Foot odour: an objective look at the bacterial causes

What lies beneath

Anatomical fundamentals of foot skin explain why this specific area of the body is particularly susceptible to moisture. The sole of the foot possesses the highest density of eccrine sweat glands on the entire human body. Approximately 600 of these glands are located on a single square centimetre of skin. In contrast to the apocrine sweat glands in the axillae, eccrine glands produce a watery secretion consisting of 99 percent water. Furthermore, this fresh sweat contains dissolved salts such as sodium chloride, lactate, amino acids, and urea. In its original state, the sweat secreted by eccrine glands is completely odourless.

Odour only develops secondarily on the skin surface through the activity of the cutaneous microbiome. The humid, warm environment inside footwear provides an ideal breeding ground for specialized bacterial strains. Dominant species include Corynebacterium, Micrococcus sedentarius, Staphylococcus epidermidis, and Brevibacterium epidermidis. These microorganisms feed on the substances dissolved in sweat as well as shed corneal cells of the stratum corneum.

During this enzymatic degradation process, bacteria split proteins and lipids into short-chain carboxylic acids and volatile sulphur compounds. Isovaleric acid in particular, produced by the breakdown of the amino acid leucine, generates a sharp, cheesy odour. Butyric acid provides a rancid note, while volatile sulphur compounds such as methanethiol are responsible for faecal and cabbage-like nuances. The odour profile varies considerably depending on the composition of the individual skin flora.

Medically, a distinction must be made between increased sweat production, known as plantar hyperhidrosis, and odour-intense bromhidrosis. Hyperhidrosis can occur without any odour as long as the bacterial flora remains in balance. Bromhidrosis only develops when the moist maceration of the stratum corneum drastically increases the nutrient supply for odour-forming bacteria. In severe cases, pitted keratolysis (Keratolysis sulcata) is present, in which enzymatically active bacteria erode small, shallow craters into the stratum corneum.

Typical signs

The most noticeable symptom is a distinct, pungent, or sour odour that becomes perceptible shortly after removing footwear. The odour intensity usually increases after prolonged wear or physical exertion. However, in addition to olfaction, visible and tactile changes often appear on the skin, indicating a disrupted microbiome.

A typical sign is skin maceration. In this process, the stratum corneum swells due to continuous moisture. The skin appears whitish, spongy, and softened, particularly on the sole of the foot, the heel, and between the toes. This softened skin loses its natural protective function against mechanical stimuli and microorganisms.

With progressive bacterial colonization, punctate, crater-like defects often appear in the callus. These fine holes have a diameter of one to seven millimetres and occur frequently on the pressure-bearing zones of the forefoot and heel. This clinical condition of pitted keratolysis is often accompanied by a sticky skin sensation and reduced resilience of the sole of the foot.

This clinical picture must be differentiated from dermatomycosis, classic athlete's foot (tinea pedis). While bacterial bromhidrosis is primarily characterized by odour and maceration, athlete's foot is usually accompanied by redness, fine scaling, vesicle formation, and severe itching. However, bacterial imbalance and fungal infections frequently occur together, as the damaged skin barrier favours both types of pathogen.

Everyday causes

The development of foot odour is favoured by an interplay of external environmental factors, choice of clothing, and individual physical conditions. In modern everyday life, shoes and hosiery are central to this process, as they significantly determine the microclimate around the foot.

Occlusive footwear is among the main causes. Shoes made of synthetic materials such as polyurethane, synthetic leather, or rubber do not allow sufficient water vapour exchange. Moisture released by the foot remains inside the shoe. A warm, humid greenhouse climate develops, with a relative humidity of nearly 100 percent and temperatures around 35 degrees Celsius. Work and safety shoes of protection classes S2 or S3, as well as rubberised boots, are particularly susceptible to this problem due to their design.

The choice of hosiery is equally decisive. Socks with a high proportion of synthetic fibres such as polyester or polyamide can barely store moisture inside the fibre core. Although they wick away sweat, they hold it directly on the skin surface if the shoe cannot release the moisture. Natural fibres such as merino wool or specially processed cotton, on the other hand, exhibit significantly higher hygroscopicity.

Anatomical and biomechanical factors play an underestimated role. Malalignments such as splayfoot, fallen arches, or flatfoot alter pressure distribution during walking. In areas of increased pressure, the skin responds with increased callus formation (hyperkeratosis). At the same time, mechanical pressure and friction stimulate local sweat glands. Dense hyperkeratotic layers provide bacteria with abundant nourishment after moistening.

Additionally, systemic diseases and hormonal changes affect sweat secretion. Diabetes mellitus, hyperthyroidism, neurological dysfunctions of the autonomic nervous system, and hormonal shifts during puberty or menopause can massively increase sweat production. Psychological stress also leads to a sudden release from eccrine sweat glands via activation of the sympathetic nervous system.

When medical evaluation is necessary

In many cases, increased odour development can be corrected through adapted hygiene and material selection. However, there are clinical warning signs that require prompt medical diagnosis. This applies particularly to patients with pre-existing medical conditions.

If sweat production increases suddenly without high ambient temperatures or physical exertion explaining it, an evaluation should be performed. If sweat occurs asymmetrically on only one foot or is accompanied by night sweats, systemic causes may be present.

Dermatological or general medical consultation is also indicated if the skin exhibits deep cracks (rhagades), painful redness, or weeping wounds. If extensive bacterial infection of the subcutaneous tissue (erysipelas or phlegmon) is suspected, recognisable by warm, painful redness with swelling, rapid action is required.

People with known diabetic foot syndrome must have any skin change examined immediately by a specialist physician. Due to existing peripheral polyneuropathy, pain is often not perceived in time. A macerated skin barrier poses a high risk for bacteria to infect deeper tissue layers and cause severe complications.

What podiatric treatment can achieve

Professional podiatry addresses the mechanical and microbial causes of odour formation. The treatment process in the practice always begins with a thorough inspection of the foot skin, the interdigital spaces, and posture. The moisture state of the skin, the pH value, and any maceration are evaluated.

A central component is the professional removal of excessive calloused tissue as part of a podiatric treatment (podologische Komplexbehandlung, a comprehensive podiatric care procedure). The aim is to deprive bacteria of their breeding ground. Using rotating instruments such as diamond burs and ceramic cutters, hyperkeratosis is thinned out painlessly and precisely. Macerated skin areas in the interdigital spaces are also carefully cleaned and smoothed. A detailed overview of our treatment methods can be found in the /en/services section.

In addition to manual tissue management, restoring the skin's natural protective acid mantle plays a decisive role. Medical care foams containing active ingredients such as micro-silver, panthenol, or octenidine are used in the practice. Micro-silver possesses a broad-spectrum antimicrobial effect without burdening deeper skin layers or promoting resistance. It remains on the skin surface and inhibits the growth of Corynebacterium and Micrococcus.

In cases of accompanying skin problems or altered nail lamellae, the targeted use of physical therapies can be beneficial. In our practice, cryotherapy is used, among other methods, to modify tissue stimuli and support skin regeneration. The strictest standards for instrument reprocessing and disinfection according to RKI guidelines guarantee maximum safety. Detailed insights into our standards are provided in the /en/hygiene section.

A treatment session usually lasts between 30 and 45 minutes. Depending on the extent of maceration and new callus formation, treatment intervals of four to six weeks are recommended. Accompanying individual advice is provided on suitable relief options and orthotics to permanently reduce pressure-induced sweat stimulation.

What you can do yourself

Sustainable improvement requires the consistent implementation of structured care steps in daily routine at home. The key lies in combining proper skin care, targeted shoe management, and appropriate textile choices.

Daily hygiene should be aimed at preserving the cutaneous acid mantle. Clean your feet daily with lukewarm water and a pH skin-neutral syndet (pH value 5.5). Avoid strongly alkaline soaps, as they shift the skin's pH value into the basic range and thus promote the growth of Corynebacterium.

Thorough drying after washing is essential. Each interdigital space must be dried individually and carefully. Use a separate, soft towel for this purpose, which should be changed daily and washed at a minimum of 60 degrees Celsius. In the case of severely narrowed interdigital spaces, cool blow-drying on the lowest setting can be a gentle option.

Afterwards, apply a light, rapidly absorbing care product. Dry skin that is at risk of maceration benefits from foams containing 5 to 10 percent urea. Urea binds moisture in the stratum corneum without leaving an occlusive greasy film.

When selecting footwear and textiles, observe the following rules:

• Change your footwear daily and allow worn shoes to dry out at room temperature for at least 48 hours.
• Use shoe trees made of untreated stone pine or cedar wood, as they actively absorb moisture and release essential oils with a mild antimicrobial effect.
• Prefer hosiery made of merino wool or blended fabrics with silver threads, as these fibres effectively bind moisture and inhibit bacterial growth.
• Regularly disinfect the inside of shoes with a suitable shoe disinfectant based on alcohol or quaternary ammonium compounds.
• Consistently wash socks at a minimum of 60 degrees Celsius to reliably kill bacterial dormant forms.

Common mistakes

In podiatric practice, we regularly observe well-intentioned care measures that unintentionally worsen the problem. Lack of knowledge regarding microbiological relationships often leads to incorrect routines.

A widespread mistake is excessive scrubbing of the soles with harsh pumice stones or rasps. Strong mechanical irritation stimulates the epidermis to accelerate cell division. The skin responds with increased keratinisation. The resulting thick callus provides bacteria with even more degradation products after the next sweating episode.

Equally problematic is the use of highly concentrated home remedies such as undiluted vinegar baths or baking soda rinses. Strongly acidic or alkaline foot baths attack the skin's lipid barrier. The skin dries out, develops microscopic cracks, and loses its defensive capacity against pathogens.

The following errors occur particularly frequently in practice:

• Using antiperspirants on damaged or freshly macerated skin, which can lead to severe contact dermatitis.
• Wearing the same leather shoes on consecutive days without allowing the material the necessary drying time.
• Covering moist interdigital spaces with thick greasy ointments, which drastically accelerates maceration.
• Foregoing hosiery in closed footwear, allowing sweat to soak unhindered into the upper leather.

A concise case example from practice illustrates this. A 42-year-old warehouse logistics worker suffered from extreme foot odour and burning soles of his feet. To combat the odour, he washed his feet three times daily with antibacterial household soap and subsequently rubbed them all over with milking grease. He wore his safety shoes continuously five days a week. The result was massive maceration with onset of pitted keratolysis (Keratolysis sulcata). Only after switching to pH-neutral syndets, omitting the milking grease in favour of a micro-silver foam, and using a second pair of safety shoes in rotation did the symptoms completely subside within four weeks.

Scientific evidence and classification

Scientific research into cutaneous microbiology has provided essential insights into the aetiology of foot odour in recent years. Historically, odour was viewed primarily as a pure hygiene problem. Modern sequencing methods, however, show that the individual microbiome constitutes a complex biochemical factory.

A fundamental study by Marshall et al. [1] demonstrated that the colonisation density with Micrococcus sedentarius and Corynebacterium species directly correlates with the severity of pitted keratolysis and the extent of odour intensity. The authors showed that these bacteria produce protein-cleaving enzyme structures that dissolve the keratin structure of the stratum corneum.

In another clinical study, Stevens et al. [2] investigated the biochemical degradation pathways in eccrine sweat. They identified isovaleric acid as the primary lead odour compound. The results highlighted that it is not the mere presence of sweat, but the specific enzymatic activity of certain Corynebacterium strains that is responsible for the unpleasant odour.

Regarding material selection, textile research confirms clinical observations. A comparative study by McQueen et al. [3] examined the moisture and odour behaviour of different fibre types. It was found that animal protein fibres such as merino wool exhibit significantly lower retention of odour molecules compared to synthetic polyester fibres. Wool fibres bind moisture inside the fibre structure, depriving bacteria on the surface of free water.

The efficacy of topical silver preparations is also scientifically documented. The work of Lansdown [4] demonstrated the antimicrobial effectiveness of elemental silver in micronised form. The silver releases silver ions into the moist skin environment, which damage the cell walls of odour-causing pathogens and inactivate their enzymes without exerting cytotoxic effects on human keratinocytes.

Treatment in Memmingen

In our podiatric practice in the centre of Memmingen, we offer affected individuals a reliable and discreet point of contact for the treatment of skin and nail changes. FREITAG® Podologie GmbH combines sound medical expertise with modern treatment standards.

Owner Helga Maria Freitag has been a state-recognised podiatrist since July 2025 and qualified as a sector-specific practitioner in podiatry (sektorale Heilpraktikerin) since March 2026. As a specialist in cryotherapy and founder of Kältekammer Memmingen, she brings deep expertise to skin and tissue treatment.

Our practice at Kempterstr. 25 in 87700 Memmingen is easily accessible for patients from across the entire Unterallgäu region, the Allgäu, and Upper Swabia. If you suffer from persistent foot odour, skin maceration, or painful calluses, feel free to arrange an appointment for consultation and treatment. You can reach us by telephone on 089 15880714 or directly via our online booking option on the /en/contact page.