Wellmicro Lab Research: Tannin and Microbial Balance

Anyone who owns a pair of vegetable tanned leather shoes knows well that the comfort they offer cannot be reached by any other material. When the foot is in contact with leather treated with tannins, feet stay fresh, dry, and feel less tired.

At the end of the day, when you take off your shoes, there is no sign of the pungent and offensive odor characteristic of shoes with insides made of synthetic materials (like sneakers). And the next morning, the odor seems to have naturally disappeared, without the use of deodorizers.

We know that the odor is caused by bacteria lurking in your shoes (see the page“Foot odor – causes”). Does vegetable tanned leather have the ability to inhibit bacterial activity?

To scientifically confirm this theory, a team of Italian scientists conducted an interesting experiment, with truly surprising results.

* WellMicro, spin-off subsidiary of Alma Mater Studiorum – University of Bologna

Tannins, Skin Flora Mediators

The study was part of a large body of scientific research investigating the benefits of tannin and was aimed at providing a response to the following question: “Can the insole and the lining in shoes make it possible to select the types of bacteria present, to the detriment of those which produce odor?”

In Vivo Study: Vegetable Tanned Leather vs Synthetic Material.

The research was conducted on 15 volunteers (8 men and 7 women) between the ages of 18 and 65.

January 01, 2021
12 AM

Each participant was given a new pair of shoes (ankle boot style) to be worn continuously for a period of 28 days.

January 01, 2021
12 AM

Each pair was identical except for one detail: the left shoe had an insole and internal lining made of vegetable tanned leather containing a mixture of Chestnut and Quebracho tannins; the inside of the right shoe was made only out of synthetic material.

January 01, 2021
12 AM

A sample was taken from each shoe using a sterile swab, at 3 intervals of time, one at the beginning of the experiment, one after 14 days and one after 28 days.

January 01, 2021
12 AM

The swabs were then analyzed using a sequencer, an instrument capable of performing an analysis to determine the phylogenetic classification of the microbial population within the shoe,

January 01, 2021
12 AM

This particular study used Next Generation Sequencing (NGS) or parallel sequencing making it possible to sequence large genomes in a short period, literally in a matter of weeks.

January 01, 2021
12 AM


Upon the analysis of the swabs, the sequencer revealed that the left shoe and the right shoe had a significantly different bacterial population due to the different types of material used on the inside of the shoe, namely, vegetable tanned leather and synthetic material respectively.

In particular, the shoe with synthetic material supported the growth of those bacteria responsible for producing odor, among which, we found:






  S = lining and insole in synthetic material

  T = lining and insole in vegetable tanned leather containing tannins

= bacterium that does not cause odor


Download Wellmicro’s Research

I accept the terms of use for the copyright of Wellmicro research, which can be cited in studies, research, exhibitions or thesis, but not reproduced, either in whole or in part. For more information on the terms of use of the research, please send an email to info@tannins.org

Your data will be processed in compliance with the GDPR - General Regulations for the Protection of Personal Data. By clicking on "Send", you consent to the processing of data. For more information, see our Privacy Policy.

13 + 9 =

What Is a Sequencer

Up until a few years ago, there was only one way to study the behavior of bacteria: allow them to grow and then put them under a microscope.

The method is scientifically impeccable but the conditions in which the bacteria are cultured are unnatural: they are grown in a laboratory, an artificial environment with no interaction with other microorganisms or organic substances (unless there is human intervention).

Also, several types of bacteria cannot be grown in vitro and some environmental conditions cannot be replicated.

The invention of the NGS technique has changed the game by allowing microbiologists to identify microbial ecosystems in their totality directly from a sample taken from their natural environment, rather than from a laboratory culture source.

The result is a complete picture of the bacterial life and the interactions between different bacteria.

A Different Approach to the Study of Bacteria

Our body is home to trillions of bacteria that play a vital role in our health and perform beneficial functions. They are often referred to under the collective term “microbiota”.

For decades, these bacteria have generally been considered a negative presence, something to get rid of with soaps and disinfectants.

However, new biomedical technologies and instrumentation have led to unexpected discoveries: the problems are not caused by the presence of bacteria, but rather, by the action of a third factor that upsets their delicate natural balance.

Foot odor, which is caused by the metabolic activity of bacteria, does not manifest itself on bare feet or, if it does, it is very minimal; it is triggered however when the foot is placed in a shoe, an unnatural environment which negatively impacts on body temperature, breathability and humidity.

Therefore, the right solution to counteract the activity of bacteria inside the shoes is a natural substance that acts as a re-equilibrator of the skin flora, to restore, as much as possible, the natural conditions of the foot without the confinement of shoes.

Tannins, a Shoe’s Best Friend

It can therefore be concluded that leather tanned with vegetable tannins exhibits a selective action on bacterial flora, regulating the balance of the microbial ecosystem inside footwear. By now, you probably have a lot of questions:

The experiment compares synthetic materials and vegetable tanned leather. What about other tanning methods?

How can we be sure that the effectiveness against bacteria’s activity is unequivocally due to the  tannin and not other factors?

Assuming that tannin deserves the “credit”, what happens exactly? How does it counteract bacterial activity?

The Causes of Bad Odor

Have you ever asked yourself what exactly causes shoe odor? It is due to volatile fatty acids, gases released by bacteria as a result of the absorption of nutrients in sweat and dead skin cells. We have summarized the entire process in an infographic: understanding it in detail, will help you to prevent foot odor.