The science answer: Foot odor is caused by bacteria on our skin that eats the sweat and excretes waste that has a strong odor. It's perfectly normal to have bacteria on your skin, and it doesn't ordinarily produce a noticeable smell, but the sweat our feet excrete can't easily escape into the air -- it all collects on our skin and in our socks and shoes. The bacteria love this dark, damp feast and have a sort of feeding frenzy. Propionic acid (also called propanoic acid) is present in many foot sweat samples. This acid is a breakdown product of amino acids by Propionibacteria, which thrive in the ducts of adolescent and adult sebaceous (sweat) glands. As propionic acid is chemically structured similarly to acetic acid (vinegar), producing similar physical characteristics including odors, this may account for the foot odors identified as being vinegar-like smell by certain persons. Also: A foot odor that smells like ammonia may mean that you have a diet which is too high in proteins and/or you may be consistently dehydrated. If this is the case, an excessive amount of amino acids will be used for energy causing your sweat to smell like ammonia. Solution if this is the problem - drink more water and/or eat less protein. The solution? Wear loose shoes (such as sneakers) that allow your feet to breathe instead of constrictive shoes (such as boots) and wear cotton socks as they will trap the sweat. This will reduce the amount of sweat available for the bacteria to eat. If you own more than one pair of shoes, it is best to let each pair air out for 24 hours before wearing them again. It will also help if you wash your feet with antibacterial soap since this will kill much of the bacteria.