Instituto Valenciano de Microbiología

Masía El Romeral
Ctra. de Bétera a San Antonio Km. 0.3
46117 Bétera (Valencia)
Phone. 96 169 17 02
Fax 96 169 16 37
CIF B-96337217


Odor feet (smelly feet): bacteria involved and control measures.

Information 02-02-2015.

The fundamental basis of foot odor is the sweat of the skin. Sweat itself is odorless. However, sweat together with other components from the skin, as are some fatty acids and elements from the desquamated cells are used as nutrients for microorganisms which are part of normal skin flora. By metabolizing these components from the skin, volatile organic compounds are released malodorous.

To understand the factors favoring the bad smell of feet in some pesonas, must be taken into account: 1) the amount of sweat that may accumulate in the foot, because in this sweat cutaneous fatty acids and sloughed cells are found, and They are creating a microenvironment in which bacteria thrive. In turn, the amount of accumulated sweat, varies from person to person, and the accumulated amount is determined by the type of tissue used socks and shoe type; 2) the bacteria in the skin, which vary in species and number of person to person. In this connection, some studies have found no significant relationship between the presence of a specific type of bacteria and foot odor, but the concentration (amount) of bacteria and foot odor. These bacteria produce enzymes (lipases and proteases) which facilitate the decomposition and metabolism of nutrients present in the foot sweat.

The foot odor is due, as we have said, the products (volatile metabolites) released by skin organisms, mainly bacteria, but sometimes some yeasts. These microorganisms to metabolize fatty acids and other components from the sloughed epithelial cells, vary in the type of odor, so that depending on which are the microorganisms, they release malodorous volatile metabolites, and the nature of the metabolites released varies the type of foot odor.

What are the microorganisms that form part of the normal skin flora of the feet?

Several studies of the skin flora feet and almost everyone agrees the following microorganisms, generally, with some variations from one study to another, in order of frequency and importance are:

Propionibacterium acnes (generally all individuals -100% - smelling feet).
Staphylococcus epidermidis (next in order of frequency, 86%), with other differentiated by sequencing (Staphylococcus hominis, etc.) species.
Brevibacterium spp.
Bacillus subtilis (11%).
Staphylococcus aureus (7%).
Micrococcus spp.
Corynebacterium spp.
Malassezia spp.

What are the characteristic odor of "smelly feet"?

Popularly have defined several typical odor reminiscent of from products used in food, and which also confers this typical smell to food and that are the consequence of the metabolism of microorganisms.

Some of these odors is reminiscent of some cheeses ( "Cheese-like"), attributed to the presence of Brevibacterium spp. or Staphylococcus epidermidis, which would release isovaleric acid (3-methyl-butanoic acid).

Another smells is reminiscent
of the "vinegar". This odor is due to the presence of propionic acid, acetic acid similar to vinegar odor. The appearance of this metabolite is due to the action of Propionibacterium spp. (mostly Propionibacterium acnes), present in the ducts of the sebaceous glands of the skin.

Smell "ammonia" (Ammonium-like).

Ammonia odor ( "sulfury") attributed to Brevibacterium spp. they would use the amino acid methionine sulfur to generate methanethiol which has odor "sulfur - containing" ..

What are the causes metabolites smelly foot odor?

The analysis by gas chromatography and mass spectrometry, of the fatty acids present sweat allowed contain the following components:

• Acetic acid.
• Propionic acid (similar to
the acetic acid smell).
• isobutyric acid.
• butyric acid.
• valeric acid.
• isovaleric acid (smell of cheese).
• caproic acid.
• caprylic acid.
• capric acid.

Of these fatty acids, the most significant would isovaleric acid, which can be generated from the amino acid L-leucine, bacteria that can be used as sole source of carbon and energy (Staphylococcus epidermidis, Staphylococcus aureus, Propionibacterium granulosum, Corynebacterium minutissinum and Bacillus subtilis).

How can you control foot odor?

As we mentioned, the main measure is to prevent sweat from building up, with other components because it can create the microenvironment conducive to the development of microorganisms.

This can be avoided by frequent washing of the feet, with the use of socks that facilitate transpiration, such as cotton socks because it facilitates transpiration tissue and also cotton, itself, has antibacterial properties. On the contrary, socks nylon or polyester, prevent perspiration, so some manufacturers pervade these socks with substances that try to neutralize the odor. Also, a frequent change of socks prevents too impregnated with sweat and odor is generated. Furthermore, shoes to facilitate transpiration should be used and allow ventilation of the footwear for drying the sweat accumulated. The accumulation of sweat inside the shoes can facilitate the development of microorganisms inside.

It has also been proposed the control of own skin microorganisms, applying thereon disinfectants tolerated by the skin, such as isopropyl alcohol solutions a few times a day, or sodium bicarbonate.

There are natural substances such as citronella and geraniol, besides having pleasant odor, are inhibitors of the generation of isolalérico acid, which as mentioned we bring the smell of cheese.

Some manufacturers of shoe insoles, the impregnated carbon made, facilitating drying sweat, even impregnated with silver salts having antibacterial, or sprinkled with boric acid for the same purpose.

An important aspect, when considering the use of disinfectants to kill bacteria that cause bad smell of the feet, is that they must be guaranteed to be used in the human skin contact repeated, ensuring that are risk of developing irritative processes or sensitizations, so they can be considered medical devices.

.Pruebas made in IVAMI:

• Cultivation of skin microorganisms and their identification.
• Evidence of inhibition of microorganisms on the skin, natural or chemicals.
• Safety tests for humans, by testing skin irritation or skin sensitization.

Recommended to learn the bacteria present on the skin of the feet skin shows:
• Swab impregnated into the clammy skin of the feet.

Preservation and shipment of sample:
• Refrigerated (less than 24 hours).

Cost of the test: