How many of you have been to a friend's house and kicked off your shoes only for them to ask you to put your shoes back on again? It's not because they don't shower — I mean, some people don't shower as often as they should.
Even so, people that don't shower often might not have stinky feet. Someone actually spent time to find out why.
But first, a little background
A team of entomologists headed by Renate Smallegange conducted a series of tests with sweaty feet and nylon stockings. (She also went around asking people to rub their sweaty feet on glass beads or capture their feet-stink in a plastic bag to get a whiff.) She wore her stockings for 20 hours straight and placed them where mosquitoes — some infected with malaria — were caged. The mosquitoes attempted to draw blood in the empty stocking (heh, suckers), and she found that mosquitoes with malaria were three times as more likely to be attracted by the scent of stinky feet.
In other words, your stink smells good to mosquitoes and they can't keep their lips off of you.
This led to a further study as to what it was about the stench of feet that attracted mosquitoes.
We know there's bacteria on our feet
Now, our feet-stink is comprised of different chemicals interacting with one another. It also has to do with live cultures of bacteria expelling waste and reproducing in between your damp sweaty toes. Our feet has, on average, 250,000 sweat glands per pair of feet. It also can produce about half-a-pints worth of sweat every day.
That leaves the bacteria with a lot of food to work with. The waste expelled is a combination of fatty acids that break down into the tragically familiar scent we're all wary of.
Scientists have attempted to pinpoint the bacteria responsible, but due to the sheer number living on our feet, it seemed virtually impossible...until James Reynolds at Loughborough University and his colleagues used their own feet to map out the bacterial colonies.
From their observations, six strains stood out to them: Corynebacteria, Micrococci, Propionibacteria, Betaproteobacteria, Brevibacteria and Staphylococci. The researchers were able to single these out because they all secreted a "potent chemical" named isovaleric acid. It is this acid that contributes to the stinky feet smell.
These bacteria were found most commonly on the balls of the feet — not by chance that this is usually the most pungent area. Some have compared the smell to Limburger cheese (the bacteria Brevibacteria is also responsible for its pungent smell).
Mosquitoes really love smelly feet
Smallegange found that depending on the combination of these stench-causing bacteria on your feet, it either increased or decreased your chances of getting bitten by mosquitoes. She found that feet with more Staphylococci were more susceptible to be bitten. And the malaria parasite, by making slight adjustments to the proteins in the mosquito's head, it was able to alter the sense of its smell and direct it towards the smell of rapidly decomposing fatty acids — our smelly feet.
Interestingly, researchers were able to bait mosquitoes using Limburger cheese — a cheese created with the help of Brevibacteria, one of the strains of bacteria that lives on your feet.
So thanks to malaria research, we're able to determine the actual reason as to why some people have unbearably stinky feet and some don't.