I have been observing the prevalence of stinky feet and shoes and realized a couple of things. First of all, stinky shoes are more common in humid environments. Secondly, they are usually shoes that have been sweated in, like running shoes. Dress shoes with which a person wears wool socks or no socks tend to be less stinky.
The reason is that bacteria thrive in moist environments like those created with sweat and cotton socks. With the right environment, the bacteria feast on the dead skin cells from your feet and produce stinky waste products.
It has recently been discovered that common foot odors are likely caused by Staphylococcus epidermis, a normal resident of the foot (Ara K, et al). One of the byproducts released by Staphylococcus epidermis as it degrades the leucine in sweat is isovaleric acid, or 3-methylbutanoic acid, and this is what causes the stink that is present in your sneakers and in locker rooms. Ironically, isovaleric acid releases volatile esters that are often used in perfumes. It is strange to think that stinky shoes and fine fragrances are so closely related. Although we can discern the difference between stinky isovaleric acid and its ester fumes, we all smell isovaleric acid to different degrees. According one recent set of genetic analyses, one person may be 10,000 times more sensitive to the sweaty stink of isovaleric acid than others (Menashe I, et al)!
More severe bacterial conditions of the foot are caused by Micrococcus sedentarius, or Kytococcus sedentarius, and sufferers of this infection are often left with severe skin damage and the stink from their feet is due to the production of thiols, sulfides, and thioesters, which contain sulfur (English JC, et al).
Preventing these bacteria from taking over your feet is as simple as keeping your feet clean and aired out. So, wash up those dogs and walk around barefoot a bit. Because isovaleric acid is not very water soluble, it is necessary to use some sort of soap to get the stink off your feet when washing them. Once your feet are clean a little bit of citral, citronella, or geraniol can inhibit the production of isovaleric acid (Ara K, et al). As far as remedying the sneakers, try putting them in the freezer for 24 hours (after placing them in a plastic bag, perhaps…). That should kill of some of the bacteria that have taken up residence.
English JC. Pitted Keratolyis. WebMD; August 30, 2006. Available at: http://www.emedicine.com/derm/TOPIC332.HTM. Accessed September 12, 2008.
Ara K, Hama M, Akiba S, et al. Foot odor due to microbial metabolism and its control. Can J Microbiol. 2006;52(4):357-364.
Menashe I, Abaffy T, Hasin Y, et al. (2007) Genetic Elucidation of Human Hyperosmia to Isovaleric Acid. PLoS Biology. 2007;5(11):e284.