Dirty hands protect people from immune-mediated diseases

Submitted on Mon, 07/02/2018 - 11:55
Likaiset kädet/ Kuva: Jenni Toivonen
Urban people are often alienated from nature and do not get exposed to nature’s microbial biodiversity. Too little microbial exposure has been suspected of causing allergies, asthma, type 1 diabetes, coeliac disease, and bowel diseases. Photograph: Jenni Toivonen

Even just two weeks of exposure can improve the diversity of microbiota of people living in the city

Heikki Hyöty/ Kuva: Jonne Renvall
According to Professor Heikki Hyöty, the immune system needs exercise, which is not available in the urban environment made up of asphalt. Photograph: Jonne Renvall

Text: Jaakko Kinnunen

A recent study shows that rubbing hands in woody soil adds to the diversity of skin and intestinal microbiota. In the light of current research, extensive microbial exposure protects people from many immune and autoimmune diseases.

“Our aim was to find a way to restore people’s lost connection to nature,” says Professor Heikki Hyöty from the University of Tampere in Finland.

The study was based on the biodiversity hypothesis. If the immune defence system does not get enough exercise, it may not be able to distinguish really harmful agents from harmless predisposing factors. For example, an allergy results when the immune defence system attacks harmless pollen. The body’s immune system may also attack the normal intestinal microbes, which may lead to the development of chronic bowel diseases.

“If the body does not get enough microbial exposure, the ability of the immune system to control excesses is compromised. This is what the biodiversity hypothesis means,” Hyöty says.

Researchers from the University of Helsinki and Tampere University of Technology (TUT) also participated in the study. Hyöty especially praises Docent Aki Sinkkonen from the University of Helsinki and Professor Juho Rajaniemi from TUT.

Participants rubbed their hands
with a product made from woody soil

In the study, fourteen city dwellers rubbed a powder of woody soil into their hands three times a day for two weeks. They were instructed to wash their hands with tap water without soap.

The powder was a standardised and versatile blend of soil and herbal ingredients, which was optimised for its microbial diversity to give powerful stimulation to the immune system. For example, mosses, leaves fallen from trees and mulch were ground for the powder.

“The plan was to make the microbial diversity as great as possible. The participants were given a large amount of natural bacteria and viruses to which their immune system reacted,” Hyöty explains.

The participants collected stool samples prior to exposure, at the end of the exposure period, and three weeks after exposure. In addition, they collected a swab from the skin of their arm. Blood samples were also collected at the end of the experiment.

The study found that only two weeks of exposure to microbes could significantly improve the diversity of the microbiota of people living in the city.
“It is difficult to get similar results with probiotics, which have also been studied in the context of the biodiversity hypothesis,” Hyöty says.

The asphalt environment
is not good for people

Especially in the rich Western countries, normal everyday life has significantly changed in a short time: people live in blocks of flats with yards made of asphalt, hands are washed with soap several times a day, and homes are cleaned with various chemicals.

“The immune defence system needs exercise, which it does not get in the asphalt environment,” Hyöty says.

During the first year of life, versatile microbial exposure is particularly important. During that time, the immune system should get enough exercise to allow it to develop normally.

Too little microbial exposure has been suspected of causing allergies, asthma, type 1 diabetes, coeliac disease, and many inflammatory bowel diseases, such as Crohn’s disease.

“These diseases are steeply increasing in all Western countries. The change is so fast that it cannot be due to genetic reasons. That is why the cause is likely to be found in the changed habitat,” Hyöty points out.

The result of the study supports the biodiversity hypothesis. With urbanisation, people need new ways to maintain their relationship to nature.
“We must remember that his was a pilot study, and further studies will be needed to find out whether exposure to woody soil can really prevent immune diseases,” Hyöty says. 


Nurminen N, Lin J, Grönroos M et. al: Nature-derived microbiota exposure as a novel immunomodulatory approach. Future Microbiology, Vol. 13, No. 7. https://doi.org/10.2217/fmb-2017-0286