This article (2015) describes the results from multiple studies concerning the differences in the prevalence of allergies between the finnish and Russian Karelia. During the Karelia allergy study (1998–2004), it was noticed that allergic symptoms and diseases were systematically more common in Finnish children and adults than in their Russian counterparts: for example, sensitivity to birch pollen was 2 % in Russian and 27 % in Finnish Karelia. The differences have turned from non-existent to manifold for people born between 1940 to 1970.

The Finnish and Russian Karelia are adjacent, geoclimatically similar areas, where people share the same genetical background. The largest differences are in living conditions: on the Russian side people live in more simple conditions with cattle and domestic animals, self produced food and spring water. In general, there is a lot less built environment compared to Finnish towns. 

The studies found, that in Finland compared to Russia:

• Asthma was 5.5-fold more frequent: 8.8 % vs. 1.6 %
• Hay fever was 14-fold more frequent: 15.6 % vs. 1.1 %
• Eczema was 5-fold more frequent
• 43 % had at least one positive SPT reaction compared to 16 % among the Russian children

Atopic sensitization was inversely related to the amount of microbial components in house dust in Finnish children. Microbe-rich drinking water was strongly associated with the reduced risk for atopy in Russia. Genetics couldn’t explain the differences, but poor biodiversity did: there were major disparities between the Finnish and Russian house dusts both in microbial quantity and in diversity, which was much greater in Russia.

Loss of environmental biodiversity leads to reduced human microbiota (dysbiosis), immune dysfunction (poor tolerance), inappropriate inflammatory responses and finally symptoms and disease. We conclude that the epidemics of chronic inflammatory diseases, including allergy and asthma, are largely the result of reduced exposure to natural environments, changed diet and sedentary lifestyle.