What causes stinky feet

The human feet with high levels of humidity and a rich supply of nutrients, provides an ideal environment for the colonization and growth of bacteria and subsequently is a site associated with the liberation of odor, also known as “stinky feet”. This microbial flora varies in number from <10 to >10⁷ micro-organisms per square cm ¹. One of the chief consequences of this high microbial load is the production of an unpleasant odor which has a distinct cheesy/acidic note ². Previous work has demonstrated that this odor emanates from the bacterial biotransformation of branched-chain amino acids, such as leucine and valine into volatile fatty acids, in particular isovaleric acid ³. The branched-chain amino acids are liberated via the degradation of the exfoliated layers of the stratum corneum under the influence of extra-cellular bacterial proteases ⁴. Alternatively, they originate as a soluble component of the secreted eccrine sweat ⁵. The key causative bacteria responsible for this biotransformation on the foot are Staphylococcus spp., but some species of Brevibacterium, Micrococcus and Kytococcus are biochemically competent at converting branched-chain amino acids to volatile fatty acids ².

Staphylococcus spp. isolated from the human foot have been shown to convert branched aliphatic amino acids, such as L-leucine, to short-chain methyl-branched volatile fatty acids, including isovaleric acid ². A study ⁶ of plantar skin patches of eight subjects, found isovaleric acid was detected in the plantar skin patches but was not detected in measurable quantities in any of the dorsal (top of foot) samples. The fact that isovaleric acid was not detected on any skin patches obtained from the dorsal surface but was present on the plantar surface is almost certainly attributable to the high numbers of Staphylococcus spp. residing at this site. Although staphylococci were present on the dorsal surface, it would appear that there were insufficient numbers to produce detectable levels of isovaleric acid. The levels of other volatile fatty acids that contribute to foot odor ⁷ were also significantly increased on the plantar skin patches compared to those obtained from the dorsal surface, indicating that staphylococci may play a major role in the generation of these acids also. The skin patch data support the notion that high numbers of bacteria, in particular Staphylococcus spp., are implicated in the production of foot odour. Variations in the spatial distribution of these microbes appear to be responsible for the localized production of odour across the foot, a notion put forward previously but until now not verified ².

These variations are a consequence of the different environmental, topographical and biochemical conditions encountered between different skin sites and are also a reflection of person-to-person variability ⁸. The plantar skin (sole of foot) displays a thickened stratum corneum ⁹, a reduced lipid content ¹⁰, contains one of the highest sweat gland densities found on the human body (620 ± 120 glands cm⁻²) ¹¹ and is subject to increased mechanical stress ⁹.

Previous culture and genomic-based studies have demonstrated that Staphylococcus is the most dominant organism present on the plantar surface of the foot, with Corynebacterium also providing a significant contribution ⁶. Micrococcus, Propionibacterium, Betaproteobacterium and Brevibacterium species also make up a significant contribution to the overall foot microflora in some subjects ¹². The spatial distribution of these bacterial populations across the foot has not been studied in any great detail. Eccrine sweat glands are the primary source of foot secretions and are present on both the plantar and dorsal surface, secreting a primarily aqueous solution containing inorganic electrolytes, free amino acids, lactic acid and urea ¹³. Unlike most areas of the body, the plantar surface of the feet have no sebaceous glands and also lack apocrine glands which are associated with odor production in the armpit.

One particular bacterium that has been linked with the generation of foot malodor is Kytococcus sedentarius ¹⁴. Strains of Kytococcus sedentarius isolated from normal feet are capable of efficiently degrading callus, which is mainly composed of keratin protein, into soluble peptides and free amino acids, which may then serve as direct substrates for malodor formation ⁴. The data obtained in the current study ⁶ suggest that K. sedentarius is not particularly prevalent on the plantar surface of the foot (20%) and that the generation of volatile fatty acids responsible for foot odor is not dependent on its presence. Whether or not this bacterium is associated with extremes of foot odor is open to question, what is clear though is that the generation of appreciable levels of odorous volatile fatty acids can be accomplished in its absence. The absence of large numbers of certain bacteria implicated in the production of foot odor such as K. sedentarius, Brevibacterium and Micrococcus is in agreement with previous studies that have investigated the foot microbiome ¹².

The intensity of foot malodor would appear to be associated with an increase in the total microbial load, along with elevated skin pH and minor pitting of the stratum corneum ¹⁴. Elevated hydration levels, as a consequence of the use of occlusive footwear and/or high environmental temperatures, lead to an increase in microbial numbers, particularly Staphylococcus spp. Under these conditions, the combination of increasing levels of eccrine sweat ⁵ and callus-degrading activity by the foot microbiota ⁴ leads to the liberation of high levels of peptides and amino acids which, in turn, serve as substrates for the production of stinky odor. Due to differences in the spatial distribution of the microbial population across the foot, the plantar surface is a major site of malodor production. Given the high microbial load and propensity of Staphylococcus spp. to colonize this site, it is also expected that that the inter-toe web space is an important site for malodor production on the foot.

How to get rid of stinky feet

So how can you stop your feet from stinking ? Well, you might not be able to stop stink completely because of the commonly present bacteria and your feet sweat glands. However, if you cut down on sweat, you’ll cut down on the foot odor.

Good foot hygiene is essential. Wash your feet daily with an antibacterial soap; be sure to wash between the toes. Dry the feet thoroughly, then apply cornstarch, foot powder or an antifungal powder to your feet. The presence of a fungal infection requires treatment. Topical creams may be tried initially (terbinafine, the azole group) but if extensive, a short course of an oral preparation may be required. The identification of the pathogen is useful in helping to decide between terbinafine and the cheaper preparation, griseofulvin.

Wear wicking socks made of natural or acrylic fiber blends that draw the moisture away from your feet instead of trapping it. Some synthetic blends are designed to wick moisture away from the skin and work best to keep the feet dry. One hundred percent cotton socks absorb moisture but do not wick it away from the skin and frequently lead to blisters, so they should be avoided.

It’s also a good idea to change socks during the day. Stash an extra pair of socks at school or at work, and change socks mid-way through the day. Wear shoes that are made of breathable materials.

A technique called iontophoresis, which uses water to conduct a mild electrical current through the skin, has been found helpful for people with sweaty feet. People can purchase iontophoresis machines for at-home use.

Home remedies for stinky feet

• Antiperspirants. Topical aluminium chloride hexahydrate 20% (available over-the-counter at chemists) should be trialled at night until sweat reduction is achieved. The frequency can then be decreased to several times per week. The effect is thought to be due to an occlusive action of aluminium containing particles in the upper epidermis and change in ionic transport within secretory cells ¹⁵. However, this is generally effective in only the mildest cases. Irritation can occur when the preparation is applied to other sites.

• Be clean. Wash your feet every day. Dipping your feet into a tub of water and scrubbing may be better than just letting the shower water splash on them. Be sure to dry your feet when you’re done.

• Wear the right socks. Cotton, some wools, and special knits made for athletes will absorb sweat and allow your feet to breathe. Put on a fresh pair every day, and also if the socks get damp.

• Make sure your shoes aren’t too tight. If they are, your feet might sweat more than normal.

• Switch shoes. Wearing the same shoes every day can make them smellier. Let them dry out for a couple of days before wearing them again.

• Kill those germs. You also might wash your feet with antibacterial soap. Setting shoes out in the sun also may help. An antibacterial wash in the shower, such as benzoyl peroxide 5% ¹⁶, is an important first step; but make sure this is washed away well as it has bleaching properties. Otherwise, topical antibiotics (may require a doctor’s prescription) such as clindamycin 1% or erythromycin 2%, or a combination product containing benzoyl peroxide 5% and clindamycin 1%, could be used (may require a doctor’s prescription). If unsuccessful, a course of oral antibiotics such as erythromycin for 7–10 days may be required.

• Wash shoes or insoles. Some insoles or shoes, especially sneakers, may be washable — a great way to kill odors and get clean-smelling shoes again. Be sure to dry them completely before wearing them.

• Avoid shoes made of plastic. Plastic and some human-made materials don’t let your feet breathe.
• Occlusive and rubber shoes often exacerbate the problem by increasing sweating.

• Go barefoot. Let your feet air out by letting them spend some time in the open air, especially at night. But don’t go barefoot too much — especially in the outdoors — because that can invite certain bacteria (like that Kyetococcus) to live on your feet!

• Don’t share shoes or towels with others. If you do, that may transfer stink-causing bacteria from other people’s feet to yours.

If you still have problems with foot odor, you can also try getting you odor-fighting powder or insoles. If nothing seems to work, you might want to see your doctor about what to do. The doctor may give you a special medicine to put on your feet.

For most people, foot odor can be controlled. The worst part about having stinky feet is that it’s embarrassing. If you’re worried about this, just keep your shoes on when you’re in social situations, like when you’re at school or riding in a car.

At home, keep your feet clean and go barefoot so they get some air. If your feet are clean and dry, those bacteria will have to find their lunch somewhere else!

Iontophoresis (the no-sweat machine)

If excessive sweating affects your hands, feet, or both areas, this may be an option. You will use this treatment at home. It requires you to immerse your hands or feet in a shallow pan of tap water. As you do this, this medical device sends a low-voltage current through the water. This can be done with tap water alone ¹⁷ or with anticholinergic drugs.

Iontophoresis using an anticholinergic solution, such as glycopyrrolate is superior to tap water ¹⁸. Some systemic absorption of the drug occurs, resulting in anticholinergic side effects for a day or so after treatment. This is generally limited to a dry throat, although it may also include blurred vision and dry eyes. The treatment is available only in specialized centers as the use of the drug in this manner is ‘off label’.

Many people obtain relief. Some people dislike that this treatment and it can be time-consuming.

Uses: Hands and feet

How it works: The electric current shuts down the treated sweat glands temporarily.

Most people need about 6 to 10 treatments to shut down the sweat glands. To get improvement, you begin by using the device as often your skin doctor recommends. At first, you may need 2 or 3 treatments per week. A treatment session usually takes 20 to 40 minutes.

Once you see results, you can repeat the treatment as needed to maintain results. This can range from once a week to once a month.

If this treatment is right for you, your skin doctor will teach you how to use the device and give you a prescription so that you can buy one. Some patients also receive a prescription for a medicine that they add to the tap water.

Contraindications: Pregnancy and a history of metallic implants such as orthopedic prostheses and cardiac pacemakers are contraindications to this treatment.

Side effects: Some people develop:

• Dry skin
• Irritated skin
• Discomfort during treatment

If you experience any side effects, tell your skin doctor. Making some changes often eliminates these side effects.

Prescription medicine

Some patients receive a prescription for a medicine that temporarily prevents them from sweating. These medicines work throughout the body.

Oral anticholinergics, such as propantheline, may be tried, but these usually require doses that cause intolerable side effects, including dry eyes, dry mouth and throat, and urinary retention, before they have any real benefit on the sweating ¹⁹, ¹⁷.

How it works: These medicines prevent the sweat glands from working. Athletes, people who work in a hot place, and anyone who lives in a warm climate should use extreme caution when using this treatment. The body may not be able to cool itself.

Uses: These medicines can effectively treat sweating that involves entire body. This medicine also can be an effective treatment for post-menopausal women who sweat excessively only from their head.

Side effects: The medicines that prevent the sweat glands from working can cause:

• Dry mouth
• Dry eyes
• Blurry vision
• Heart palpations (abnormal heartbeat)

The risk of side effects increases with higher doses. Before taking this medicine, you should talk with your skin doctor about your individual risks and benefits.

Botulinum toxin injection

Botulinum toxin for the management of palmoplantar hyperhidrosis is well reported ²⁰, ²¹, ²². The Botulinum toxin inhibits the release of acetylcholine from presynaptic nerve endings. When successful, this treatment has the advantage of long duration of symptom relief, often for at least 6 months in most patients ²², although a longer period of time has been reported ²¹. Botulinum toxin injections do not cure hyperhidrosis; your symptoms will go away gradually (usually in about a week) and return gradually. Follow-up injections are required to maintain dryness. Side effects include pain from the multiple injections required (the toxin diffuses approximately 1 cm from the point of injection and some form of analgesia is usually required, eg. methoxyflurane inhalation, nerve block, or in some cases, general anaesthesia), weakness of the intrinsic muscles of the hands ²¹, ²² and cost. When Botulinum toxin is used for plantar hyperhidrosis (excessive sweating of the feet), patients often report more pain during plantar injections and statistics indicate the treatment is less effective than when used for other body sites; indeed, some data suggests that 50% patients are dissatisfied with the results ²³.

Neutralising antibodies were once thought to limit the long term use of this treatment. However, Gordon et al ²⁴ report this is not a clinical issue for most patients undergoing long term treatment with botulinum toxin type A. Botulinum toxin contains the blood product human albumin and it’s use may be unacceptable to some patients. Botulinum toxin may interact with medications that affect neuromuscular transmission including aminoglycosides and curare like compounds, and this may last 3–6 months after administration ²⁵. A limited number of dermatologists offer this service, often in specialised clinics.

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