Why do socks stink?

What chemicals are responsible for the stench emanating from socks? If it's just sweat, why don't underwear or vests stink as much? Which gas am I inhaling when smelling socks to decide whether they need a wash?




According to the Wikipedia page, aptly named [Smelly Socks](https://en.wikipedia.org/wiki/Smelly_socks), it states that the smell



> 
> is a mixture of ammonia, fatty acids (in particular, [isovaleric acid](https://en.wikipedia.org/wiki/3-Methylbutanoic_acid)), and lactic acid.
> 
> 
> 


What makes sock odor unique is that socks often pick up small amounts of organic material when walking around without shoes on. When wearing shoes, they are in a warm semi-enclosed environment with a considerable amount of sweat infusing into them (it can be quite [warm and humid in shoes](http://www.aaqtic.org.ar/congresos/china2009/download/2-6/2-218.pdf)) particularly when exercising. A lot of the smell is due to bacterial action on the bits and pieces trapped in the socks themselves.


Interestingly, the Wikipedia article states that it is a topic of ongoing study, in part due to a possibility that the chemicals could be used in the battle against Malaria - [Using smelly socks to attract mosquitoes -- and combat malaria](http://www.zdnet.com/article/using-smelly-socks-to-attract-mosquitoes-and-combat-malaria/)


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In addition to the answer posted by @santiago, here is some information from the following article in the UK newspaper Daily Mail:


[The science behind stinky feet: Video reveals the processes that cause a nasty stench, and how to stop it](http://www.dailymail.co.uk/sciencetech/article-3160002/The-science-stinky-feet-Video-reveals-processes-cause-nasty-stench-stop-it.html)


The article has a video, produced by the American Chemical Society, that explains how the bacteria that live on your skin and in your shoes eat your sweat, producing an acid by-product that causes the smells.


A snippet from the article:



> 
> The three main bacterial waste products are propanoic acid,
>  methanethiol and isovaleric acid
> 
> 
> Methanethiol makes your feet smell like sulphur and cheese and is
>  produced from dead skin.
> 
> 
> Isovaleric acid also has a cheesy aroma, and a rancid vinegar-like
>  scent, while propanoic acid has a rancid sour smell.
> 
> 
> 


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