Why normal foot deodorant doesn't really eliminate foot odor — and what three studies say about the real solution

Foot odor is one of the most common hygiene problems—and at the same time, one of the least understood. Most people shower daily, wear fresh socks, and use foot deodorant. Yet the smell returns. Every single day. Without exception.

The reason for this has nothing to do with a lack of care. It has to do with bacteria.

To understand why probiotic skincare works in a fundamentally different way than classic foot care products, we developed a three-stage study design: an in-vitro study, a supplementary odor test study, and an in-vivo panel study. The results speak for themselves.

Foot odor is not caused by sweat — but by bacteria

Before we get to the study results, a basic understanding of the cause is important: sweat itself is odorless. The typical, unpleasant foot odor only develops when certain anaerobic bacteria on the skin break down sweat components and produce volatile, odor-active metabolic products in the process.

This means: anyone suffering from foot odor does not have a hygiene problem. They have a microbial imbalance problem. The skin microbiome—the natural bacterial community on the skin—has fallen out of balance. Odor-causing bacteria have gained the upper hand.

Classic foot deodorants and foot baths do not address this at all. They mask the odor with fragrances, reduce it briefly through antibacterial agents, or absorb moisture. The skin environment in which the odor-causing bacteria thrive remains unchanged. As soon as the effect wears off, bacterial activity resumes—the odor returns.

Study 1: In-vitro investigation — Can lactic acid bacteria displace odor-causing germs?

To investigate the biological basis of the probiotic approach, skin swabs from three subjects with noticeable foot odor were cultured on skin-like nutrient media and incubated at 37 °C in an in-vitro study.

The experimental setup included four groups: foot skin flora without additives, foot skin flora combined with lactic acid bacteria cultures, lactic acid bacteria cultures alone, and a sterile nutrient medium as a control. Ten different lactic acid bacterial strains were used, including Lactobacillus rhamnosus, Bifidobacterium lactis, Lactobacillus acidophilus, and others.

Result: In the petri dishes without lactic acid bacteria, dense, heterogeneous bacterial growth with a predominance of anaerobic, odor-causing germs was observed after four days. In the samples that were additionally treated with Lactobacillus cultures, the growth of these anaerobic bacteria was significantly inhibited. Instead, the lactic acid bacteria dominated the environment.

Microscopic images at 2500x magnification clearly confirm this finding. The mechanism of action is two-staged: lactic acid bacteria produce lactic acid, thereby slightly lowering the pH value on the skin. This slightly acidic environment is unfavorable for odor-causing bacteria. At the same time, the lactic acid bacteria spread on the nutrient medium and occupy the available resources—a displacement process known in microbiology as competitive inhibition.

Study 2: Supplementary odor test study — The sensory proof

Microbiological findings alone do not say whether the displacement effect is actually perceptible. Therefore, a supplementary odor test study was conducted: three volunteer subjects with no knowledge of the cultivation details evaluated the incubated bacterial cultures olfactorily on a scale from 0 (no odor) to 10 (unbearable).

The results are clear:

In all three cases, the addition of lactic acid bacteria cultures significantly reduced the perceived odor intensity. The combination of microbiological and sensory findings provides robust proof: lactic acid bacteria not only demonstrably inhibit the growth of odor-causing germs in the lab—the effect is also immediately perceptible to the human sense of smell.

Study 3: In-vivo panel study — What happens on human skin?

The decisive step is transferring the lab result to real-world application. In a prospective in-vivo observational study, the probiotic foot spray was tested on 21 subjects with noticeable foot odor.

Efficacy was evaluated in two ways: through self-assessment by the subjects on a scale from 0 to 10, and by independent odor evaluators who performed an olfactory check before application and after seven days.

Self-assessment results

Just 24 hours after a single application, 85.7 percent of the subjects recorded a perceptible change in foot odor. After seven days, 90.5 percent reported that the odor had further improved compared to day 1. The odor intensity fell on average from 5.33 to 1.05—a reduction of around 80 percent.

Results of independent third-party assessment

The results from the external evaluators are even more convincing. After seven days, they rated the feet of 20 out of 21 subjects as no longer smelling unpleasant. This corresponds to an efficacy rate of 95.2 percent according to independent third-party assessment.

Odor intensity in the third-party assessment fell on average from around 5.0 to below 1.5. Not a single subject recorded a deterioration.

Why the effect lasts for weeks to months

A common question: Why is a single application enough for such a long-lasting effect?

The answer lies in the mechanism. The spray populates the skin microflora with living lactic acid bacteria that settle on the skin and regulate the environment permanently. As long as the newly established microbial balance remains stable, odor-causing bacteria find no favorable conditions to multiply again.

How long this effect lasts is individually different and depends on environmental factors: wet or poorly ventilated shoes, socks with a high polyester content, or excessive sweating can once again stress the skin environment. Reducing such factors supports a stable microbiome—and extends the duration of the effect.

Three-stage proof of efficacy: A consistent overall picture

The three studies complement each other to form a cohesive picture of evidence:

In-vitro: Lactobacillus cultures demonstrably inhibit the growth of anaerobic, odor-causing bacteria from foot skin swabs.

Sensory: The inhibitory effect is not only microscopically measurable but also directly perceptible to untrained evaluators.

In-vivo: On human skin, the probiotic foot spray reduces foot odor to a minimum within seven days after a single application—with an independently confirmed efficacy rate of 95.2 percent.

Conclusion: Probiotic skincare as an alternative to classic foot deodorants

Normal foot deodorant masks. Disinfection kills in the short term—and damages the protective skin microbiome in the process. The probiotic approach targets the actual cause: the disturbed bacterial balance on the skin.

The present study results provide scientific proof that lactic acid bacteria can measurably and sustainably restore this balance. The probiotic foot spray is therefore not a cosmetic trick—but a biologically grounded intervention in the skin microbiome.

Heidis Best® — Probiotic foot spray with 10 lactic acid bacterial strains. Dermatologically tested. Efficacy confirmed by panel study and in-vitro investigation.