypothesis”. The researchers noted that children living in urban areas are most at risk of not benefiting from such exposure, which could explain their higher rates of autoimmune diseases. They therefore sought to test this theory by modifying one of the main environments in which these children play, namely the playgrounds in day care centers. They have been given permission to replace asphalt in several daycare centers in two of Finland's main cities.

This material has been replaced by sod dug from forest areas, forest shrubs, bushes and mosses. The children in the centers, 75 in total, were encouraged to play in these newly developed areas in their free time: they spent an average of 90 minutes a day there and were encouraged to play with the plants and the soil. “It was easy because the green area was the most exciting part of the yard for them,” Prof. Aki Sinkkonen, who led the study, told the Guardian. The researchers took blood samples from all participants, before the study and 28 days after, to analyze their immune system markers.

 A more diversified microbiota, guarantee of a good immune system

Although the study group was small, they believe their striking results warrant publication. After the study period, they noticed a significant increase in the skin microbiota (all microorganisms living in a given environment). Indeed, the diversity of microbes present on the skin of children was a third higher than for those who played in yards with gravel and was considerably increased in the gut. Blood samples also showed beneficial changes in a range of proteins and cells related to the immune system, including anti-inflammatory cytokines and regulatory T cells.

The researchers gave all the children the same meals every day and while they could not control the home environment, they claim that a significant change was observed despite varying domestic conditions which shows that the impact of this intervention was important. “Our study may pave the way for new preventive practices to stem the spread of autoimmune diseases around the world,” concludes Prof Aki Sinkkonen. Even if other scientific studies must prove the benefits of such a measure during infancy, they are already calling for pressure to be put on the public authorities for such changes to be made.