The human foot has on average around 200,000 sweat glands.  The majority of us wear shoes, sandals or some type of covered footwear throughout  the day.  These two factors working together is a major reason why we  have to deal with foot odor issues.  Typically men are more prone to  stinky feet than women. 
Interestingly enough a study found that while  females tend to sweat more often, men sweat more profoundly.  This  increased perspiration along with an enclosed area is an ideal  environment for stinky feet problems to arise.

As is the case with body odor and bad breath, foot odor is  most commonly a result of bacteria living on the surface of the skin.  They feed on organic materials in sweat and release waste compounds that have a pungent odor.  The most common of these odor compounds are two  types of acids; propionic and isovaleric.  The former is known to have a smell similar to vinegar while the latter tends to smell like moldy  cheese. 

Since most of us wear covered footwear throughout the day,  this creates two issues that relate to foot odor.  First, it causes heat.  With little to no ventilation, heat is not allowed to escape and  thus circulates causing our feet to perspire more.  Second, this excess  perspiration and elevated temperatures make for an ideal living space  for bacteria to thrive.  More bacteria means more stinky odor particles  being produced. 

The key to preventing or reducing stinky foot odor is to  target the source of the problem.  Foot powders, inserts and sprays help to control bacterial growth using antimicrobial agents such as parabens and/or
triclosan.  Wearing the right type of socks/shoes can also help  to cool your feet and reduce perspiration.  Some people even use  antiperspirant deodorants on their feet for this very reason. 

For more information about stinky feet and what you can do to reduce foot odor causes,
you can visit: http://bodymint.com/foot-odor-what-causes-stinky-feet/