Bacteria on the skin can both protect against atopic dermatitis and aggravate its symptoms

Inflammatory bowel disease is already treated by transferring gut microbes from healthy individuals to patients. It may also become possible to treat diseases and damage of the skin by improving the composition of the skin microbiota.

Atopic dermatitis is a chronic skin disease which most often develops in childhood and appears as dry, red and itchy rashes, while psoriasis is a chronic rash that usually only develops in adulthood and manifests as well-defined scaly patches. Both diseases result in a markedly impaired quality of life.

For the time being, it is not known why certain people develop atopic dermatitis or psoriasis while others do not, but both genes and environmental factors play a part. Micro-organisms of the skin are most likely an important link in the interaction between the external environment and the immune system of the skin.

Thousands of microbes – bacteria, fungi and viruses – live on healthy skin, and their composition varies by age, skin area and individual. Most skin bacteria belong to what is known as the normal flora. In other words, they are not pathogens but tasked with limiting the growth of pathogenic bacteria.

“The diversity and balance of the skin and gut microbiota have a significant effect on our health. Recent research demonstrates that microbes on the skin can both protect against diseases and help the skin heal faster,” explains Professor Harri Alenius.

Alenius coordinated MAARS, an extensive research project funded by the EU, which examined the significance of skin bacteria to atopic dermatitis and psoriasis. The University of Helsinki and Karolinska Institutet were among the central contributors to the project.

Staphylococcus aureus is a typical pathogenic bacterial species found on the skin, often invading rash sites in atopic dermatitis.

The findings of the MAARS project, recently published in the Nature Communications journal, demonstrated that S. aureus is much more prevalent in atopic rashes than on healthy skin. At the same time, the amount of Lactobacillus, Cutibacterium, Finegoldia and other health-promoting bacterial species decreases. Another finding was that the abundance of S. aureus and the toxins and metabolites produced by the bacteria had an effect on the support structure and defence mechanisms of the skin.

In the case of psoriasis, the composition of the skin microbiota had changed without any specific bacterial species prevailing at the rash sites.

“At the moment, we don’t know much about the role of micro-organisms found on the skin in the onset of skin diseases. These new findings help to understand the mutual interaction of the skin microbiota and the body in terms of disease mechanisms, which enables the development of novel therapeutic methods,” says Docent Nanna Fyhrquist, the principal author of the article.

Inflammatory bowel disease is already treated by transferring normal micro-organisms from the gut microbiota of healthy individuals to patients. The researchers believe it may also become possible to treat chronic inflammatory skin diseases by creating conditions on the skin that promote the abundance and balance of health-promoting microbial communities.

The clinical material originating in Finland used in the MAARS project was coordinated by Professor Annamari Ranki and Professor Antti Lauerma from the University of Helsinki and the Skin and Allergy Hospital (Helsinki University Hospital). Professor Harri Alenius and Docent Nanna Fyhrquist are participating in the Human Microbiome research program (HUMI) at the Faculty of Medicine, University of Helsinki, in addition to which they work at Karolinska Institutet.

For more information:

Professor Harri Alenius, University of Helsinki and Karolinska Institutet

Tel. +358 50 4489526, email:

Alenius Lab

Docent Nanna Fyhrquist, University of Helsinki and Karolinska Institutet

Tel. +358 50 314 7944, email: 

Professor Annamari Ranki, University of Helsinki and HUS

Tel. +358 400 875761, email:

Professor Antti Lauerma, Helsingin yliopisto ja HUS

Tel. +9  471 86304, email:

Reference: Nanna Fyhrquist & al. Microbe-host interplay in atopic dermatitis and psoriasis. Nature Communications.

MAARS (Microbes in Allergy and Autoimmunity Related to the Skin)