Take a mud bath! It cures you from diseases

Microbiologists are studying children, dogs and mice to unearth the beneficial effects of bacteria in soil.

We don’t miss tuberculosis, typhoid fever, or any number of terrible infectious diseases that were common before more hygienic and healthy lifestyles were adopted. But excessive hygiene has also been derided as the culprit for afflictions such as asthma, allergies and other dysfunctions of the immune system.

However, the “hygiene hypothesis” formulated by David Strachan, British professor of epidemiology in the late 1980s, appears to be wrong, says Lasse Ruokolainen, docent of ecology. According to Strachan, humans need pathogenic viruses to train their immune systems.

Academy Research Fellow Ruokolainen posits that the new afflictions plaguing the Western world have not been caused by the eradication of many infectious diseases, and that allowing them to return would not solve our modern problems.


Lasse Ruokolainen heads the research project formerly led by esteemed biologist Ilkka Hanski, which is seeking a better explanation for the increase in chronic inflammatory diseases. The ideas from the project have given form to a biodiversity hypothesis, which has already accrued significant supporting evidence.

The hypothesis describes heroic soil bacteria which humans collect from the first moments of their lives to be friendly helpers … or fail to collect.

Bacteria from the soil make their way into the body through the skin, respiratory system and mouth. The research, initiated by Ilkka Hanski and MD Tari Haahtela, has focused on a microbe called Acinetobacter Iwoffii. The microbe kept cropping up as the researchers compared cohorts of people with different lifestyles: people from Finnish Northern Karelia compared with people from Russian Karelia, Finnish babies with Estonian babies and urban Finns with people from the Finnish countryside.

In all of these cases, the group following a more rural lifestyle had a larger variety and greater number of microbes from the Acinetobacter genus. This same difference can even be found between dogs from the city and dogs from the countryside.

A similar study was conducted by collecting bacteria samples from the skin of children in kindergartens in suburban areas and central Helsinki, and particularly children in kindergartens with an outdoor nature theme. The skin microbiome of children in the nature kindergartens was the most diverse by a clear margin.


The amount of Acinetobacteria on the skin seems to correlate with the amount of inflammation-reducing proteins in the blood. Tests on mice indicate that Acinetobacteria can promote the secretion of interleukin-10, a key anti-inflammatory agent. At the same time, they restrict the formation of the signal molecules that promote inflammation, states Ruokolainen.

 “This results in a balanced immune response. Mice living in dirt have a better immune response than laboratory mice. Similarly, Russians have a more balanced immune response than Finns, as do healthy Finns when compared with Finns who have allergies.”

Should we be looking to mud baths to cure our new national afflictions instead of contracting infectious diseases? Ruokolainen thinks so. When the researchers exposed allergic mice to an allergen, mice whose skin had been treated with Acinetobacteria fared better than others. The healing effect of the bacteria that was applied to the skin was apparent both in the lungs and in the immune response.

However, the beneficial effects of the bacteria are not yet fully understood. The immunologists in Ruokolainen’s research group are studying the ways the bacteria influence their host, while doctors from the Hospital District of Helsinki and Uusimaa and the National Institute for Health and Welfare are surveying the phenomenon from a perspective of national health.

Extinction is unhealthy

According to the biodiversity hypothesis, epidemics of “new” illnesses have to do with the erosion of biodiversity. “As an increasing number of people live in cities, we begin to lose both access to and contact with nature,” Ruokolainen says.

Humans will be exposed to a limited selection of microbes, leading to a bacterial imbalance which can disrupt the immune system. This means that when there is an extinction event, it will lead to an asthma event among humans.

The creation of the body’s microbial networks begins in utero, based on the bacteria the expectant mother is exposed to. “But it is difficult to determine how important a particular stage of life is, as we are yet to complete comprehensive monitoring studies.”

We have many questions. Is it crucial to be exposed to nature at a particular age? And how much contact with nature is necessary? 

This article was published in Finnish in the Y/06/17 issue of Yliopisto magazine.

Get your hands dirty

Researchers are currently trying to improve the immune systems of children in kindergarten – and it seems that they have literally unearthed a solution.

 “We’ve brought dry peat, transferable lawn, planting boxes and peat blocks for activities to the yards of the participating kindergartens in Lahti, Tampere and now Espoo,” describes post-doctoral researcher Riikka Puhakka from the ADELE (Autoimmune Defence and Living Environment) project which studies the impact of the environment on health.

The researchers hope to find out how contact with living nature influences children and the microbes in their bodies.

 “We’ve found in the kindergartens that dry peat and grass encourage the children to be more mobile and to play without toys. It’s much nicer to crawl around on grass than it is on concrete or sand.”

The ADELE researchers have yet to gain results on whether the children in the participating kindergartens have increased the diversity of their microbiomes through the study.

Another study focuses on the microbes living on the children’s skin. Jenni Lehtimäki, a researcher in Lasse Ruokolainen’s research group, participated in an as-yet unpublished study which compared five-year-olds in outdoor nature kindergartens with those in highly urban kindergarten environments and in typical Finnish kindergartens which are adjacent to some natural areas.

 “The microbiome on the skin of the children in the nature kindergarten was clearly the most diverse.”

The difference between the nature kindergarteners and children in typical kindergartens was notable, as the environments of the kindergartens are ultimately not radically different.

 “We know that parents of children in the nature kindergartens are more nature-conscious, and the care concept emphasises being and playing outdoors in nature. For the biodiversity of the natural environment to be beneficial, frequent contact is necessary,” states Lehtimäki.

The group found no difference in the likelihood for allergies between the different kindergarten types. Lehtimäki believes that the onset of allergies is linked to even more complicated mechanisms.

Text Mikko Pelttari