Tannin, a selective antibacterial agent
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.
Each participant was given a new pair of shoes (ankle boot style) to be worn continuously for a period of 28 days.
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.
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.
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,
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
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 ideal antibacterial agent for shoes must act 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 antibacterial action, 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 antibacterial action is unequivocally due to the tannin and not other factors?
Assuming that tannin deserves the “credit”, what happens exactly? How does it impair 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.