A decrease in the amount of time spent in contact with the natural environment and changes in the population of microbes resident on the skin could be contributing to the increase in inflammatory disorders such as allergies.

To test these ideas, Ilkka Hanski at the University of Helsinki and his colleagues measured immune reactions to common allergens and the composition of skin microbes in 118 adolescents in eastern Finland. The team used the mixture of plants in the young peoples' gardens along with local land use as measures of biodiversity. They found that people living in areas of reduced biodiversity were more prone to allergies, and that allergic individuals had distinct populations of bacteria on their skin. Among healthy individuals, those with a greater abundance of the bacterial genus Acinetobacter on the skin produced higher levels of the immunoregulatory protein IL-10, which helps the body to tolerate harmless substances.

Loss of biodiversity could cause problems for public health as well as for the environment, the researchers suggest.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1205624109 (2012)